Despite a national standard on the uniform application of centerlines, lane lines, and edge lines—which is designed to promote highway safety and efficiency—every 21 minutes a highway death occurs from a lane departure. While there is a national effort to keep drivers on the road, and pavement marking is one potential countermeasure (with an estimated annual expenditure in the United States of $2 billion), there is a need for a consolidated effort to bring together recent and ongoing research findings demonstrating a renewed perspective on the benefits of pavement markings.
Crashes
Almost all the recent crash research has been geared toward adding edge lines to highways. Recent crash studies as well as those more than a half century old have conclusively shown that adding edge lines to rural two-lane highways can reduce crashes and fatalities. Some of the findings demonstrate that these benefits can be achieved with narrow pavement widths (18 feet or less) and low ADTs (as low as 1,000 vpd). The benefits have been shown to be statistically significant in areas of all terrain types, and in all locations during nighttime conditions and nighttime low-visibility conditions.
In terms of vehicle speeds and lateral placements, there appears to be either no real impacts or, at most, only subtle impacts as a result of adding edge line markings. This includes narrow two-lane highways and day and night conditions.
In a recent study, driver workload was reduced after edge lines were added to narrow two-lane highways.
Wide Markings
Earlier crash studies conducted on wider pavement markings were inconclusive, showing no particular benefit. However, current research using the latest statistical analysis techniques is showing the potential benefit of wider pavement markings on rural two-lane highways. For instance, edge line width has been found to statistically lower nighttime fatal and injury crashes in an ongoing analysis of two state’s data, which is particularly useful since the nighttime crash rates is approximately three times higher than the daytime crash rate.
These new safety findings, though, are not supported by the latest visibility research, which has shown inconsistent findings related to increased detection distances from wider markings. The expectations are high for ongoing research to demonstrate how wider markings can lower crash rates. Using state-of-the-art eye-tracking equipment in an instrumented vehicle, researchers are currently evaluating how drivers use markings through both the foveal and peripheral vision system.
Retroreflectivity
While the FHWA works to develop minimum maintained retroreflectivity levels for pavement markings (55), several agencies have conducted subjective evaluations of their roads and pavement markings to identify what drivers think they need. Having highly visible pavement markings is a high-ranking desire among the public. It also appears that the public prefers to have their markings maintained to at least 80 to 130 mcd/m²/lx.
Research is currently underway to assess whether DOT personnel can adequately judge marking retroreflectivity during nighttime visual inspections. This will be a key element of managing retroreflectivity in terms of maintaining adequate levels of retroreflectivity for safe nighttime driving.
The correlation between retroreflectivity and crashes has been a topic of recent research. Several efforts have been completed to identify a statistical correlation, but no conclusive evidence has yet to be generated. Each effort has been unique and innovative in terms of the study approach, but they either used assumed or modeled retroreflectivity data, or retroreflectivity data that were measured but much higher than what has been judged to be a preferred minimum, 80 to 130 mcd/m²/lx. Continued research using measured retroreflectivity data and advanced analysis techniques is generating promise in terms of identifying the elusive correlation between retroreflectivity and crashes.