PDDG Chapter 10 - Bridges

Chapter 10 of the MassDOT Project Development and Design Guide

10.1 Introduction

Based on the federal National Bridge Inspection Standards, a bridge is defined as a structure, including supports, erected over an obstruction, such as a transportation facility or a natural feature, that has a provision for carrying pedestrians, bicycles, and/or vehicles. Bridges come in a wide variety of configurations and structure types. This chapter provides a brief introduction to the topic of bridge planning and design including discussion of applications of bridges, contextual influences on bridge design, preliminary design guidelines, design of major bridge elements, and the inventory and management of bridges. 

For detailed information on the bridge design process, roles and responsibilities, please refer to the MassDOT LRFD Bridge Manual, Part I, which provides guidance on Load Resistance Factor Design and should be used along with Chapter 2 of this Project Development and Design Guide. 

Definitions 

A grade separation is the method of separating two transportation facilities, such as a road, railroad, pedestrian path or bikeway, by putting them on different grades so that traffic on one facility does not interfere with traffic on the other. Grade separations are accomplished by using either an overpass or an underpass. 

• Overpass: An overpass is a bridge that carries a road, railroad, pedestrian or bike facility over another transportation facility. 

• Underpass: An underpass is a road, railroad, pedestrian path or bikeway that passes under another transportation facility that remains on its original grade and is typically carried on a bridge. Underpasses are typically short and are not considered to be tunnels. 

A bridge consists of a superstructure and a substructure. 

• The superstructure includes the bridge deck, which carries the traffic, and beams, which support the deck. 

• The substructure supports the superstructure and includes the breastwalls and foundations of the abutments, the breastwalls and foundations of the wingwalls, and the cap, columns and foundations of the piers. 

Bridges can be constructed either entirely in place or be assembled out of prefabricated bridge elements at the site or by using a combination of these methods. 

A culvert is a structure which has no separate superstructure and substructure, but where the roof and sides (for three sided culverts) and the bottom (for four sided culverts) are constructed as a frame. Culverts are usually pre-cast in segments that are assembled at the site. The roadway (or other transportation facility) is usually constructed on fill placed over the culvert, but culverts can also carry traffic directly on their roofs. For inventory purposes, culverts are classified as bridges depending on their span length (see the “Inventory and Management of Bridges” section), however, despite this classification, culvert design standards, both hydraulic and structural, should be followed. 

The MassDOT Bridge Manual uses the following project definitions on a set of plans to describe the type of capital investment work being proposed: 

• Proposed bridge - New substructure and superstructure. Any existing bridge structure may be retained, in whole or in part, or may be removed in its entirety; however, no portion of the existing bridge structure will be incorporated into the proposed bridge structure. 

• Proposed superstructure replacement - All elements of the superstructure are replaced. Substructure elements are retrofitted to meet current code requirements and/or some, but not all, substructure elements are replaced. 

• Proposed bridge rehabilitation - Some superstructure and substructure elements are replaced and/or existing elements that are to remain are retrofitted to meet current code requirements. 

Other project descriptions may be used for bridge maintenance and preservation depending on the type of work being proposed, such as: PROPOSED DECK REPLACEMENT, PROPOSED BRIDGE REPAIRS, PROPOSED BRIDGE PRESERVATION, PROPOSED BRIDGE WIDENING, PROPOSED SCOUR REPAIRS.

The MassDOT Bridge Manual does not use the term reconstruction to mean a bridge replacement as reconstruction is an imprecise term that can also mean repair or rehabilitation to some people. Bridge Engineers use the more precise term replacement to mean just that, in alignment with the FHWA Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges.

10.2 Applications of Bridges

Bridges are used for a variety of applications as described in the following sections.  

Highway Grade Separations

Grade separations are often required when two or more roadways intersect at a location and when it is desirable to maintain free flowing traffic operations on at least one of those roadways. In these situations, bridges are used to physically separate the roadways. Most highway grade separations involve freeways or major arterials that intersect with other roadways. Bridges at these locations allow the highway below to safely accommodate high volumes of traffic without interference from the traffic above. Some controlling factors in the planning of a highway grade separation include highway geometry and available right-of-way. Highway grade separations are often combined with ramp systems to form interchanges described in Chapter 7. 

A bridge is designed to conform to the highway alignment and cross section. The bridge’s profile must be limited to grades that allow sufficient stopping sight distance, while at the same time providing the required under-clearance. The transition from the approach roadway to the bridge should be designed to present consistent visual cues to drivers so that their behavior is not altered. Other considerations that should be integrated into the design of highway structures include the following: 

• Generous lateral and vertical clearances to structural elements and other features should be provided. The MassDOT LRFD Bridge Manual, Part II, Chapter 2, has more guidance on establishing under-bridge geometry. 

• Substructure elements of the bridge, piers in particular, should be shielded from potential impact by errant vehicles. The MassDOT LRFD Bridge Manual, Part I, Chapter 3, has more guidance on protecting bridge substructures. 

• The design should support projections of activity levels by all users, consistent with state, regional and local plans and policies (see Chapter 3). 

• Aesthetically pleasing highway architecture should be considered. 

• Underpass structures should be as open as practical to allow light penetration, air circulation, and maximum visibility. In the case of long underpasses or tunnels, consideration must be given to the inclusion of rescue assistance areas, fire suppression, and ventilation. 

• Bridges over navigable rivers should be as open as possible to recreational (canoe/kayak) passage, and Coast Guard regulations apply for larger navigable waterways (see Chapter 2 of this PDDG for permitting guidance). 

• Highway grade separation structures should be designed with shoulders, curbing, lighting, and other highway elements that exist on the approaching roadway or that may be expected to be provided on the approaching roadway with future improvements.  

Bridges should also include pedestrian and bicycle facilities, if, in accordance with MassDOT policies and design guidance contained in other chapters of the PDDG.     

With respect to highway operations, there is no minimum spacing or limit to the number of grade-separated cross streets, however, considerable savings can be achieved by terminating some of the less important cross streets or combining nearby streets into single crossings. Engineering studies should be conducted to determine the effects of termination and the mitigation required to maintain continuity, safety, and access requirements for area roads. In some instances, frontage roads may be installed along the mainline to provide connectivity for users from terminated street to through cross streets. Factors that may affect the number and spacing of cross streets include: 

• Network connectivity and development characteristics. 

• Activity levels (pedestrian, bicycle and traffic volumes). 

• Location of schools, recreational areas, hospitals, and other public facilities. 

• Emergency service routes. 

The availability of adequate right of way may limit the possible structure types. Moreover, the construction process can also be adversely affected by the lack of right of way and can require staged construction. Additionally, considerations such as the bridge span length, soil characteristics, and skew may also affect the structure's design. 

In some instances, particularly in developed areas, the grades of local roads cannot be changed due to the surrounding context. In these situations, it may be necessary to depress the entire roadway into a boat section or tunnel, or alternately raise it, creating a viaduct. These facilities are much more expensive to construct and maintain than simple overpasses and underpasses and may require drainage pump stations, control of groundwater, underpinning of nearby structures, special lighting, and video systems for security monitoring. 

