Proposing New Advisory Speeds in Mountainous Areas Considering the Effect of Longitudinal Grades, Vehicle Characteristics, and the Weather Condition

Speed limits play a pivotal role in traffic safety on mountainous roadways. Due to Wyoming’s unique conditions, designing mountainous roadways with appropriate design speeds is challenging. These roadways are characterized by adverse weather conditions and tight horizontal curves with steep downgrades or vertical curves (combined horizontal and vertical curves). Skidding and rollover toward the outer direction of the curve are the main threats on these curves. The current speed limit design policy in the Green Book (AASHTO 2011) obtained from the design of the horizontal curve does not account for these challenges and has shortcomings. This research aims at evaluating the appropriateness of the posted speed limits and vehicle stability on Wyoming’s hazardous curves. This research also intends to propose a new design framework to set speed limits on combined curves with respect to vehicle stability. Therefore, a high-fidelity dynamic simulation modeling approach was used to assess lateral and roll stability of different vehicle types on various road surface conditions. The results showed that the current speed limits are unsafe and should be modified under some circumstances. Vehicle stability significantly changes based upon the vehicle type and configuration coupled with weather conditions, and therefore appropriate speed limits vary accordingly. The developed models of skidding margins (SMs) and rollover margins (RMs) quantify accurately the impact of the geometric and environmental characteristics on the vehicle performance when cornering. The proposed framework and assessment will assist Wyoming’s roadway authorities in imposing more appropriate speed limits for vehicles on hazardous sections based on the weather conditions and vehicle configurations. Furthermore, the results would be beneficial for companies developing automated trucks.

• Record URL:
  https://www.ugpti.org/resources/reports/details.php?id=1085
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/63600
• Summary URL:
  https://rosap.ntl.bts.gov/view/dot/67974
• Supplemental Notes:
  • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  University of Wyoming, Laramie

  Department of Civil and Architectural Engineering
  1000 East University Avenue
  Laramie, WY  United States  82071

  Mountain-Plains Consortium

  North Dakota State University
  Fargo, ND  United States  58108

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Authors:
  • Alrejjal, Anas
  • Ksaibati, Khaled
• Publication Date: 2022-7

Language

• English

Media Info

• Media Type: Digital/other
• Features: Appendices; Figures; References; Tables;
• Pagination: 96p

Subject/Index Terms

• TRT Terms: Highway curves; Mountain roads; Rollover crashes; Skidding; Speed limits; Stability (Mechanics)
• Geographic Terms: Wyoming
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01857399
• Record Type: Publication
• Report/Paper Numbers: MPC-22-457
• Contract Numbers: MPC-574
• Files: UTC, NTL, TRIS, ATRI, USDOT
• Created Date: Sep 12 2022 10:18AM