Excessive speed is one of the most significant factors contributing to work zone crashes, which, along with work zone fatalities, have increased substantially in the past decade. From the beginning of 2000 to the end of 2003, the number of work zone crashes in South Carolina nearly tripled. In 2005, the South Carolina Department of Transportation initiated a research project to evaluate speed reduction measures in work zones. Through an in-depth literature review of speed control techniques for work zones, it was found that innovative technologies are often too expensive and thus impractical for large-scale implementation. There is a need for less-expensive technologies that are effective in reducing speeds in work zones. Development and evaluation of a speed-activated sign are discussed. Data were collected in work zones on two-lane primary and secondary highways in South Carolina, and the effectiveness of the speed-activated sign was evaluated on the basis of changes in mean speeds, 85th-percentile speeds, and percentages of vehicles exceeding the speed limit. Mean speed reductions ranged from 2 to 6 mph (3.2 to 9.7 km/h) with an average reduction of 3.3 mph (5.3 km/h). This average reduction improved to 4.1 mph (6.6 km/h) at sites where more than 50% of the vehicles were speeding before a sign was introduced. Further research was conducted with two speed-activated signs on a multilane divided highway and an Interstate freeway where similar speed reductions were experienced. From this study, researchers recommend that the speed-activated sign be used in short-term work zones.

Speeding through work zones is a major safety concern in South Carolina. Multiple traffic control devices aimed at reducing speeds in South Carolina work zones were evaluated. The majority of these speed control measures, with the exception of drone radar, were often found not to be practical for widespread, cost-effective implementation. The drone radar device has been tested for more than 20 years, though never before in South Carolina. The focus of this research was to determine the effect of drone radar as a speed reduction measure in work zones on Interstates and secondary highways during day and evening conditions, both for passenger cars and for tractor-trailers. One unique aspect of this study involves the use of a specialized detector to identify vehicles using radar detectors. Most documented research used visual inspection, which is not ideal for this determination, because many vehicles do not have their radar detectors in a visible location. The effectiveness of drone radar was evaluated on the basis of changes in mean speeds, 85th-percentile speeds, and percentage of vehicles exceeding the speed limit. Overall, drone radar caused mean speed reductions of 2 mph for the entire traffic stream. However, individual vehicles equipped with radar detectors reduced speeds ranging from 5 to 8 mph. Drone radar also caused 85th-percentile speeds to decrease between 1 and 5 mph, and a 20% speed reduction was shown in vehicles exceeding the speed limit.

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