Railroad Grade Separations 

Grade separations are often required for safety and operational reasons when a roadway intersects a railroad. For most railroad grade separations, it is the roadway, pedestrian or bicycle facility that is carried over the railroad on an overpass structure, since these facilities can accommodate higher profile grades than railroads. However, if the grade separation is to be constructed in a location where there are many surrounding buildings, an underpass may be the most practical solution to avoid demolishing buildings to build up the approach roadway grades. However, railroad underpasses often present drainage problems, sometimes requiring the use of pump stations which can be costly and require ongoing maintenance. 

Some considerations when planning an overpass include the selection of the structure type, the horizontal and vertical clearance to the centerline of the track, the available right-of-way, drainage, train movements, and required coordination with the railroad company. Proper clearances are an important consideration in the early planning phase. To determine vertical clearance, it is important to determine the top of high rail elevation for approximately 500 ft. in each direction from the roadway and for a greater distance if a change in railroad grade is proposed.  

Crossings of a railroad right-of-way always require coordination with the railroad company, which may include negotiation of a formal agreement. In many cases, the structure must span the entire railroad right-of-way rather than just the active tracks. Train movements can also affect the construction process and, in the electrified AMTRAK territory, de-electrifying the overhead catenary can impose restrictions on the amount of time a contractor would have to work over the track area. Construction schedule and construction crew safety need to be addressed during the design phase.  

Crossings of Streams, Rivers, and Other Natural Features 

Bridges and culverts provide crossings over streams, rivers, and other natural features. Hydraulic analysis should take place early in project development to establish the hydraulic opening and to uncover unusual problems that become much more difficult to address at later stages, such as depth of scour. This is particularly important with respect to highway location. As discussed in Chapter 2, crossings of watercourses often require extensive permitting processes at the local, state, and federal level. When encountering streams, rivers, and other natural features the designer should reference the Massachusetts Stream Crossings Handbook (2018) and Chapter 14 of the PDDG. Where they exist, opportunities to replace hydraulically substandard crossings should be considered. 

There are two types of structures that are typically used in crossing watercourses: culverts and bridges. The MassDOT LRFD Bridge Manual, Part I, Chapter 2 provides guidelines on the applicable bridge structure types based on span length, as well as guidance on siting bridge substructures (abutments and piers) for watercourse crossings. 

• Culverts are designed to function with either with a submerged inlet (under pressure) or with free surface flow.  

• Bridges do not form inlet conditions or act as pressurized conduits since the flow line of a bridge is rarely fixed and the material along the flow line of a bridge is usually the same as the stream it crosses. 

Bridges and culverts are vulnerable to damage from floods, specifically flood-generated scour. To minimize the risk of damage, the hydraulic requirements of a stream crossing must be recognized and considered in all phases of project development, construction, and maintenance. Therefore, hydrologic and hydraulic analyses are required for all new bridges, bridge replacements, bridge widenings, and roadway profile modifications that may adversely affect the flood plain. While these analyses are discussed further in Chapter 8, the MassDOT LRFD Bridge Manual, Part I, Chapter 1, provides comprehensive information on conducting surveys required for detailed hydrology and hydraulic studies for bridges as well as methods for determining the predicted scour that needs to be taken into account during design. 

These analyses should also consider recreational water users by ensuring that they are not precluded from using the waterway due to limits on vertical clearance under the bridge. The designer should also consider routes for recreational access to the waterway during the design process. 

Both new and replacement bridges and culverts can also be used to improve the connectivity of habitat in certain locations, whether or not they are placed for a hydraulic function. The design of both bridges and culverts should consider the effects on wildlife habitat, fish passage, and other considerations described in Chapter 14. 

Pedestrian and Bicycle Facility Bridges 

Bridges can be constructed to carry pedestrian and bicycle traffic over an obstacle, usually a roadway, a railroad, or a watercourse. Given that extra travel distance is more acceptable for vehicular travel than for pedestrians and cyclists, it may be appropriate to include a separate bicycle and pedestrian crossing at locations where the existence of schools, places of worship, parks and open spaces, and other land uses generate large volumes of pedestrians or cyclists. Other factors affecting the decision to provide a pedestrian or bicycle bridge include: 

• A large number of children crossing

• Unacceptable traffic conflicts due to roadway width, high traffic speeds, and high traffic volumes

• Cost

Pedestrian routes on bridges have the same requirements for accessibility for people with disabilities as other sidewalks, as described in Chapter 5. Slopes can follow the roadway alignment, but cross-slopes cannot exceed 2 percent in the built condition (1.5 percent in design). Curb cut ramps are required at intersections. Where a bridge is not along the roadway right-of-way, its slope cannot exceed 8.33 percent in the built condition.

Pedestrian and bicycle underpasses beneath a roadway are typically discouraged due to the need to provide for drainage and lighting, unless the roadway surface is on a fill section of 15 feet or more and the pedestrian or bikeway can be graded level with the approach. 

10.3 Contextual Influences on Bridge Design

Bridges are highly visible elements of the transportation infrastructure in the surrounding landscape. Often, they traverse environmentally and ecologically sensitive sites, culturally or visually significant areas, or are visually prominent features in communities and other developed settings. Although bridges can have negative impacts on these environments, they can also be designed in such a way that they are pleasing or welcome additions to the landscape. The MassDOT LRFD Bridge Manual, Part I, Chapter 2, has more discussion on context sensitivity and aesthetics. 

Designing a suitable bridge requires that the designer pay careful attention to the details starting with an understanding of the setting in which the structure will be built and ending with the detailing of the bridge structure itself. Bridges can be designed to blend into the surrounding natural or built environment, if that is what is desired. Alternatively, bridges can serve as signature elements of the community by standing out from their surroundings. In either case, the designer must remember that the bridge can last many decades. The designer has the power to make the bridge a long-standing source of pride or of dissatisfaction. The role of the bridge in the built environment should be determined during the project development process with input from a broad range of interested individuals and groups. 

Understanding the Context 

The designer must understand the context of the site which the bridge will be built. If it is in a natural area, the designer should map the topography and natural features of the site. Usually, a bridge in a natural setting will be designed to fit into its setting rather than have the setting altered to fit a bridge structure. In urban areas, the designer needs to understand the community patterns in the vicinity of the bridge and the bridge characteristics suitable for the community setting. Specific issues with both natural and developed settings are described below.  

Environmental Resources 

Bridges often cross sensitive environmental resources such as wetlands, streams, and rivers. Although replacement of bridges is exempt from some permitting requirements, construction activities in these areas is usually regulated at the local, state, and federal level, as described in Chapter 2, and the permitting requirements for these projects can be extensive. MassDOT has established a footprint bridge program to replace bridges roughly within their existing location to help expedite replacement of existing deficient structures. 

