BACKGROUND: In September 2018, the American Association of State Highway and Transportation Officials (AASHTO) published the 7th edition of A Policy on Geometric Design of Highways and Streets (also known as the 2018 Green Book). The 2018 Green Book provides guidance for determining geometric design criteria of roadways, including guidance on acceleration/deceleration and stopping sight distance criteria. Acceleration/deceleration is influenced by many factors (e.g., grade, vehicle type, and maneuver type). Stopping sight distance is influenced by many factors (e.g., perception reaction time, object height, and driver’s eye height). In addition, the recent changes in vehicle fleet, vehicle technology, and driver population impact the design criteria. Research is needed to identify the limitations of the 2018 Green Book guidelines for acceleration/deceleration and stopping sight distance criteria, develop improved guidelines, and recommend changes to the 2018 Green Book for consideration and adoption by AASHTO. Improved guidance could result in reduced environmental impacts, savings in construction costs, and reductions in construction time.
OBJECTIVE: The objective of this research is to update the guidelines for acceleration/deceleration and stopping sight distance criteria contained in the 2018 Green Book.
Accomplishment of the project objective will require at least the following tasks.
PHASE I: (1) Collect and review relevant domestic and foreign literature, research findings, and information relative to acceleration/deceleration and stopping sight distance criteria (e.g., vehicle fleet, vehicle technology, roadway alignment, pavement surface characteristics, vehicle operator, and climate). This information may be obtained from published and unpublished reports, and contacts with public and private organizations. (2) Based on the review performed in Task 1, identify the factors that are required for developing acceleration/deceleration and stopping sight distance criteria. (3) Evaluate the factors identified in Task 2 with consideration to safety performance, project type, context, and other relevant criteria, and identify those factors recommended for further consideration/investigation in Phase II. (4) Based on the evaluation performed in Task 3, prepare an updated, detailed work plan for Phase II that includes an approach for investigating the recommended factors and developing updated guidance on acceleration/deceleration and stopping sight distance criteria. (5) Prepare an interim report that documents the research performed in Tasks 1 through 4. Following review of the interim report by the NCHRP, the research team will be required to make a presentation to the project panel. Work on Phase II of the project will not begin until the interim report is approved and the Phase II work plan is authorized by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated work plan.
PHASE II: (6) Execute the Phase II plan approved in Task 5, and develop the updated guidelines for acceleration/deceleration and stopping sight distance criteria. (7) Prepare recommended changes to the respective sections of the 2018 Green Book for consideration and adoption by AASHTO. (8) Prepare a final deliverable that documents the entire research effort. The recommended changes to the 2018 Green Book shall be prepared as stand-alone document.
Status: Research in progress.
