NCHRP Research Report 880: Design Guide for Low-Speed Multimodal Roadways (1) provides best practice guidance to the designer by referencing a range ofacceptable elements, criteria and values for critical dimensions for design of low- to intermediate-speed(45 mph and lower design speed) roadways with a mix of users and (2) assists designers in establishing a balance between operational efficiency, comfort, safety, and convenience for modes on the low- and intermediate-speed roadways. The report also includes detailed design case studies of design processes. The material in this report will be of immediate interest to design practitioners and stakeholders involved in the planning and design of streets and roadways that serve a mix of motorized and non-motorized users on facilities designed for low and intermediate speeds.
There is increasing recognition that successful roadway geometric design must provide an appropriate balance of service and safety for all users, including the consideration of cyclist and pedestrian users, and be coordinated with the uses and “context” of adjacent properties. The 2011 AASHTO A Policy on the Geometric Design of Highways and Streets (Green Book) recognizes this need, but provides limited specific guidance on how to incorporate this balance in the roadway design process. Little established practical engineering design guidance exists on how to effectively integrate and balance the service to all transportation modes along the same facility, corridor, or intersection. Most available geometric design guidance is based upon design for a single mode and does not fully address or incorporate the often competing needs of other modes requiring attention.
For example, because of the vulnerability of pedestrians and cyclists, they are involved in a disproportionate number of serious injury and fatal collisions at intersections. Factors that include a roadway functional classification, roadway operating speed, current and projected user demand, adjacent context, and community goals, present a challenge in creating geometric designs that adequately recognize and provide for a mix of transportation modes and trip types, and reflect the priority that each should be given. This can be particularly difficult for certain intermediate-speed situations, which present a combination of multimodal features that may not integrate well or be congruent with each other. The design process should apply to roadways of all types, but particularly those in an environment of limited right-of-way, congested traffic conditions, and other routine multimodal design challenges. In addition, there was a need for a methodology for optimizing the balance of tradeoffs between geometric design elements and safety and operational performance for all users of these facilities.
Under NCHRP Project 15-48, Gresham, Smith and Partners was asked to develop a set of integrated guidelines that will help designers accommodate all users in the design of low- and intermediate-speed roadways, including:
- Methods to identify the mix of users that need to be served on various roadway functional classifications (context, area types, etc.) and speed categories (low and intermediate speeds);
- Methodologies supported by empirically based research and best practices that can balance and optimize how geometric design elements provide for safe and effective operation;
- Geometric design parameters for the types and designs of facilities to serve all users, and;
- Examples showing how facilities representing various roadway functional classifications and speed categories have been or could be designed effectively.
In addition to the guidelines published as NCHRP Report 880, the research agency’s final report that documents the entire research effort is available at: