The National Academies

NCHRP 15-48 [Active]

Guidelines for Designing Low- and Intermediate-Speed Roadways that Serve All Users

  Project Data
Funds: $500,000
Staff Responsibility: Waseem Dekelbab
Research Agency: Gresham, Smith and Partners
Principal Investigator: Marshall Elizer, Jr., P.E., PTOE
Effective Date: 7/22/2013
Comments: Research in progress

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 to consider and serve all users, but provides limited specific guidance on how designers evaluate their needs and address them during the roadway design process. The need for a more “complete” roadway design process has been well recognized in the design profession for many years and much research has been published on the importance of designing for safe and efficient travel of all user modes along a facility. However, 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, pedestrians and cyclists are involved in a disproportionate number of serious injury and fatal collisions at intersections, because of their vulnerability. Factors, including 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. Thus, there is a need to develop design guidelines that address the full range of users of low- and intermediate-speed roadways. 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 design challenges. There is a need for design guidance that is both integrated (comprehensively and mutually compatible) and multi-modal, and includes a methodology for optimizing the balance of tradeoffs between geometric design elements and safety and operational performance for all users of these facilities.
The objective of this research is to develop a set of integrated guidelines that will help designers accomodate all users in the design of low- and intermediate-speed roadways, including:
  • Methods that can be used 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);
  • A methodology supported by empirically based research 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. 
Items to consider in the development of the guidelines should include:
  • Performance metrics addressing operations and safety; 
  • Best practices for developing design policies, including those of local government;
  • Best practices for implementation of multimodal projects;
  • “Complete streets”;
  • Constraints, e.g., right-of-way, roadside features, environmental, etc.;
  • Balance among principal elements of design;
  • Flexibility through:
    • Allocation of cross section design elements
    • Use of design exception process
    • Use of low cost options; 
  • Use of graphical illustrations;
  • User groups and their needs;
  • Use of TRB’s Highway Capacity Manual and AASHTO’s  Highway Safety Manual, including intermodal chapters; 
  • Use of geometric design and traffic control elements to create optimum roadway operation and safety for all users;
  • Consistency with AASHTO, TRB, and ITE references; 
  • Livable, sustainable communities; and 
  • Accessibility.
 A kick-off teleconference of the research team and NCHRP shall be scheduled within 1 month of the contract’s execution
The tasks must be divided into two phases. Phase I will consist of information gathering and planning tasks, culminating in the submittal of an Interim Report. The Interim Report will describe the work completed in the Phase I tasks and provide an updated work plan for the Phase II tasks. The updated Phase II work plan should address the manner in which the proposer intends to use the information obtained in Phase I to satisfy the project objective. A face-to-face Interim Meeting with NCHRP will be scheduled to discuss the Interim Report. Work on Phase II tasks shall not begin until the updated work plan is approved by NCHRP.   The project schedule should include 1 month for NCHRP review and approval of the Interim Report.
The research plan should include, but not be limited to:
  • A literature search
  • A survey of relevant agencies
  • Appropriate field investigations
A detailed description of any proposed survey or field investigation shall be submitted to NCHRP for prior review and comment.
The final deliverables shall include:
  • A final report documenting the conduct of the research
  • A standalone guidelines document

To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3416