CTRE is an Iowa State University center, administered by the Institute for Transportation.

Address: 2711 S. Loop Drive, Suite 4700, Ames, IA 50010-8664

Phone: 515-294-8103
FAX: 515-294-0467

Website: www.ctre.iastate.edu/

Iowa State University--Becoming the Best

Evaluation of Electronic Speed Limit Signs for Unified Consolidated School on US 30, Eastbound and Westbound

Dynamic, electronic school zone speed limit sign at United Community Schools on US 30


Principal investigators:

Student researcher:

Project status


Start date: 10/01/07
End date: 09/06/11


Report: Evaluation of Electronic Speed Limit Signs on US 30 (1.98 mb pdf) September 2011



About the research


This study documents the speed reduction impacts of two dynamic, electronic school zone speed limit signs at United Community Schools between Ames and Boone, Iowa. The school facility is situated along US Highway 30, a rural four-lane divided expressway.

Due to concerns about high speeds in the area, the Iowa Department of Transportation (DOT) decided to replace the original static school zone speed limit signs, which had flashing beacons during school start and dismissal times, with electronic speed signs that only display the reduced school speed limit of 55 mph during school arrival and dismissal times.

The Center for Transportation Research and Education (CTRE) at Iowa State University (ISU) conducted a speed evaluation of the area one week before and then 1 month, 7 months, and 14 or 15 months after the new signs were installed.

Overall, the new dynamic school zone speed limit signs were more effective in reducing speeds than the original static signs with flashing beacons in the 1 month after period. During the 7 and 14 month after period, speeds increased slightly for the eastbound direction of traffic. However, the increases were consistent with overall speed increases that occurred independent of the signs.

The dynamic, electronic signs were effective for the westbound direction of traffic for all time periods and for both start and dismissal times. Even though only modest changes in mean and 85th percentile speeds occurred, with the speed decreases, the number of vehicles exceeding the school speed limit decreased significantly, indicating the signs had a significant impact on high-end speeders.