8 Work Zone Safety

Impetus for the Activity

The States of Iowa, Kansas, Missouri and Nebraska formed the Midwest States Smart Work Zone Deployment Initiative to test and evaluate technologies for improving safety and efficiency of traffic operations in work zones. By working together, the agencies avoid unnecessary duplication of research through sharing of research results.

Criteria for System Selection (Hardware and Software)
The group held a series of three workshops to identify work zone problems, to define solutions and to select the technologies for evaluation. Potential solutions were presented by technology providers, and these solutions were matched with work zones on specific construction projects. The SpeedGuard System, provided by Speed Measurement Laboratories, was matched with work zones in Kansas and Nebraska.

Description of the System

The SpeedGuard system was deployed and evaluated during the 1999 construction season. The system is a speed monitoring system that measures vehicle speed and displays it, thereby hopefully warning drivers to slow down if they are speeding. The system is a portable trailer unit, and it measures vehicle speed using radar. Measured vehicle speeds are displayed on a panel with 61cm LED numerals. Power is provided by batteries, which are rated for 168 hours of use. The system is bulletproof and is camera-ready to allow photo enforcement (although this feature was not used here).

In Kansas, the system was deployed in a 8 km construction zone on rural I-70 in Wabaunsee County, about 50 km west of Topeka. ADT for the segment is 18,000 vehicles per day. The system evaluated had a strobe flash and an alarm horn. The evaluation team set the strobe flash to activate when the measured speed was above 103 km/h. The team set the alarm horn so that it would not activate. The purpose of the alarm horn is to warn workers in the work zone of an approaching vehicle that is traveling at an extremely high and potentially dangerous speed. The objectives of deploying the system were to reduce speeds in work zones and to reduce speed variance in work zones.

In Nebraska, the system was deployed on a rural I-80 work zone between Omaha and Lincoln. The segment has an ADT of 38,000 vehicles per day and the work zone speed limit was 89 km/h, a 32 km/h drop from the normal speed limit of 120 km/h. The deployed system had a “YOUR SPEED” sign posted below the display, and a “SPEED LIMIT 55” sign posted above the display. The objective of deploying the system was to reduce the speed of traffic and increase speed limit compliance.

System Performance

In Nebraska, the SpeedGuard unit malfunctioned after 7 hours and was removed from the site.

System Effectiveness Evaluation

The effectiveness of the SpeedGuard System was formally evaluated in both Kansas and Nebraska.

In Kansas, the evaluation team used a before and after study approach, using speed and speed distribution as the measures of effectiveness. The evaluation team found that the speed display resulted in a significant reduction in mean speeds, 85th percentile speeds, percent of drivers exceeding the posted limit, and speed variation. The evaluation team noted that the portability of the device, the ease of setup and the sturdy construction were advantages of the system, and that speed reductions resulting from the system were similar to those occurring during active law enforcement. Further tests are being conducted on the system in Texas and Kansas.

In Nebraska, the evaluation team found the SpeedGuard system to be effective in reducing speeds (by about 8 km/h) and increasing the uniformity of speeds. The team noted that the effects of the system on cars and trucks were similar, and that compliance with the speed limit increased to 90% or more. However, the team recommended additional studies due to the fact that the data was collected over the short 7-hour period when the system was functioning properly.

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