Prepared by:

Jeffrey Suggett, M. Sc; B.E.S; B. Ed
Synectics Transportation Consultants

John McGill, P. Eng, P.T.O.E
Synectics Transportation Consultants

Abstract

High volume signalized intersections present a unique challenge to road safety practitioners. Signalized intersections by their very nature are risky because they require that different road users (vehicles, bicycles and pedestrians) use the same space and a crash is avoided only if they are separated in time. Signalized intersections have a larger number of possible conflict areas than other locations due to the unique array of movements required of its road users.

The soon to be released Federal Highway Administration (FHWA) publication “Signalized Intersection Guidelines” addresses each of these safety challenges. This publication will be a handbook for traffic engineers and other transportation officials on high-volume signalized intersections, their design, common operational and safety problems and their diagnosis.

The focus of this paper will be a description of how to diagnose and treat safety problems at high volume intersections. The guide describes using both a numerical and non-numerical approach for considering safety treatments. The numerical approach involves applying a collision modification factor or study result to the expected number of collisions to determine the safety benefit. The nonnumerical approach involves selecting a safety surrogate to assess a treatment using a safety risk index.
 

The guide makes the link between the diagnosis of safety to the selection of possible treatments. A number of chapters are devoted to possible treatments. These are organized into the following groupings: corridor treatments, intersection-wide treatments, approach treatments and individual movement treatments. Corridor treatments relate to the provision of a median, controlling driveway access and signal coordination. Intersection-wide treatments involve changes to the function of the traffic signal, pedestrian, bicycle and transit specific improvements, changes in alignment, intersection reconstruction and illumination. Approach treatments relate to traffic signal enhancements that provide better forewarning to approaching drivers as well as pavement, cross section and visibility improvements. Individual movement treatments (left, through and right turn) help to better and more safely accommodate each of these movements. Based on an extensive review of the state-of-thepractice, the FHWA handbook fully describes each treatment in terms of its current use, its possible application to a specific problem area, associated safety and operational issues, multimodal considerations, physical constraints, socioeconomic impacts and education/enforcement/maintenance issues.

For a complete copy of this paper, please contact: jsuggett@synectics-inc.net