Driver Behavior and Gap-Acceptance Characteristics at Roundabouts in California

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 at seven single-lane and three multilane roundabouts in California. Results indicate that the mean critical headway is consistent with the values recommended 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 major factors affecting critical headway and follow-up headway. Results from this study enhance the existing database related to drivers’ gap-acceptance behavior at U.S. roundabouts.