Safety Evaluation of Multiple Strategies at Stop-Controlled Intersections

Chapter 1. Introduction

Background on Multiple Strategies at Stop-Controlled Intersections

In recent years, there has been an increased interest in systemic installations of low-cost safety treatments throughout an entire jurisdiction. The South Carolina Department of Transportation (SCDOT) embraced this approach in its intersection safety improvement plan and identified a number of low-cost strategies for implementation at stop-controlled and signalized intersections statewide. Typical low-cost treatments at stop-controlled intersections in South Carolina included improvements to basic signing and pavement markings. Figure 1 illustrates typical improvements at a four-legged, stop-controlled intersection with two-lane major road.

© SCDOT.
Figure 1. Illustration. Example of stop-controlled intersection improvements.

The following is an overview of the types of basic signing and pavement markings improvements, and the appendix provides further details and considerations. Each treatment was installed when appropriate. Each intersection received a unique package of improvements suited for implementation at that site, which included the following:

• Signing improvements included the following:
  
  
  • Double-up (i.e., both right- and left-side, shoulder mounted) 36 inches by 36 inches intersection warning signs (W2-series) on fluorescent yellow sheeting. Figure 1 shows examples of applicable intersection warning signs for stop-controlled intersections.
    
    
  • Advance street name plaque (W16-8) on fluorescent yellow sheeting accompanying each right-side intersection warning sign.
    
    
  • Double-up (i.e., both right- and left-side, shoulder mounted) 48 inches by 48 inches stop (R1-1) and yield (R1-2) signs.
    
    
  • Retroreflective strips on sign posts for the above signs.
    
    
• Pavement marking improvements included the following:
  
  
  • Stop lines within 4 to 10 ft of the edge of the nearest through lane along the major road.
    
    
  • Yield lines at all lanes having yield conditions.
    
    
  • Dashed white edge-lines through intersections along major roads.
    
    
  • Remarking of all existing stop lines, crosswalks, arrows, and word messages unless:
    • The roadway had been resurfaced within one calendar year and new thermoplastic markings had been applied.
      
      
    • Existing markings were uniformly reflective, and the above ground thickness was 90 mm or greater.
      
      
    • Otherwise directed by a district representative.
      
      
  • Marking of all turn lanes to include the pattern of lane arrows and accompanying word message “ONLY” based on the turn-lane length, in accordance with Standard Drawing 625-410-00.

Background on Study

The goal of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI-PFS) is to develop reliable estimates of the effectiveness of the safety improvements that are identified as strategies in the National Cooperative Highway Research Program (NCHRP) Report 500 Guides.⁽¹⁾ These estimates are determined by conducting scientifically rigorous evaluations at sites in the United States where these strategies are being implemented. The study has spanned multiple phases. In March 2005, the first Technical Advisory Committee Meeting of the ELCSI-PFS was held at the Turner-Fairbank Highway Research Center. The purpose of the meeting was to discuss the study and applicable strategies from the NCHRP Report 500 Guides and to develop a prioritization of those strategies for potential evaluation in the study.⁽¹⁾ Since this initial meeting, several phases have been undertaken to evaluate strategies.

Phase V of the ELCSI-PFS is a “build-to-evaluate” effort in which States have volunteered to install a variety of promising low-cost safety countermeasures and contribute the appropriate data to allow a rigorous crash-based evaluation of their safety effectiveness. This phase has a two-part nature and consists of an implementation part and an evaluation part. The implementation portion (Part 1) defined the before period, including installation data (location and date), roadway data, traffic data, and crash data. The evaluative portion (Part 2) began within 3 years of the conclusion of the installation phase. Four safety strategies were identified for implementation and evaluation in Phase V. Five States volunteered and provided data for the Phase V evaluations. Table 1 shows these safety improvement strategies and the volunteering States.

—Not used.

As a volunteering State, SCDOT initiated a project to improve safety at more than 2,200 intersections statewide through low-cost engineering techniques focused primarily on signing and markings in 2009. These intersections—600 of which were classified as rural—comprise only 2 percent of all State-maintained intersections but account for nearly half of all intersection crashes and fatalities. It was envisioned that the project would span 3 years and implement improvements at approximately 700 to 800 intersections each year.

This report documents the safety effectiveness evaluations of multiple strategies at stop-controlled intersections implemented in South Carolina. The evaluation of multiple strategies at signalized intersections can be found in the companion report entitled Safety Evaluation of Multiple Strategies at Signalized Intersections.⁽⁶⁾