Capacity of Single-lane Roundabouts in Hungary

Roundabouts are a prevalent type of intersection known for their potential to enhance traffic flow. Ensuring their effective design is crucial for optimizing traffic performance. This study focuses on evaluating the capacity of roundabouts, essential for both planning new installations and assessing existing ones. Field data from thirteen roundabouts in Hungary were analyzed to estimate critical gap and follow-up headway values for each entry. Employing Raff's graphical method, critical gap values were determined, while follow-up headway was calculated by averaging the time taken for two waiting vehicles to accept the same gap over eight instances. The critical gaps and follow-up headway values for all forty-one entries ranged between 2.41–3.46 s and 1.8–2.4 s, respectively. Subsequently, the Highway Capacity Manual (HCM) roundabout capacity equation was calibrated using these gap acceptance parameters. The proposed model yielded higher entry capacity (1,672 PCU/h) compared to the HCM model. Validation against actual field entry capacity values demonstrated a strong correlation (R2 = 0.94), affirming the model's accuracy. Comparisons with international models, such as HCM 2016, Brilon-Wu, and Brilon-Bondzio, revealed the superiority of the proposed model in terms of entry capacity (1,672 PCU/h versus 1,380 PCU/h, 1,241 PCU/h and, 1,218 PCU/h respectively).