In North Carolina, Portable Traffic-Monitoring Devices found to provide a cost-effective and safe means of recording speed and traffic counts in work zones.

Evaluation of PTMDs in work zones on I-95 and U.S. Route 64

June 11, 2010
Statewide; North Carolina; United States

Summary Information

Through its SafeTrip-21 initiative, the U.S. Department of Transportation (USDOT) is testing a variety of technologies along the Interstate 95 (I-95) corridor, a major north-south route on the east coast, and in a number of locations in California. As part of this Federal initiative, the North Carolina Department of Transportation (NCDOT) tested the use of portable traffic-monitoring devices (PTMDs) in work zones. The USDOT conducted an evaluation to learn how highly portable, temporary traffic sensors with a small footprint can provide real-time traffic conditions in work zones and to determine how that information can be used effectively by State Departments of Transportation (DOT) to improve safety and mobility in work zones.


The Evaluation Team conducted in-person interviews with NCDOT staff in December 2009 and follow-up telephone interviews with these staff to gain insight into their experiences with the PTMDs.


NCDOT staff reported that PTMDs provide situational awareness at a lower cost and with reduced highway agency staff exposure to traffic.

NCDOT's Resident Engineer informally tested the validity of the data by using the web interface to monitor the speeds through the work zones and then calling the inspector at the job site to determine if the PTMD speeds seemed reasonable. In his experience, the speeds reported by the PTMDs were accurate when compared to the general speed reported by the inspectors from their visual observations. In the future, NCDOT staff plan to compare the speeds from their PTMD applications with permanently installed ITS assets to more rigorously evaluate the device's accuracy. NCDOT staff felt confident the speed data were sufficiently accurate for their purposes.

NCDOT staff cited a number of benefits of the PTMDs, described below:
  • Accurate speed counts. Due to NCDOT's regular use of traffic drums in work zones, the PTMD was essentially invisible to the driver, mitigating data skewing that can occur when traffic-monitoring devices are conspicuously placed along a roadway. Speed data reported was confirmed with inspector on site.
  • Ease of installation and operation. NCDOT staff reported that installation was straightforward. Since the PTMD is powered by battery, communicates via cellular or satellite communications, and looks like a traditional work zone drum, the device was able to be placed anywhere a work zone drum would be placed.  Data is presented through a web-based user interface which can be accessed from the office or home.
  • Data warehousing capability. Beyond the ability to access traffic data in real-time, NCDOT staff indicated long-term data warehousing as a significant benefit of the web-based database the PTMDs generate. The web site for the PTMDs stores and archives the data for 5 years, giving NCDOT staff the flexibility to analyze historical data.
  • Safety benefits. PTMDs allowed personnel to collect traffic volume data without requiring them to work in the travel lane, reducing injuries.
  • Staff Productivity. Instead of visiting work sites, the Resident Engineer (RE) and other personnel were able to use the PTMDs to gain an awareness of the traffic situation in their work zones remotely.

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National Evaluation of the Safe Trip-21 Initiative: I-95 Corridor Coalition Test Bed, Final Evaluation Report: North Carolina Deployment of Portable Traffic-Monitoring Devices

Author: Chandler, B., Beasley, K., & Rephlo, J.

Published By: FHWA, USDOT

Source Date: June 11, 2010



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Typical Deployment Locations

Rural Areas, Statewide


smart work zone systems, smart work zone, smart work zones, Smart work zones, workzone, WZ, work zone, PTMD

Benefit ID: 2013-00860