Safety Evaluation of Wet-Reflective Pavement Markings

Chapter 2. Objective

This research examined the safety impacts of wet-reflective markings in Minnesota, North Carolina, and Wisconsin. The objective was to estimate the safety effectiveness of this strategy as measured by crash frequency. Intersection-related, animal-related, and ice/snow/sleet-related crashes were excluded. The following target crash types were considered:

• Total crashes (all types and severities combined).
  
  
• Injury crashes (K, A, B, and C injuries on the KABCO scale, where K is fatal injury, A is incapacitating injury, B is non-incapacitating injury, C is possible injury, and O is property damage only).
  
  
• Run-off-road crashes (all severities combined).
  
  
• Head-on crashes (all severities combined).
  
  
• Sideswipe-opposite-direction crashes (all severities combined).
  
  
• Sideswipe-same-direction crashes (all severities combined).
  
  
• Wet-weather crashes (all types and severities combined).
  
  
• Nighttime crashes (all types and severities combined).
  
  
• Nighttime wet-weather crashes (all types and severities combined).

The effects for dry-road crashes, which were not specifically evaluated as a target crash type, were inferred from the effects for total and wet-road crashes.

A further objective was to address questions of interest such as the following:

• Do effects vary by roadway type?
  
  
• Do effects vary by level of traffic volumes?
  
  
• Do effects vary by posted speed limit?
  
  
• Do effects vary by horizontal curvature?
  
  
• Do effects vary by shoulder width?
  
  
• Do effects vary by lane width?
  
  
• Do effects vary by the site-specific expected crash frequency prior to treatment?
  
  
• What is the overall effect, measured by the economic costs of crashes by crash type and severity?
  
  
• What is the B/C value?

The evaluation of overall effectiveness included consideration of the installation costs and crash savings in terms of the B/C ratio.

Meeting these objectives placed some special requirements on the data collection and analysis tasks, including the following:

• Select a large enough sample size to detect, with statistical significance, what may be small changes in safety for some crash types.
  
  
• Identify appropriate untreated reference sites.
  
  
• Properly account for changes in safety due to changes in traffic volume and other non-treatment factors.
  
  
• Pool data from multiple jurisdictions to improve reliability of the results and facilitate broader applicability of the products of the research.