The design of bridge projects needs to be based on an understanding of these resource areas and the potential short- and long-term impacts that the bridge may have on their hydrologic and ecological value. Design decisions such as crossing location, span length, substructure layout, and width can be adjusted to minimize impacts to these resources, regardless of the applicable regulatory requirements. Project design should also consider methods to provide erosion control and streambank restoration. 

Although bridges may impact these resources, they may also be included in a project design to reduce the impacts that causeways or other filling of the resource area could have. As described in Chapter 14, the inclusion of bridges and culverts in roadway projects can maintain habitat connectivity and reduce habitat loss especially for crossings of open watercourses.

Community Resources 

In a developed or urban setting, grade separations associated with bridges can result in either embankments or walls that create visual and functional barriers between different parts of the community. In some cases, the barrier effect of a grade separation can intensify the barrier effect of the roadway itself. On the other hand, longer grade separations, such as an elevated or depressed high-speed, high-volume roadway through a developed area can improve community connectivity if the crossings of the facility are well-designed and at appropriate locations.  

Pedestrian and bicycle facility grade separations can have similar effects as the grade separation of two roadways. For these facilities to be successful, they must be well-integrated into the surrounding pedestrian and bicycle network to prevent extra travel due to long ramp systems needed to achieve the grade separation. Additionally, these facilities are usually used to cross freeways, or other high-speed, high-volume roadways where pedestrians and bicycles are prohibited by regulation. In other situations, properly designed surface crossings of roadways generally provide the desired connectivity for pedestrians and bicycles. 

Grade separations of roadways or pathways and railroads is generally desirable. In many cases, railroads are developed along consistent grades and are often on embankments or below the surrounding grade. In these situations, grade separation is especially desirable to improve the safety and operating characteristics of both the roadway/pathway and the railroad. In locations where substantial modifications to the existing grades are required, the design considerations mentioned above are applicable. Similarly, paths built along railroad rights-of-way can often maintain grade separations at roadway crossings without adversely impacting the surrounding area. 

The considerations for grade separation of transportation facilities are also discussed in Chapters 6, 7, and 11. 

Bridge crossings of streams and watercourses can improve community connectivity and are less frequently associated with negative community impacts. However, in most cases, the aesthetics of the bridge crossings are very important due to their high visibility in the built environment, as discussed below. 

Aesthetics 

The visual quality of bridges can vary widely based on the type of structure, bridge profile and location, and the construction materials and details used. The aesthetics of a bridge start with the design of the structure itself. Those bridges that are considered to be the best examples of aesthetically-pleasing bridges are the ones whose primary structural systems represent the basic structural mechanics of how the structure carries the applied loads to the foundations. Therefore, a well-designed and aesthetically pleasing bridge is not one that is based on an abstract physical form, but, rather, one that expresses the natural, physical properties to which people intuitively relate. 

The expression of the structure alone is not sufficient to make a bridge aesthetically successful. For a bridge to be truly successful, it must be attractive on the following three levels at which the public experiences a bridge: 

• The overall bridge and how it relates to its setting

• The human-level experience of a pedestrian, or bicyclist, or boater traveling over, under or beside the bridge

• The driver-level experience of someone driving over or under the bridge

Each of these requires a level of detail to which a person can relate and with which a person can be visually engaged. Failure to adequately address the aesthetic expectations at any one of these levels will result in a bridge that people will find fault with, no matter how aesthetically successful the bridge may be on the other levels. 

Aesthetics on all levels are achieved by attention to detail and consideration of how each element of the bridge relates to the others. The design of the bridge must present a coherent overall vision of what each component part does and all architectural surfaces should be consistent with this vision. A bridge’s aesthetics are vastly improved when all of the component parts (piers, abutments, railings, and the superstructure) are designed to work together and complement each other visually.  

Therefore, the decisions that the designer makes regarding the structure type and substructure configuration will determine the aesthetics of the bridge more effectively than the application of superficial decoration after the basic bridge has been designed. MassDOT’s standard details contained in Part II of the Bridge Manual have been developed with this philosophy in mind. 

Historically Significant Bridges 

Older bridges have potential historical significance, either individually or as a contributing element to a historic district. This adds to their value as community assets, but also complicates the rehabilitation process if they are categorized as POOR or FAIR based on condition.  

State and federal statutes recognize the importance of preserving significant elements of our cultural and engineering heritage. Historically significant bridges are listed or eligible to be listed in the National Register of Historic Places. A bridge that is of a rare type, is unusual from an engineering perspective, or has historic significance because of location or association with an important event or person is a candidate for classification as a historically significant bridge (historic bridge). A bridge that is 50 years of age or older may also be a candidate for the list. 

As described in Chapter 2, historically significant bridges are addressed under the provisions of Section 4(f) of the Transportation Act of 1966 and may be demolished or moved only if it can be demonstrated that "there is no feasible and prudent alternative" to this taking of the historic property. Options that do not require the demolition of the bridge must be thoroughly considered including the no build option, as well as construction of a new structure at a new location or parallel to the existing facility. These alternatives need to be examined, evaluated, and thoroughly documented before any decision is made to demolish the bridge or to designate it for removal and transport to another location for non-vehicular reuse. Alternatives that keep the bridge in some level of vehicular service must also be examined; that is, rehabilitating the bridge in a way that does not destroy its historic integrity or retaining the historic bridge as part of a one-way pair or as an alternate scenic crossing. 

The Federal Highway Administration (FHWA) makes the final determination about whether the conditions of Section 4(f) have been met, and whether it has been demonstrated that there is no feasible and prudent alternative to the action that will remove and dispose of the historic bridge. Additional cost and additional displacements do not necessarily render an alternative imprudent or infeasible. 

Historic bridges that do not meet the criteria for vehicular use may be preserved for other uses. Preservation options include use for non-vehicular transportation purposes at the existing or relocation site, or use as a historical exhibit or monument at the existing or a relocation site. Preservation for bicycle/pedestrian use or as a historic monument at the existing site may be a viable option if the replacement structure's horizontal alignment can be adjusted to bypass the historic bridge.  

10.4 Highway Design Considerations

Before determining the appropriate structure type for the site, the preliminary roadway geometry, including vertical and horizontal alignment and cross section, must be determined. While the bridge is designed to accommodate the roadway cross section and horizontal and vertical alignment, nevertheless the highway and bridge designers need to work together to arrive at a roadway design that provides for the necessary clearances and freeboard, and allows for reasonable span lengths. 

Horizontal and Vertical Alignment

It is preferable that bridge structures should be on a tangent alignment, as long as the overall geometric design of the highway is not sacrificed. A tangent alignment affords easier geometric design of the bridge and easier bridge construction, thereby resulting in a lower structure cost. In areas where it is not feasible to build structures on a tangent alignment, curved structures are possible. Where curved structures are built, their geometry should fit the curve geometry for the roadway sections. Tightly curved alignments can significantly restrict the type of superstructure. Basic design criteria for horizontal alignment can be found in Chapter 4 of the PDDG.  

