In an effort to relieve congestion on urban streets, bypasses have been built to provide through traffic a route by which the downtown areas can be avoided.

In many cases, though, bypasses have created a serious accident potential because they were built with at-grade intersections and no access control. This leads to commercial developments along the bypass and congestion at major intersections. Bypasses were constructed in this manner because of the high initial cost involved in building a bypass with access control and grade-separated interchanges. There is, therefore, a need to determine if the accident cost savings, along with time and operating cost savings, of a bypass with access control and interchanges would have justified the higher initial cost.

In this study, accident reports were obtained for several bypasses across the state and then analyzed to determine if they could have been prevented with the above mentioned controls. An accident was classified as "correctable" if it could have been prevented. Accident cost savings were then calculated using National Safety Council figures. Time and operating costs incurred by the motoring public as a result of stopping and returning to initial speed at the at-grade intersections, and conversely the benefits gained by building interchanges, were then calculated using tables which were based on traffic volumes and approach speeds at the intersections. Finally, using a study period of 20 years and a uniform-percentage-gradient series present-worth factor, the present worth of accident savings and time and operating cost savings were calculated. By comparing this savings with the initial cost of the construction of interchanges, benefit-cost ratios were calculated.

Report Date


Report Number

No. 341

Digital Object Identifier



The contents of this report reflect the views of the author who Is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Kentucky Department of Highways. This report does not constitute a standard, specification, or regulation.