This is an evaluation of the Visual Speed Indicator (VSI) an electronic traffic sign which calculates and displays the speeds of vehicles which pass it: The sign employs a warning message, "SLOW DOWN," which is flashed when a vehicle's speed exceeds a pre-set threshold, which in this case was the posted speed limit. The goal of the device is to reduce the variability of speeds about the mean speed on a given roadway, especially those speeds in the upper end of the distribution. It was hypothesized that such an effect would take place after viewing the operation of the sign and would last for a minimum distance of two miles downstream. To evaluate the effectiveness of the sign, an experimental design was developed whereby speed data were continuously collected on cassette (data) tape during four time periods. Period 1 was used to gather baseline data before the sign was installed. During Period 2, the sign was activated. In Period 3, the VSI was deactivated and covered. Finally, during period 4, the sign was again activated. The section of roadway chosen for the experiment was a two-lane rural roadway with a volume of approximately 3,000 vehicles per day. Three sites were selected, each speed approximately two miles apart, for the installations of data collection equipment. The sign itself was installed at the middle site (Site 2) after Period 1 and before the beginning of Period 2. In addition to various descriptive statistics, the data were analyzed using a multivariate general linear model (NGLM) computer program. Linear models were fitted to the three different dependent variables of mean speed, speed variance, and percentage of traffic speeding. The results indicated that there were significant reductions in both the mean speed and percentage of traffic speeding at the location of the sign after the sign was activated, when compared with the upstream control location. However, these effects were dissipated within two miles, in that they did not carry over to the downstream location. The speed variance increased significantly at the sign location after the sign was activated, and the change at the downstream location was not significant when compared with the upstream control location. These findings concerning speed variance were counter to what was expected of the sign. /Author/

  • Supplemental Notes:
    • Sponsored by North Carolina Office of the Governor's Highway Safety Coordinator.
  • Corporate Authors:

    University of North Carolina, Chapel Hill

    Highway Safety Research Center
    Chapel Hill, NC  United States  27599
  • Authors:
    • Hunter, W W
    • Bundy, H L
    • Daniel, R B
  • Publication Date: 1976-4

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 90 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00141770
  • Record Type: Publication
  • Source Agency: National Safety Council Safety Research Info Serv
  • Files: TRIS
  • Created Date: May 31 1977 12:00AM