The vertical curvature of structures should generally conform to curvatures on sections of roadway for the same conditions of traffic and terrain described in Chapter 4 of the PDDG. For bridge decks that would otherwise be flat, either a small crest vertical curve or a slight profile grade over the bridge is recommended throughout the bridge length to improve bridge deck drainage. Basic design criteria for vertical alignment can be found in Chapter 4 of the PDDG. 

Cross-Section 

For any grade separation structure, a constant roadway cross-section with a clear roadway should be provided over the structure to provide a seamless connection for all users of the transportation facility. For example, where motorists take practically no notice of a structure which they are crossing, driver behavior is the same or nearly the same as at other points on the highway, and sudden, erratic changes in speed and direction are unlikely. However, a different cross section on the structure from that on the approaching roadways may be appropriate where future changes in the roadway cross section are desirable. As noted earlier in the section on Highway Grade Separation, the structure should provide desirable bicycle and pedestrian accommodation in accordance with MassDOT policies and design guidance contained in other chapters of the PDDG.

The multimodal accommodation and cross-section features found along the adjacent roadway segments should also be included on the bridge cross-section. It is not usually necessary for the bridge deck to be substantially wider than the approaching roadway, but the design of the bridge structure should include consideration of possible future widening. Generally, the width of the travel way and shoulder lanes should be consistent with the existing or planned future cross section of the adjacent roadway. In terms of additional width:  

• A 2-foot setback from the shoulder or bike lane to bridge rails or parapet walls is required.  

• Approximately 1 to 2 feet of additional sidewalk width is desirable to account for shy distance from the railing or parapet wall when sidewalks are provided. 

For bridge replacement and rehabilitation projects (such as footprint bridges), the designer should provide multimodal accommodation as close as possible to that found along adjacent roadway segments. During rehabilitation and especially for bridge replacements, it is often possible to modify the structure to provide, or to allow for the easy addition of, pedestrian and bicycle accommodation on the bridge. Additionally, for a rehabilitation project, if multimodal accommodation is available along a corridor, except for the bridge, the designer should evaluate whether retrofitting the existing bridge to provide accommodation is possible in lieu of replacing the structure. 

Stage Construction and Traffic Management 

While it is usually preferable to close the bridge for construction, in many situations this is not possible and some accommodation of vehicular, pedestrian and bike traffic may need to be made during the construction period. Some factors to consider are pedestrian and bicycle activity through the bridge site, ADT, location of emergency facilities such as fire and hospitals, length of detour, and the width and character of the streets on the potential detour route, to see if they can or cannot accommodate the detour traffic. 

The first accommodation would be to consider building the bridge in phases, also called "stage construction." First, is the width of the existing bridge such that can accommodate a single reversible lane of traffic. This would be possible if the ADT is low enough to permit this type of staggered operation without creating large backups. If the bridge is wider, perhaps it can accommodate two narrow lanes for bi-directional traffic. Either of these traffic management schemes need to be reviewed with the bridge designer, to determine if the bridge structure lends itself to be cut in the way needed to accommodate the number and width of lanes. In some cases, if the replacement structure will be wider to accommodate all modes of traffic, there is the possibility to offset the bridge alignments to provide the number of lanes needed for the first stage and the new bridge will be built wide enough to carry the number of lanes needed for the second stage. 

If stage construction is not possible and if there is enough space available, consideration can be given to building a temporary bridge that will take all of the traffic off the existing bridge alignment to allow the construction of the replacement bridge. 

Pedestrian and bicycle traffic should also be considered in the stage construction schemes. The designer should determine if there will be enough room to allow a pedestrian path to be maintained through the construction site or not and if bicyclists can safely share the road during the construction stages. 

For limited access highways where there is a wide median, consideration should be given to building a new permanent bridge in the median area, which will be used by one of the barrels that will be permanently relocated to this alignment. Once the bridge is built, the other barrel, that will remain in its present alignment in the final scheme, will be shifted to this bridge and its bridge will be replaced. Once that bridge is built, then both barrels will be shifted to their final alignment and the existing bridge on the abandoned alignment will be demolished. 

If there is no acceptable traffic management scheme to build a bridge on a conventional schedule, consideration should be given to using accelerated bridge techniques with prefabricated bridge members to rapidly replace the bridge in a matter of days. The community could be agreeable to this if they are guaranteed a short period of inconvenience rather than having to deal with the inconvenience of stage construction over more than one construction season. 

10.5 Preliminary Bridge Design

The MassDOT LRFD Bridge Manual, Part I, Chapter 2, provides detailed guidelines for conducting the preliminary bridge design phase. It is during this phase that all major investigations that are required for the design of the bridge are performed and the configuration of the recommended bridge structure is arrived at, considering: 

• Span lengths 

• Structure material type  

• Vertical clearance  

• Hydraulics (freeboard)  

• Foundation type 

• Accommodation of utilities 

• Speed of construction  

• Aesthetics 

• Cost 

The results of these investigations from the Preliminary Bridge Design phase, as outlined in MassDOT LRFD Bridge Manual, Part I, Chapter 2, are contained in these four report deliverables: 

• Hydraulic Report (for bridges over water) 

• Geotechnical Report 

• Preliminary Structures Report (if considering re-using portions of the existing bridge) 

• Bridge Type Selection Worksheet 

The final deliverables of the Preliminary Design Phase are the Sketch Plans, which are a conceptual presentation of the proposed structure or proposed rehabilitation. It allows the Designer and MassDOT to agree on the principal components of the structure type or the rehabilitation scheme to be pursued in the final design phase, since the Sketch Plans show all major features to be incorporated into the Construction Drawings.  

Hydraulic Report 

The Hydraulic Report is produced in two phases, preliminary (which informs alternative selection) and final (which is only performed for the preferred alternative and contains more detail). For the preparation of the Bridge Type Selection Worksheet, a Preliminary Hydraulic Form is prepared that gives the basic design flood elevations and design and check scour depths for the different structure types and bridge openings being evaluated. Once the proposed type of structure is arrived at and the bridge opening dimensions are finalized, then the final Hydraulic Report will be prepared which will be used for the final bridge design. The MassDOT LRFD Bridge Manual, Part I, Chapter 1, provides comprehensive information on conducting surveys required for detailed hydrology and hydraulic studies as well as methods for determining the depth of scour that must be taken into account during design, while MassDOT LRFD Bridge Manual, Part I, Chapter 2, provides guidelines on the preparation and presentation of both the preliminary and final Hydraulic Report. 

