License plate recognition system successful in monitoring travel times, leading to reduced congestion in work zone.

October 2004
Kingman,Arizona,United States

Summary Information

The case study describes the experience of the Arizona Department of Transportation (ADOT) using Intelligent Transportation Systems (ITS) to support work zone operations during the reconstruction and widening of State Route 68 (SR 68) in northern Arizona. ADOT included an incentive/disincentive provision in the project contract to encourage the contractor to minimize work zone delays.

ADOT required the contractor to acquire a system for measuring travel time through the work zone and report average travel time in 30-minute periods. The contractor chose a camera-based license plate matching system that took pictures of vehicle license plates entering and leaving the work zone. The system then used those images to determine average vehicle travel times through the work zone. The contractor could earn a potential $400,000 bonus incentive for maintaining adequate traffic flow at the target of 27 minutes. For each 30-minute time period the work zone was in place, each minute delay above the target resulted in a fine of $21.50 for the contractor.


This case study presents information gathered through interviews with key personnel on the Arizona SR 68 project in Kingman, Arizona, as well as information and photographs obtained during a site visit.


The use of an ITS application on SR 68 in Arizona was a success. The contractor was able to maintain traffic flow through the project according to the ADOT time-specified requirements. The contractor was charged only $14,857 against the $400,000 travel time bonus, thereby earning 96 percent of the bonus fund.

With the use of the travel-time system and the incentive/disincentive clause, the contractor was forced to be innovative in managing construction efforts to minimize impact on the traveling public. ADOT reported the following benefits:
  • The system was able to read approximately 60 percent and match approximately 11 percent of the license plates photographed during the operation. ADOT considered this an adequate level of performance to compute average travel times and compared to other license plate detection systems.
  • The contractor responded to the knowledge that the travel time incentive/disincentive clause would be enforced by limiting the number of flagging stations in the work zone and by limiting the duration of directional closings to two to three minutes at most.
  • The contractor worked with ADOT to schedule work periods to reduce adverse impact on motorists. Since this area had no established morning or afternoon peak traffic times, the contractor and ADOT studied traffic volumes and surveyed employers to determine the best time for lane shifts.
  • A secondary benefit was reduced exposure of workers to traffic. The contractor scheduled work in close proximity to travel lanes during periods of low traffic volume to minimize delays.
  • Overall, the contractor felt that the knowledge that work zone delays were being monitored by the time-travel system forced the crew to pay closer attention to the impacts that their construction would have on the traveling public.
Finally, ADOT received a great deal of positive feedback from the public through e-mails and letters of appreciation. The public seemed genuinely pleased that delays were not as severe as expected.

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Intelligent Transportation Systems in Work Zones: A Case Study - Work Zone Travel Time System

Author: Tracy Scriba, Jennifer Rephlo

Published By: U.S. Department of Transportation Intelligent Transportation Systems Joint Program Office Federal Highway Administration

Source Date: October 2004

EDL Number: 14001



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Goal Areas


Typical Deployment Locations

Rural Areas


smart work zone systems, smart work zone, smart work zones, Smart work zones, workzone, WZ, CCTV, closed circuit television cameras, road monitoring, sensors, vehicle detector, traffic detection, traffic monitoring, congestion monitoring, ITS, license plate recognition system, license plate matching system, incentive/disincentive program, contract incentive

Benefit ID: 2010-00641