Citation

Lu XY, Shladover S. Transp. Res. Rec. 2014; 2423: 15-23.

Copyright

(Copyright © 2014, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.3141/2423-03

PMID

unavailable

Abstract

Previous studies on variable speed limits (VSLs) were reviewed. These studies were classified as three types: simulations for algorithm development and evaluations, VSL implementation and field testing, and a combination of VSLs with ramp metering. The review considered strategies and algorithms, targeted traffic improvements (safety, throughput, etc.), applicable traffic conditions, performance evaluations, and simulation or test results and their implications. Most practices in Europe indicated that the use of VSLs was effective in both traffic safety and flow improvement, although the former was more significant. Practices in the United States indicated that safety improvement was significant but the impact on traffic flow was controversial. Practices are summarized, and some new viewpoints and future research directions are presented.