Geotechnical Report 

The Geotechnical Report is a required document used to present the anticipated subsurface site conditions and make any design and construction recommendations for the foundation and earthwork aspects of a bridge project. It is prepared in accordance with the guidelines set forth in MassDOT LRFD Bridge Manual, Part I, Chapter 2. The Geotechnical Report is based on the subsurface exploration program that is described in MassDOT LRFD Bridge Manual, Part I, Chapter 1, and is conducted early in the preliminary design phase. A well thought out, planned and executed program is crucial in obtaining an accurate representation of the underlying subsurface conditions. This program should consider any historical records and complement this information with borings, probes, test pits, geophysical methods, and field and laboratory testing to characterize the project site. Borings are typically the primary method of exploration and allow collection of soil samples and rock cores for visual descriptions and testing. If rock is encountered, a minimum 10-foot rock core is required to ensure that bedrock was encountered and not just a boulder. Other methods for investigating and testing the subsurface conditions, soil characteristics and substructure geometry should also be considered to supplement conventional borings. These include:  

• Probes to determine the hidden geometry of the substructures

• Cone penetration tests for thick deposits of alluvial soils

• Vane shear tests for cohesive soils

• Geophysical testing

Geophysical testing is encouraged to supplement a more conventional program of borings. Geophysical testing can be done prior to scheduling borings or after to fill in the data gaps between discrete boring locations. There are a variety of methods that can be used to identify foundation geometry, unsuitable layers, obstructions and to determine soil and bedrock profiles over a project site. 

Preliminary Structures Report 

If there is the potential for rehabilitating the existing structure or if certain elements are being considered for re-use, such as substructure elements as part of a superstructure replacement, a Preliminary Structures Report is required. This report presents the results of a full field evaluation of the elements to be retained, the results of materials sampling and evaluation, and the results of preliminary structural analysis of those elements to determine if they can carry the new loads. Material sampling of the concrete is especially important, since concrete can be subject to freeze-thaw deterioration, Alkali-Silica reactivity, and chloride contamination that can contribute to reinforcing bar corrosion. Complete guidelines for conducting these investigations and the material sampling and testing required are provided in MassDOT LRFD Bridge Manual, Part I, Chapter 2. The results of the Preliminary Structures Report are used to make a final decision on either the rehabilitation or re-use option for the design phase. 

Bridge Type Selection Worksheet 

The purpose of the Bridge Type Selection Worksheet (BTSW) is to streamline the type selection by guiding the Designer through a step-by-step process to identify the existing site features and project parameters and constraints that affect the bridge and which must be addressed, and then narrow down the range of possible bridge structure types to only those that best address them. The MassDOT LRFD Bridge Manual, Part I, Chapter 2, has the outline for the BTSW and guides the Designer through the process of identifying, first, the site features, then the project parameters. Next, the Designer identifies the feasible structure types that would address the site conditions and project parameters. Afterwards, the Designer is guided through the process for locating substructure units, establishing span lengths, and determining the impacts on clearances and freeboard. Finally, once the spans are set, the Designer selects the most appropriate superstructure material type for the site.

10.6 Bridge Design Considerations

The final structural design of a bridge proceeds in accordance with the AASHTO LRFD Bridge Design Specifications and the MassDOT LRFD Bridge Manual, Part I, Chapter 3. The Bridge Manual provides Massachusetts-specific design guidelines where AASHTO is silent or where the AASHTO provisions fall into a grey area that requires clarification in order to have consistency of design. The Chapters that make up the MassDOT LRFD Bridge Manual, Part II and the MassDOT LRFD Bridge Manual, Part III provide standard details of typical bridge elements, such as substructures, beam types, deck details, and bridge railings and barriers, to be used in preparing the construction plans. Part II Chapters contain conventional construction details while Part III Chapters contain guidelines for converting the Part II details into pre-cast or prefabricated details for accelerated construction. 

Curbs and Railings 

Since a bridge is a structure that carries an elevated transportation facility over another feature, a bridge railing or barrier must perform a dual function, that of safely restraining a user of the bridge, such as an errant vehicle, from running off the bridge, while at the same time protecting the feature underneath from any collateral damage from an incident on the bridge. Since bridge railings or barriers are typically located at the edge of the bridge deck immediately adjacent to the drop off, bridge railings and barriers are physically connected to the bridge structure and are designed to have virtually no deflection when struck, unlike typical longitudinal roadside barriers. Bridge barriers are normally constructed as a solid concrete shape, bridge railings as a metal or concrete post-and-rail system, or a hybrid of a metal railing mounted on a solid concrete shape.  

A bridge railing or barrier protecting vehicular traffic must meet performance characteristics: 

• The railing or barrier must not allow the impacting vehicle to penetrate the railing

• The railing or barrier must smoothly re-direct the impacting vehicle

• The height of the railing or barrier must be such so that the impacting vehicle will remain stable and will not roll over the railing

These three characteristics can best be evaluated from a full-scale crash test. The current standards for crash testing bridge rails and barriers are found in the AASHTO Manual for Assessing Safety Hardware (MASH). A computer-generated crash test simulation can provide insight into the bridge rails performance as well; however, it is only a simulation and may not replicate some of the more complex real-world vehicle-railing interactions that could affect the railing’s actual performance. 

The bridge railing or barrier is only one part of the overall roadside safety system, which must function effectively as a unit. Bridge and highway designers cannot terminate their respective design responsibility at the end of the bridge. Both disciplines must collaborate to ensure a safe and effective transition between the bridge rail or barrier and the approach roadway guardrail system. The most fundamental effort is to make sure that one system transitions smoothly to the next without potential snag points and that the two are functionally compatible. A bridge railing or barrier terminated or transitioned in an improper manner may result in an unacceptable hazard. 

Where a bridge also serves pedestrians, there are generally two options for accommodating them. For lower speed roadways, one option is to provide a sidewalk with a raised curb to separate the pedestrians from the roadway and to place a single bridge railing at the back of sidewalk that performs the function of both a traffic railing and a pedestrian railing. The curb height should be the same as what was crash tested. 

The second option is to completely separate the pedestrian walk from vehicular traffic by a traffic barrier. For this option, a pedestrian railing specifically designed for that purpose is needed at the outer edge of the bridge structure to protect pedestrians from the drop off. A traffic barrier between the roadway and sidewalk is recommended when the design speed equals or exceeds 50 mph. If the design speed equals or exceeds 40 mph but is less than 50 mph, an appropriate traffic barrier may be considered where bridge-specific conditions will allow it without interference to pedestrian movements, traffic flow, or other features. In all cases, this side of the road traffic barrier still has to be terminated in a manner that does not present a blunt end hazard or a tapered launching ramp to errant vehicles. A curb side traffic barrier can likewise pose a hazard to trucks turning into or from an adjacent intersecting street. 

An aesthetic bridge railing may have to be considered for a highly visible bridge in a scenic or culturally important area or in response to public input. However, the ability of the bridge railing to safely contain and redirect the errant vehicle should never be compromised for aesthetics. Treatments that have no impact on the bridge railing’s crash-tested traffic face can be applied to a concrete barrier. In other cases, coatings of different colors applied to a standard metal bridge railing are enough to enhance its appeal.  

Where appropriate, open railings should be used to provide views of water bodies or the surrounding landscape. In locations where a see-through decorative or historic railing is desired, another consideration would be to use a crash tested traffic railing in front of the decorative railings as long as it did not detract from the intended appearance of the decorative railing. If this solution is selected, the traffic railing still needs to be terminated or transitioned in an acceptable, safe manner to prevent an unacceptable hazard. 

