At a work zone in South Dakota, a speed monitoring and display system reduced the number of speeding passenger vehicles and trucks by as much as 25 and 40 percent respectively.

Experience with speed warning displays at work zones in South Dakota

Sioux Falls; South Dakota; United States

Summary Information

This study evaluated the effectiveness of a vehicle speed warning system at reducing traffic speeds approaching a bridge replacement work zone on westbound Interstate 90 near Sioux Falls, South Dakota. The system used radar to detect vehicle speeds approaching the work zone and then posted vehicle speeds on two portable speed monitoring displays installed about 310 ft in advance of the work zone lane closure taper. The displays were positioned at the edge of the shoulder on each side of the roadway.

Traffic data were collected before and after the speed monitoring displays were installed. Vehicle speed, traffic volume, headway, and classification data were collected using tape switches installed in the roadway at three locations (stations):
  • Station 1 was located about 4,000 ft in advance of the lane closure taper and 650 ft downstream from a static message sign indicating "ROAD CONSTRUCTION AHEAD."
  • Station 2 was located at the beginning of the lane closure taper.
  • Station 3 was located at the end of the taper.

On Monday, July 12, 1993 the "before" data were collected, on Tuesday, July 13, 1993 the speed monitoring displays were installed, and on Tuesday, July 20, 1993 the "after" data were collected. The "before" data included: 2118 measurements at Station 1; 1,599 measurements at Station 2; and 1,551 measurements at Station 3. The "after" data included: 1,980 measurements at Station 1; 1,478 measurements at Station 2; and 1,428 measurements at Station 3.


Analysis of the vehicle types (number of axles) data and the traffic volume data indicated the influence of these factors could be applied equally to the before and after data, thus the author was able to compare the before and after data using the least-square method. The results of the analysis indicated that the speed monitoring displays reduced the mean speed of traffic by 4.7 mi/hr at Station 2 and by 3.8 mi/h at Station 3.

Accounting for variability in the data, the author indicated that the speed monitoring displays were able to reduce average traffic speed by 4 to 5 mi/h. After the speed monitoring displays were installed, the number of two-axle vehicles exceeding the advisory speed limit (45 mi/h) by more than 10 mi/hr decreased by about 20 to 25 percent at Stations 2 and 3. The number of vehicles with more than two axles traveling at excessive speeds at these two locations dropped by about 40 percent.

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Speed Reduction Effects of Speed Monitoring Displays with Radar in Work Zones on Interstate Highways

Author: McCoy, P.J., J.Bonneson, and J. Kollbaum

Published By: Transportation Research Record

Source Date: 1995

Other Reference Number: TRR 1509



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Goal Areas



smart work zone systems, smart work zone, smart work zones, Smart work zones, workzone, WZ, automated enforcement, Smart work zone

Benefit ID: 2007-00329