The purpose of this investigation was to determine-the effects of selected roadway and operational characteristics upon accidents on multilane highways. Field data for 92 highway sites were collected and records of over 6000 accidents that occurred on these sites during a 21-month period in 1963 and 1964 were evaluated. Eight selected highway characteristics median width, speed limit, volume, level of service, access point index, intersection openings per mile, signalised openings per mile, and median openings per mile-- were correlated with all injury accidents on sites. A multiple regression analysis was performed so that the effects upon the accident frequency of all of the site characteristics could be examined simultaneously. By combining the five significant highway characteristics, a prediction equation to estimate injury accidents per mile was derived. An adjunct objective of determining the effects of the highway characteristics on the media opening accident rate was also considered. The Student's value which was calculated for each regression coefficients throughout the analysis indicates that, generally, as the magnitude of the variable increases, the median opening accident rate increases. This tends to support a rather widespread feeling among highway planners that the number of median openings of all types should be minimized. It is further concluded that whenever storage lanes are installed aft openings the median opening accident rate ills no longer significantly affected by (1) the number of openings excluding intersections, (2) the median width, (3) the speed limit, or (4) the traffic volume.
Abstract