All railings and handrails must follow the accessibility requirements of 521 CMR.

Utility Considerations 

Utilities, whether carried on the bridge, overhead, or sometimes under the bridge structure, must be identified during the Preliminary Design Phase and accommodated during the final design phase. In some cases, a subsurface utility exploration program must be undertaken to identify the type and exact location of buried utilities. Other than water and sewer mains, which are typically owned by municipalities and are installed by the bridge contractor, most all other utilities are owned by the various utility providers and must be removed or installed by then. For this reason, early utility coordination is vital. 

Accommodating utilities may also cause problems in design. If a bridge needs to be as shallow as possible for profile and clearance reasons, it may not have the depth to accommodate a large size utility. There may also be many utilities located on a bridge so that it is difficult to relocate them several times during stage construction. In these situations, consideration should be given to providing a separate utility bridge that is separate from the highway bridge and which is built first so that all utilities can be relocated onto it before the main highway bridge construction begins. 

Designers also need to coordinate the construction schedule with the utility companies to allow for smooth construction operations. These activities may include:  

• Coordinating and identifying periods of time when the utility can be deactivated during construction 

• Moving overhead wires temporarily to allow cranes to erect beams

• Obtaining utility design requirements, such as radii for bending the utility, type of support to be provided (e.g., rollers)

• Protection of buried utilities during construction operations

10.7 Inventory and Management of Bridges

MassDOT places highway bridges into two categories based on span length.  

1. The first is the federal definition of a highway bridge, found in the federal National Bridge Inspection Standards (NBIS), which defines a bridge as having a span greater than 20 feet.  

2. The second is the Massachusetts definition of a highway bridge, found in Massachusetts General Laws (MGL), Chapter 85 Section 35, which defines a bridge as having a span 10 feet or greater.  

For both categories of bridges, the span length is measured along the centerline of the roadway. MassDOT maintains an inventory of bridges of both categories and it includes not only MassDOT owned bridges but also municipally owned and those owned by other state agencies, such as the MBTA. MassDOT also maintains an inventory of pedestrian, bikeway, and utility bridges. MassDOT conducts inspections of all MassDOT and municipal-owned bridges, compiles this information with inspection information from other state agencies, and sends this combined inventory to the FHWA.

Assessing Bridge Conditions – Inspection 

All work that MassDOT performs on bridges starts with an assessment and understanding of the bridge’s physical condition. This is done through a comprehensive bridge inspection program. Under the federal NBIS regulations, MassDOT is responsible for ensuring that federal definition bridges are inspected according to the NBIS guidelines. MassDOT also inspects the MGL definition bridges in accordance with the same NBIS guidelines. As a service to the Commonwealth’s cities and towns, MassDOT inspects municipally owned bridges of both categories in addition to those that it owns. 

The results of these inspections are then used by MassDOT engineers to determine the need for work, whether it be immediate, as is the case with critical structural and safety findings, maintenance contract work, a site specific preservation project, or programming the bridge on the STIP for replacement or major rehabilitation. 

MassDOT Bridge Inspection Program 

MassDOT’s goal is to fully meet the federal National Bridge Inspection Standards regulations (23 CFR Part 650 Subpart C). To meet these regulations, MassDOT has issued policies and procedures for its MassDOT’s Bridge Inspection Program which are found in the MassDOT Bridge Inspection Handbook 2015 Edition. MassDOT performs the following main types of bridge inspections: 

• Initial Inventory Inspection – Initial inspection for a new bridge or rehabilitated bridge 

• Routine Inspection – Federally required full inspection every two years 

• Special Member Inspection – Those members that make a bridge Structurally Deficient are inspected more frequently, every year or every six months 

• Fracture Critical – For steel bridges, inspecting non-redundant steel tension members that if they fail could result in the failure of part or all of the bridge 

• Underwater Dive Inspections – Underwater inspection requiring scuba divers to access piers, abutments and their foundation below water level

Please refer to the Bridge Inspection Handbook for other types of inspections and their frequency that MassDOT performs. 

Reporting the Results of a Bridge Inspection 

After completing a bridge inspection, the bridge inspectors prepare a comprehensive inspection report that contains text describing their findings, sketches with dimensions showing the deteriorated areas, and photos documenting the deterioration and those other findings.   

The inspection report also includes the condition ratings that the inspectors assign to the three main elements of a bridge: the deck, the superstructure (beams supporting the deck), and substructure (the abutments and piers). The condition rating is a number from 0 to 9, where 0 indicates a failed element while a 9 indicates a pristine element.  The inspectors also assess the category of any deficiency found and the urgency of repair. These findings are described in the “Category of Deficiency and Urgency of Repair Section” below. 

Finally, the inspectors report on the condition of the bridge based on the bridge’s National Bridge Elements (NBE). National Bridge Elements, formerly known as core elements, are the nationally recognized elements that make up a bridge, such as linear feet of abutments and wingwalls, linear feet of beams, area of deck, etc. The inspectors determine the quantity of each NBE that falls into one of four condition states. Condition states are defined by the level of deterioration, with a condition state of 1 indicating good condition and a condition state of 4 indicating a very deteriorated condition. For a bridge in perfect condition, 100% of the quantity of an NBE would be reported in condition state 1. As the bridge deteriorates, this quantity would start to be divided among the other condition states. 

MassDOT uses an internally developed Bridge Inspection Management System that employs the 4D database platform to store the inventory data in addition to the bridge inspection reports, the condition ratings, and the NBEs and their condition states.  The 4D Bridge Inspection Management System is also used to generate reports, analyze bridge statistics, and to support the bridge inspection business process. 

Category of Deficiency and Urgency of Repair 

MassDOT has four categories of deficiencies and three urgencies of repairs as described in the Bridge Inspection Handbook.  The deficiency categories are: 

• Critical Structural – A deficiency in a structural element of the bridge that poses an extreme unsafe condition. 

• Critical Hazard – A deficiency in an element of the bridge that poses an extreme hazard or unsafe condition to the public but does not impair the bridge’s structural integrity. 

• Severe/Major – Deficiencies that are more extensive in nature and require more planning and effort to repair. 

• Minor – Deficiencies that are minor in nature, do not impact the structural integrity of the bridge, and can easily be repaired.

The urgency of repair categories are: 

• Immediate – Inspectors are to immediately contact the District Bridge Inspection Engineer and receive further instructions from him/her. 

• ASAP – Action/Repair should be initiated by the responsible party upon receipt of the inspection report. 

• Prioritize – Repairs shall be prioritized by the responsible party and performed when resources are available. 

