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Journal Article

Citation

Lenters M, Rudy C. ITE J. 2010; 80(7): 22-27.

Copyright

(Copyright © 2010, Institute of Transportation Engineers)

DOI

unavailable

PMID

unavailable

Abstract

The 2010 Highway Capacity Manual (HCM) will contain new capacity formulae for single-lane and two-lane roundabouts. The new formulae should be capable of providing accurate predictions of roundabout entry capacity, but concerns remain about whether analysts and designers will have all the tools necessary to develop roundabout designs capable of accommodating higher than expected traffic demand or differing driver behavior from one location to another. This article presents two alternative methods to adapt the current United Kingdom capacity analysis model for roundabouts to the design implications of using the HCM 2010 capacity procedure. The two adaptation methods are compared to show their correlation with recent U.S. practice, research and observations of built roundabouts. The first method equates the y-intercepts of current UK and HCM equations. The second method adapts the UK equation to the U.S. data by approximating the proposed HCM equation through a mathematical curve-fitting technique. Both methods have drawbacks. The first method does not improve the accuracy of the proposed 2010 HCM model, but the second method requires a more complicated adjustment technique. The ideal approach would be to continue to collect more data from saturated roundabout entries and to adjust the slope and intercept according to the UK calibration procedure.

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