1971 VIRGINIA LICENSE PLATE STUDY: POWERFUL OR WEAK EXPERIMENTAL DESIGN

In January 1974, Charles B. Stoke, a highway research analyst with the Virginia Highway Research Council, issued a final report based on the study entitled; Reflectorized license plates: Do they reduce nighttime rear-end collisions?" In his report Mr. Stoke concluded that there was no statistically significant difference between the number of nighttime rear-end collisions of vehicles equipped with reflectorized license plates and that of vehicles equipped with control non-reflectorized license plates. The conclusions from Mr. Stoke's report are in conflict with the results of the earlier reflectorized license plate studies. These previous studies acknowledged a safety benefit for vehicles equipped with reflectorized license plates through reductions in the frequency of nighttime rear-end collisions. The present report is a critical review, analysis, and evaluation of Mr. Stoke's methodology, data and conclusions. The present authors, after analysis and evaluation of Mr. Stoke's final report and the related data, found that Mr. Stoke's conclusions were not supported by the full accident data which were available to him. The limited sample size employed by Mr. Stoke resulted in the conduct of an exceptionally weak experiment. That is, the experimental design was so weak that practically significant differences (which were found) were not also statistically significant. Other data in the reports analyzed strongly indicate that reflectorized license plates were effective in reducing nighttime rear-end collisions. Although the present investigation and report focused on Mr. Stoke's final report and the nighttime accident reduction potential of reflectorized license plates, a great deal of the discussion in the present report is relevant to a variety of decision-making situations both in and out of the realm of highway safety.

  • Corporate Authors:

    University of South Carolina, Columbia

    Traffic and Transportation Center
    Columbia, SC  USA  29208
  • Authors:
    • Kleinknecht, R E
    • Hicks, J A
  • Publication Date: 1974

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 18 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00097169
  • Record Type: Publication
  • Source Agency: Highway Safety Research Institute
  • Files: TRIS
  • Created Date: Sep 10 1975 12:00AM