Critical Structural and Critical Hazard deficiencies are considered critical inspection findings and require Immediate urgency of repair to address the deficiency and keep the public safe. These may include restricting traffic from the deteriorated area or providing a temporary repair while a more permanent one is designed and implemented. In extreme situations, this may also include closing the bridge to all traffic. There is also a reporting form and documentation procedure for critical findings that is outlined in the Bridge Inspection Handbook that documents the chain of contact between the Bridge Inspection Unit and the party responsible for the maintenance of the bridge and the action and date taken by the responsible party.

Severe/Major deficiencies typically have an ASAP urgency of repair and are typically addressed by MassDOT’s Emergency Repair Contractors, in the case of MassDOT bridges, or by town forces or their on-call contractors in the case of a town owned bridge. For some of these more complex repairs, the contractor has a pay item for engineering services that allows the contractor to hire an engineer to design the full, permanent repair.

Minor deficiencies typically require a Prioritize urgency of repair and are incorporated into a structures maintenance contract or a bridge preservation project. 

Assessing Bridge Conditions – Bridge Rating 

For the safety of bridge users, in addition to the bridge’s physical condition, it is equally important to determine the maximum weight of a vehicle with cargo that the bridge may safely carry. Federal National Bridge Inspection Standards regulations require that all federal definition bridges be load rated and, if they rate below legal truck weight limits, they need to be posted for load. Massachusetts General Laws also require this to be done for Massachusetts definition bridges as well. The MassDOT LRFD Bridge Manual, Part I, Chapter 7, provides more guidance on the load rating and reporting of the rating results. 

Bridges are load rated by determining the capacity of bridge members based on the strengths of the materials that make up the member. Next, this capacity is reduced by the demand on capacity from the bridge’s dead loads (e.g., beam weight, deck, pavement, etc.), leaving behind how much of the bridge member’s capacity is left to carry vehicles. The weight of vehicle is calculated by dividing this net member capacity by the load effect from the vehicle being rated. If the ratio is greater than one, then the bridge has sufficient capacity to carry that vehicle. If the ratio is less than one, then the bridge does not have sufficient capacity. The maximum weight of vehicle is determined by multiplying the legal weight of the truck being rated by this ratio and this is the weight that is displayed on the posting sign. 

Massachusetts rates all MassDOT and municipal-owned roadway bridges to determine the safe load by truck type including: a 2-axle truck, a 3-axle truck, and a 5-axle tractor trailer truck. When needed, MassDOT will post signage indicating that a bridge can handle less than the statutory load. MassDOT will also rate bridges for two additional classes of vehicles: Specialized Hauling Vehicles (SUV) and Emergency Vehicles (EV), in alignment with Federal legislation. 

The procedure for load rating bridge members that have undergone some level of deterioration is similar, except that the measured deterioration is subtracted from a bridge member’s section properties and these revised section properties are used to calculate the bridge member’s capacity in its deteriorated state. Sometimes, even though the bridge has undergone some deterioration, it still rates above the statutory load for all three truck types that are typically posted. In other instances, the deterioration is extensive, and the bridge requires posting for load. 

If the deterioration is limited to a few members, then those members may be isolated with barriers to prevent traffic from going over them, thereby allowing the bridge to remain open without load posting. In other cases, the District may decide to perform structural repairs to address this deterioration so that the bridge may remain un-posted and fully opened to traffic. 

Not all bridges that require posting do so because of structural deterioration. Older bridges may not have been designed to current truck standards. In these cases, the bridge may still require posting even though it may be in Fair to Good condition. 

MassDOT’s Bridge Programs 

MassDOT has two major capital programs for improving bridges and addressing deficiencies identified through inspections and ratings: 

• Preservation program 

• Replacement and rehabilitation program 

Bridges are selected for each program based on their condition category and the risk-based priority ranking described below. 

Bridge Condition Categories 

Outside of the emergency repair contracts that MassDOT uses to address deficiencies with immediate and ASAP urgencies of repair, MassDOT uses the bridge condition information to determine candidates for bridge preservation program and the bridge replacement and rehabilitation program.   

Based on the bridge inspection condition ratings, bridges are sorted into the following three categories according to the federal condition definitions: 

• Good (condition rating 7 and greater) 

• Fair (condition rating 5 and 6) 

• Poor (condition rating 4 or less) 

Bridges categorized as Poor (formerly known as Structurally Deficient) are considered to be at the end of their useful life and in need of replacement or major rehabilitation. Bridges categorized as Fair are considered to be potential candidates for preservation, which will address their deficiencies and extend their useful life. Bridges categorized as Good are in like-new condition and require only routine maintenance. 

Bridge Prioritization System 

MassDOT has developed a risk-based system for ranking bridges that uses the bridge inspection condition rating and NBE data to rank all 5,000+ federal definition bridges in the Commonwealth. One of the key features of this system is the use of the AASHTOWare Bridge Management software to predict the change in the Health Index of a bridge over 15 years. This percent change in the Health Index is a measure of the rate of deterioration of a bridge. In addition to this measure, the Prioritization System also considers the current condition loss of the bridge and several highway factors including detour length, ADT, functional classification of the roadway, geometric deficiencies of the roadway on the bridge, and the bridge’s load rating. All three are combined to arrive at a rank value that is then used to sort all of Massachusetts’ bridges to arrive at their rank. Currently, this system is used only for federal definition bridges. 

Bridge Preservation Program 

The MassDOT Bridge Preservation Program can be either funded with federal aid or non-federal aid. The preservation program is divided into two main parts: contracts that support work in multiple locations and site-specific contracts, which support varying levels of preservation from individual component repairs to full bridge preservation efforts. 

Various locations contracts are funded through non-federal aid exclusively and are intended to allow the District Bridge Sections to quickly respond to inspection findings or load rating results through work orders. Work orders are assigned at District discretion and candidate selection is exclusively determined by the District Bridge Engineer or their designees.   

For the site-specific contracts the selection of candidates is a collaboration between the District Bridge Sections and the Headquarters Bridge Preservation Unit since the condition of the bridges is ever evolving and influenced by the various locations contracts. Inspection data is used as the baseline for evaluation of candidates with an emphasis on fair condition elements or on bridges which may have a poor condition element but which do not rise high enough in the rank for selection as part of the replacement program. While considering a candidate bridge’s rank, selecting a preservation candidate bridge also considers other factors including: 

• Current expenditures through various locations contracts which indicate a potentially greater need than can be accomplished without site specific project. 

• Extent of the bridges deficiencies and condition to see if they fit the scope of work for preservation. 

• The degree of deficiency and its anticipated impacts over the short- and long-term including whether the deficiency creates accelerated deterioration of the structure. 

• Geographical location to determine if it can be grouped with other bridges as part of a corridor project to maximize a contractor’s mobilization.

• Upcoming adjacent or overlapping projects such as roadway resurfacing projects that would include non-bridge scope.   

This latter type of preservation work is intended to address bridge deficiencies before the roadway is resurfaced so that once the new pavement is put down, it does not have to be torn up again for bridge work. If this isn’t completed in advance consideration is given during these projects to include specific bridge work required to ensure longevity of the new wearing surface. 

