Development and Evaluation of Speed-Activated Sign to Reduce Speeds in Work Zones

Excess speed is one of the most significant factors contributing to work zone crashes, which, along with work zone fatalities, have increased substantially in the last 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 (SCDOT) initiated a research project to evaluate speed reduction measures in work zones. Through an in-depth literature review of work zone speed control techniques, researchers found that new innovative technologies are often too expensive, making them impractical for large-scale implementation. Thus, there is a need for less expensive technologies that are effective in reducing speeds in work zones. This paper discusses the development and evaluation of a speed-activated sign. 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 based on 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 kph) with an average reduction of 3.3 mph (5.3 kph). This average reduction improved to 4.1 mph (6.6 kph) at sites where more then 50 percent of the vehicles were speeding prior to introduction of the sign. Further study was conducted using two speed-activated signs on a multi-lane divided highway and an interstate freeway where similar speed reductions were experienced. From this study, researchers recommend the speed-activated sign be used in short-term work zones.