It is evident from this paper that the arena of pavement marking research is active and delivering findings demonstrating the effects of pavement markings and their characteristics. Despite the new and exciting findings, it also appears obvious that more work is needed and opportunities exist to develop safety-based policies and performance-based specifications.

For instance, there is an excellent opportunity to investigate how the MUTCD pavement marking warrants could be modified based on safety-supported criteria. Speed is not currently considered in the criteria. What if the policy on pavement marking applications was tied to minimum retroreflectivity levels in a way that provides a synchronized approach so that higher-speed roadways have higher requirements of retroreflectivity (to provide drivers with adequate preview times from low-speed to high-speed roadways)?

Another area of needed research is thorough analyses of crashes by key factors such as pavement marking presence, lane widths, ADT, functional classification, curve presence, and volume. This should include state and local roadways. The results of thorough analyses could be used to support changes to the MUTCD policies that would provide safety-supported policies for when to apply pavement markings.

Continued work is needed to develop a correlation between retroreflectivity and safety. Although existing work is ongoing, the task is challenging. A key component of having a successful effort is having rich data sources. In this case, there needs to be a rich data source for both crashes and measured pavement marking retroreflectivity. The most challenging item is having retroreflectivity data that are reliable and represent the condition of the pavement marking during crash periods.

Another area of research that is potentially rich with information is further study of how drivers use pavement markings during daytime and nighttime conditions. More information is needed to better understand how driving behavior shifts during low-visibility conditions, when negotiating horizontal curves, or when oncoming traffic approaches at night.

There are many advances underway. Pavement marking technologies are producing more durable markings, brighter markings, and markings that continue to retroreflect even during rainy conditions. Agencies are continuing to use pavement markings on rumble strips for added visibility and durability. Many agencies are developing successful pavement marking management tools that include innovative performance measures. The specifications for pavement markings are also evolving to accommodate new technologies and innovative pavement marking management practices. These efforts, and others, have been shown to be effective. As noted earlier, the Missouri Department of Transportation has seen a 25 percent reduction in lane departure crashes since implementing policies to help keep drivers on the road.