NCHRP Research Results Digest 192: Procedure for Determining Work Zone Speed Limits, remains the definitive research regarding work zone speed limits. The digest, which resulted in the guidance in the current edition of the Manual on Uniform Traffic Control Devices (MUTCD), concluded:
- Mean speeds were approximately 5-mph lower within work zones with no speed limit reduction and that work zone speed limit reductions should be avoided, particularly where work activities are in shoulders or when no work activities are underway;
- A 10-mph reduction below the normal speed limit when work takes place on the traveled way or personnel are working in an unprotected position within 10 feet of the traveled way; and
- Work zone speed limit reductions greater than 10-mph should be avoided.
However, the research was completed in 1993 and is becoming increasingly dated. Notably, the repeal of the National Maximum Speed Limit (NMSL) during the study period, potentially influenced the conclusions and the recommended procedure. NCHRP Research Results Digest 192 notes that the NMSL produced poor compliance with the 55-mph speed limit and recognized that speed limit reduction also resulted in poor compliance while the level of speed limit compliance increased if the work zone speed limit was unchanged. These observations and conclusions should be verified or updated on present-day sites without the influence of the NMSL. Further, work zone technologies, policies, and practices have changed in the 29 years since the original research was completed. Examples include use of ITS technologies in work zones, emphasis on providing positive protection between road users and workers (23 CFR Part 630, Subpart K), law enforcement practices including automated enforcement, and others.
The objective of this research is to update the procedure for determining work zone speed limits by:
1. Collecting and analyzing work zone speed and crash data to test the conclusions from NCHRP Research Results Digest 192 to determine if present-day data verifies the conclusions or whether different conclusions are drawn from new data; and
2. Developing an updated procedure for determining work zone speed limits to be used for construction and maintenance operations and accommodate, to the maximum extent possible, the interests of motorists, workers, pedestrians, bicyclists, and transit operators and users.