In May 2013 the Texas State Legislature approved and required a pilot program to evaluate variable speed limits. Variable speed limits were piloted in areas identified as having conditions warranting temporary lower speed limits, including inclement weather conditions, congestion, and construction. Three sites were selected: westbound Loop 1604 in San Antonio, southbound I-35 in Temple, and I-20 in both directions at Ranger Hill in Eastland County.
Over the three month pilot period, there were over 400 activations of temporary speed limits, most commonly for congestion and least commonly for weather. Most activations lasted for less than an hour, but others lasted as long as 10 hours. Speed limits typically changed multiple times per activation.
Lessons learned during the three month pilot project in Texas included the following:
- Pavement friction sensors should target travel lanes instead of shoulder areas where wet pavement can persist causing VSL systems to reduce traffic speeds without need. Friction detectors were used to help determine speed limits during wet conditions, but they were typically pointed at the shoulder. If pointed at travel lanes regular speed limits may have been restored sooner because those lanes dried faster.
- Assure VSL signs that resemble fixed roadside speed limit signs have bright LEDs. During this pilot, the LEDs used to display speed limits had to be replaced shortly after deployment because they were not bright enough.
- If radar detectors and VSL signs are installed at the same location understand that the effects of the VSL system on traffic speeds may not be immediately detected which may affect system performance.
- Deploy cameras to verify the operation of VSL signs.
- Deploy failure resistant communication pathways to ensure consistent VSL operations.
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