Identification of candidates is also constrained by the allocated funding. As candidates are identified a preliminary estimate is developed to determine if the candidate project will fit within the proposed funding allocations. If the year is filled the bridge is noted for reevaluation in a future year. As design is developed, more information may become available which would indicate more deterioration has occurred and that this bridge is no longer a good candidate for preservation, and a major rehabilitation or replacement project is warranted instead.

Bridge Scoping for Site Specific Preservation Projects 

Scoping for site specific preservation projects begins with a site visit of bridge staff and the designer to determine the current needs of the structure. Since the condition of the structures needing preservation typically change with each freeze thaw cycle and winter salt application season it is crucial to visit the structure and not rely on inspection data, which is collected on a two-year cycle for bridges that are not significantly deteriorated. The data collected during this site visit will inform the scoping meeting which will ultimately determine which intervention strategies will be utilized or evaluated if multiple potential alternatives have been identified.   

Generally, preservation actions are divided and categorized as follows; bridge washing, bridge drainage system, joints, wearing surface, deck, superstructure, substructure, and traffic safety. Preservation activities can range from in-kind patching and repairs to railing upgrades or full replacement overlays. The scoping session is generally utilized to provide guidance for the designer as to which areas to pursue and if there is a need for additional studies to determine issues such as material testing, identification of water infiltration, or causes of unique conditions found. 

Scoping is heavily reliant on the condition of the bridge specifically, the changes in deficiencies from project initiation. For this reason, preservation projects are generally bundled to allow for flexibility in adding or subtracting structures based on the current deficiencies and pricing. Projects are scoped no greater than a year before they are expected to be advertised with a requirement to perform a quantity level verification just before the final submission of plans, special provisions, and estimate to ensure that the scope adequately covers the intent of the project but also fits within the programmed funding. 

Scoping sessions are held virtually with representatives from each discipline that may impact a project. The scoping session begins with the identification of the project location and a big picture summary provided by the Designer which helps attendees determine if their attendance is required. Since each preservation project has very different needs for environmental, traffic, safety, highway, pavement, and right of way there are typically attendees who can identify they will have no needs within the project scoping. Once an overview is completed the scoping checklist is reviewed live to ensure comments are accurately incorporated. The scoping checklist includes a separate bridge preservation tab to assist in the identification of the bridge preservation actions expected as part of the project based on the site visit and the project purpose. Many times, preservation projects are focused on a specific issue such as concrete patching or painting which are typically different contractors. 

After the scoping session the designer will finalize the checklist and all parties invited to the scoping meeting are provided an opportunity to review and comment on the checklist. These comments are addressed by the designer and then the scoping checklist is approved at which time the designer will prepare their design fee either to 25% if alternatives analysis is required or through the end of the project if the preservation actions are well established and no alternatives need evaluation. 

The bridge preservation scoping sessions are a new addition since the program has grown. These sessions are key to the success of the program as the projects need to be well defined for accelerated design schedules to be met. Accelerating design schedules reduces the project development durations therefore preventing additional deterioration and inherent quantity increases as the extents of deficiencies grow. 

Bridge Replacement and Rehabilitation Program 

The MassDOT Bridge Replacement and Rehabilitation Program is federally funded, so candidate bridges must be identified and put on the STIP. This program addresses bridges that are in Poor condition and relies on the Prioritization Program to help in the selection of candidate bridges. 

The list of ranked bridges is sorted by District and then sub-sorted to create two groups of bridges within each District list: those that meet the definition of Poor and those that don’t. The Poor bridges are then sorted again by the funding categories they are eligible for: NHS, non-NHS-On-system, and Off-system. The MassDOT Office of Planning provides spending targets for each funding category. In selecting candidate bridges, Poor bridges are considered based on their rank with input from Districts based on the bridge’s local importance for the local and regional economy, emergency services, delivery services, etc. A preliminary cost estimate of the project is prepared and the costs are added up so that they do not exceed that year’s target. If the sum of costs exceeds the target, some bridges are identified as candidate bridges for subsequent years. 

Once the STIP is fully programmed, the STIP is considered finished and is ready for approval by the MPOs and FHWA.  

Bridge Scoping for STIP Projects 

While bridge inspection data is used to determine the rank of a bridge and, since bridges on the STIP are generally in Poor condition, more than likely they will require some level of replacement, the actual decision of an intervention strategy to pursue is arrived at in the scoping session. The bridge inspection reports provide insight into the bridge elements affected by the deterioration and the pervasiveness of this deterioration throughout the structure thereby helping to identify the strategy to be pursued in the project development stage. 

In some cases, all elements of a bridge: deck, superstructure, and substructure, are affected, and the decision to pursue a full replacement is readily evident. However, it may be that only the superstructure has been markedly affected by deterioration while the substructures may appear to be in satisfactory condition, in which case a superstructure replacement may be all that is needed, and material sampling and structural investigation is needed to confirm that the substructure units can be re-used with confidence. 

Thus, a scoping session is held to give the designer guidance on the course of action to pursue including all that they will need to consider and address in their work. The purpose of this scoping session is to identify all preliminary engineering work and investigations that will be required to bring the project up to the 25% design stage. All relevant disciplines are invited to this scoping session, including Project Management, Bridge, Highway, Geotech, District Projects and Bridge, Complete Streets, Environmental, Right of Way, Utilities, and representatives from the municipality in which the bridge is located. If the bridge is over a stream or other body of water, representatives from the Hydraulics Unit are also invited. 

In the past, the scoping session was held on-site with all representatives from all parties present in person. Now, these scoping sessions are held using virtual meeting applications. This has proven to be very effective, as it is easier to assemble all the disciplines virtually than in person at the site. 

To prepare for the session, the Designer performs a site visit to document the site, identify any constraining features, such as houses, utilities both overhead and buried, any drainage structures, natural features such as topography and the roadway alignment and grade, and the condition of the bridge. 

The first part of the scoping session begins with the Designer’s presentation of the field visit. Next, all parties go over the standard project scoping checklist, where each discipline has a section where they can present their requirements for the project. Going over the checklist also allows the disciplines to discuss and negotiate when there are conflicting requirements that cannot all be reasonably accommodated. Local input from town representatives also helps identify local needs and future plans for development or utilities as well as needs for traffic management and accommodation during construction. Finally, the checklist identifies the environmental and other permitting documents that the designer will need to prepare and what the design deliverables through the end of the 25% design stage, including the level of review, public participation, and public hearing requirements. 

At the conclusion of the scoping session, the checklist is finalized and all parties that were present are given the opportunity to review the checklist and provide comments. Once comments are received and addressed and the scoping checklist is approved, the designer uses it to prepare their design fee through the completion of the 25% design stage. 

After the scoping phase, design follows the LFRD bridge design manual for pre-25% through final design.

10.8 For Further Information

• MassDOT LFRD Bridge Manual, 2013 

• MassDOT Bridge Inspection Handbook, 2015  

• Massachusetts Stream Crossings Handbook, Massachusetts Division of Ecological Restoration, 2018.