Systemwide Analysis of Freeway Improvements

Abstract

Determining where to restripe or widen freeway sections to strategically relieve bottlenecks is a far more complicated problem than simply estimating the local capacity effects of specific lane additions. The pros and cons of reducing lane and shoulder widths to obtain an extra travel lane are discussed, with an emphasis on the effects on the overall freeway system. This study describes how increasing capacity at an upstream location can overload a downstream bottleneck and cause flow breakdown. An evaluation of potential local improvements at a number of existing bottlenecks in the westbound Highway 401 corridor in Toronto is provided; it finds that in a systems context about one-half are worthwhile, and the others have net negative effects.

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