State departments of transportation (DOTs) are committed to modally integrated and well-functioning transportation systems and providing safe, accessible, and reliable systems for all users, including those who walk, bike, or use mobility assisted devices. However, for local and state DOTs that operate these systems, constrained financial and human resources have made it rather difficult to maintain their current assets in good repair, let alone build new infrastructure. These constraints often result in the prioritization of motorized vehicle projects over those advancing the use of active transportation modes. Active transportation facilities also often lose out because of the unavailability of adequate information and decision-making tools needed to assess the potential safety performance tradeoffs when evaluating alternatives, including walking and biking facilities.
To support all modes and improve the transportation system’s safety and equity, it is critical to determine the potential use of the system by those who bike, walk, or use mobility assistive devices (devices such as motorized scooters and bikes). However, counts of people walking and biking are often unavailable or collected in a manner that is unusable for crash prediction or for comparing the needs of all users to support location-based (e.g., segments and intersections) equitable decisions. Exposure models for active transportation can potentially help circumvent this problem to allow DOTs to consider all modes of transportation in their project planning and development process in a fair and equitable manner.
Exposure models enable state DOTs to incorporate predictive information into their decision-making process when volume data for those who walk or bike is not available or when the DOTs do not have funds to collect data at every potential project location. Even when volume data is collected for some specific project locations, DOTs may not be able to sustain that collection on a consistent, regular basis due to financial constraints. This non-inclusion has a particularly negative impact on lower-income areas where significant gaps for active transportation modes already exist. Exposure models have the potential to address this deficiency. The multivariate nature of this approach would allow for the necessary planning, design, and operational considerations upfront in different combinations and contexts. The information provided by the models regarding potential safety performance can be used in the decision-making process during project planning and development for active transportation modes.
Research is needed on how the use of exposure models can help advance a decision-making framework that considers how best to achieve an integrated multimodal approach on public roadway system. It will also help supplement other ongoing predictive modeling and systemic tools developments for active transportation. Furthermore, the results of this research could also be used by others to develop additional safety performance functions (SPF) that could supplement models being developed under the NCHRP Project 17-84, Pedestrian and Bicycle Safety Performance Functions for the Highway Safety Manual, with additional functional classes and contexts.
The objectives of this research are to:
1. Advance the predictive safety performance methodologies for pedestrians, bicyclists, and those using mobility-assistive devices (such as motorized scooters and bikes) using exposure estimates and prediction models. Develop models and predictive methods for use by state and local DOTs of all sizes to determine potential exposure to help evaluate the likely safety performance at a given location.
2. Develop guidance and resources to support the implementation of the developed methodologies that can be used to inform multimodal decision-making in different design and land use contexts and also for different modal priorities.
The research plan shall be executed in two phases and, at a minimum, comprise the following tasks.
Task 1. Plan and hold a virtual kick off meeting to review the Amplified Research Plan with the NCHRP project panel. NCHRP approval of the Amplified Research Plan is required before future tasks can commence.
Task 2. Conduct a critical review of the road safety literature to identify pedestrian and bicyclist exposure factors associated with road safety. Factors to consider will include socioeconomics, demographics, land use, multimodal accessibility, and roadway characteristics, among others. Equity-related mobility also needs to be considered. The review should summarize factors considered, discuss related modeling efforts, and identify gaps in the current state of knowledge and practice on the research topic.
Task 3. Identify data currently used as well as public data that could help develop exposure and safety prediction models for use in identifying appropriate multimodal roadway locations. Develop a comprehensive data collection, management, and validation plan. The plan should include metadata for raw and processed data, data ownership information, data restrictions (if applicable), and recommendations for data archiving. This preliminary plan will be presented to the NCHRP for approval.
Task 4. Prepare a detailed Phase II work plan that describes a methodological framework for developing exposure and safety prediction models (this may include conventional as well as new analytics). Examine key factors for evaluating the safety performance of urban and suburban facilities, using characteristics such as land use, demographics, speed, traffic volumes, roadway width, lanes/shoulders/medians, sidewalks, bicycle lanes/tracks, multimodal network connectivity, access management, etc. These factors should help determine current and future system usage by active transportation modes, if compatible land use or walkable and bike-able facilities were to be provided. In addition, using proven exposure prediction methods for active transportation modes, various design treatments for active transportation users in different contexts should be evaluated to examine how they affect the likelihood of crashes. A plan for model validation should also be provided.
Task 5. Prepare an interim report documenting the literature review analysis, datasets, and proposed Phase II work plan.
Task 6. Develop methods for exposure and safety prediction, as proposed in Phase I and approved by the NCHRP. These methods should be capable of evaluating existing and future conditions and be practical and readily implementable by state and local DOTs of all sizes to help evaluate potential safety performance at a given location. Discuss in detail the impact of the significant variables, including magnitude and sign of impact (+/-), with the purpose of improving the scientific understanding of active transportation exposure and safety performance.
Task 7. Prepare a user-friendly guide that facilitates the implementation of research outcomes and illustrates, with at least one case study, how the developed models can be used to inform multimodal decision-making in different design contexts and also for different modal priorities. The guide should include a discussion of how changes in the road environment may impact safety outcomes for all users and how mitigation strategies can be applied to address those changes that impact safety. A user-friendly, updatable, and easy to maintain spreadsheet tool that can be used and maintained by state DOTs should also be provided with the guide.
Task 8. Prepare a final report documenting the research development process (including assumptions), research results, conclusions, and recommendations. Guidelines on incorporating exposure factors in safety research should also be provided. The final set of deliverables shall include research datasets with a data dictionary and the program (and source) code used for the development of statistical models to support future research and check replicability/reproducibility of research results.
Task 9. Conduct at least one virtual workshop and one webinar/presentation for a relevant audience, such as the AASHTO Committee on Safety or the AASHTO Committee on Non-Motorized Transportation. The NCHRP must approve the material content and target audiences for these activities. Prepare a draft article suitable for publication in the TR News, highlighting the research findings and recommendations and their implementation strategies. However, no commitment to publish a TR News article is implied. Information regarding TR News publication can be found on the TRB webpage via the link below:
Deliverables shall include the following, at a minimum. Proposers may suggest additional deliverables to support the project objectives.
1. Technical memo presenting results of Tasks 2 and 3 and a plan for collecting, analyzing and managing data.
2. Virtual presentation to the NCHRP project panel on the findings of Tasks 2 and 3.
3. An interim report documenting the results of Phase I and Phase II work plan.
1. A final report that documents results, summarizes findings, draws conclusions, presents an implementation strategy or plan for the research results, and makes recommendations for additional research.
2. A user-friendly, updatable, and easy to maintain spreadsheet tool and guide that facilitates the implementation of research outcomes and illustrates how the developed models can be used to inform multimodal decision-making in different design contexts and for different modal priorities. The guide should also include a discussion of how changes in the road environment may impact safety outcomes for all users and how mitigation strategies can be applied to address those changes.
3. At least one virtual workshop and one webinar/presentation for a relevant audience, such as the AASHTO Committee on Safety or the AASHTO Committee on Non-Motorized Transportation. The NCHRP must approve the material content and the target audience for these activities.
4. A draft article suitable for publication in the TR News, highlighting the research findings and recommendations and their implementation strategies. Information regarding TR News publication can be found on the TRB webpage
STATUS: Work has been initiated. The interim report is expected December 2023.