Advance Warning of Stopped Traffic on Freeways: Summary of Project Activities (0-4413-S)

Stopped traffic on freeways poses safety and operational concerns to drivers, transportation agencies, construction and maintenance contractors, and enforcement and emergency service personnel. Safety issues relate to driver ability to make gradual transitions from freeway speeds to stopped conditions without erratic maneuvers or crashes. Operational concerns relate to the reliability and predictability of the freeway network. The primary type of multi-vehicle crash on a freeway facility is the rear-end collision, comprising over 50 percent of freeway crashes by some research findings, caused generally due to normal speed traffic encountering stopped traffic on the main lanes or ramps. Drivers frequently have minimal or no warning about downstream queuing, and information given on static signs is difficult to keep current with rapidly fluctuating queues in congested areas. Stopped traffic on the freeway may be due to a multitude of causes. This research project evaluated issues relating to stopped or very slow traffic due to three major causes: recurrent traffic congestion due to over-capacity conditions during peak periods, congestion due to construction and maintenance work zones, and congestion due to incidents such as crashes. In the first phase of this project, the research team conducted a literature review to determine current practices for advance warning for stopped traffic, observed field locations with traffic stopped due to various conditions, and determined advance warning techniques applicable to Texas. Report 4413-1 presents this information. In the second phase of this project, researchers tested two advance warning techniques using static warning signs on Dallas area freeways. The research team synthesized the field test results and developed recommendations for further research and ways to improve the signing. This information is presented in this report. Many factors remain to be addressed in future research; however, observations conducted in this project can provide guidance to those testing and implementing operating systems for advance warning of slow/stopped traffic on freeways.