Critical headway and follow-up headway are two important parameters to perform design and operational analyses at a roundabout. This paper addresses drivers' gap-acceptance behavior characteristics at roundabouts and presents the results of critical headway and follow-up headway measurements atseven single-lane and three multi-lane roundabouts in California. The results indicate that the mean critical headway is consistent with the valuesrecommended by the newly completed research NCHRP 3-65; however, the follow-up headway is significantly lower than that recommended by NCHRP 3-65. This paper also reveals that circulating flow rate and speed are two majorfactors affecting critical headway and follow-up headway. The results from this study enhance the existing database related to drivers' gap-acceptance behavior at U.S. roundabouts.
Samenvatting