AN IMPROVED BRIDGE SAFETY INDEX FOR NARROW BRIDGES

An improved safety index model is developed for narrow bridges by using data collected on 78 bridges in Texas by the Texas Transportation Institute. Cluster analysis was used to classify the bridges into more-safe and less-safe groups. Correlation and factor analyses were used to find the interrelationships between the independent variables of bridge and approach roadway characteristics. Stepwise regression was used to find the most important variables related to accident rate. On the groups developed by cluster analysis, logistic regression was used to develop a model that is a function of several variables that were found to be significantly related to accident rate. The enhanced safety index model consists of the following variables: bridge width, length, average daily traffic, and speed, as well as the subjective safety factors F6 (grade continuity), F7 (shoulder reduction), and F9 (traffic mix). The model was arrived at scientifically by using more objective procedures of classification and by having a stronger correlation with the accident rate than the previous models used by other researchers. The fewer variables used yield a much higher R2 when accident rate is used as the response variable in multiple regression. It is sensitive to changes or improvements in the constituent factors. The model yields the fraction of concordant pairs of predicted probabilities and responses as 0.91 and a high rank correlation of 0.81 between predicted probability and response, which indicates the goodness of the model. It also gives the safety index directly and can be used to identify a potentially hazardous narrow bridge.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1984/960/960-006.pdf
• Summary URL:
  • https://scholar.google.com/scholar_lookup?title=AN+IMPROVED+BRIDGE+SAFETY+INDEX+FOR+NARROW+BRIDGES&author=R.+Lytton&author=B.+Das&publication_year=1984
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/03611981
• Supplemental Notes:
  • Publication of this paper sponsored by Committee on Operational Effects of Geometrics. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Lytton, Robert L
  • Das, Biman
• Conference:
  • 63rd Annual Meeting of the Transportation Research Board
  • Location: Washington District of Columbia, United States
  • Date: 1984-1-16 to 1984-1-20
• Publication Date: 1984

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 40-48
• Monograph Title: GEOMETRICS AND SAFETY CONSIDERATIONS
• Serial:
  • Transportation Research Record
  • Issue Number: 960
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Average daily traffic; Bridge approaches; Cluster analysis; Crash rates; Forecasting; Hazards; Identification systems; Mathematical models; Narrow bridges; Safety; Safety factors; Traffic speed
• Uncontrolled Terms: Identification; Models; Safety index
• Subject Areas: Design; Highways; Operations and Traffic Management; Safety and Human Factors; I81: Accident Statistics;

Filing Info

• Accession Number: 00391643
• Record Type: Publication
• ISBN: 0309037069
• Report/Paper Numbers: HS-038 213
• Files: HSL, TRIS, TRB
• Created Date: Aug 31 1985 12:00AM