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Research Projects (2007-08)

Identifying Number


Project Title

Evaluation of Optimal Traffic Monitoring Station Spacing on Freeways


University of Utah

Principal Investigator

Peter T. Martin

Description of Project Abstract

Performance measures on freeway travel are developed from traffic monitoring stations which gather volume and speed data. This data is used for several purposes: a) providing real-time speed on the website, which is color-coded based on three speed thresholds; b) calculation of real-time travel times, which is now posted on variable message signs (and which, in the future, will be placed on UDOT's CommuterLink website); and c) used for performance measure tracking. It is likely that other uses of speed data will be applied in the future, such as determining travel time reliability. UDOT has typically installed traffic monitoring stations at one-half mile intervals. This spacing dates back to theories that the traffic monitoring stations would be used to detect incidents in real-time. For example, Illinois DOT had such a system in place prior to the common use of cameras. Now, the use of cameras and cell phones has made the use of speed data for incident detection less important. The problem to be determined in this research is to evaluate the trade-off between detector spacing and accuracy of estimates I speed, travel time, and reliability.

Project Objectives

Develop recommended criteria for placement of speed detection stations on freeways, considering trade-off between spacing and accuracy.

Project Approach/Methods

Three types of training will be provided:

  1. Review existing UDOT data.
  2. Develop an analytical model or method to calculate travel time and travel time reliability measures based on hypothetical detector spacing.
  3. Using results of step 2, test alternative detector spacing to determine relationships between accuracy and spacing.
  4. Define recommended spacing.

Contributions/Potential Applications of Research

This will affect the location of traffic monitoring stations included in UDOT's ITS systems.

Technology Transfer Activities

If the conclusion is to increase the spacing (i.e. install fewer stations), there will be a cost savings.

Time Duration

July 1, 2007 – June 30, 2008

Annual and Total Project Cost

$30,206 Total: $60,412

TRB Keywords

Traffic monitoring, traffic congestion, traffic data

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050