ROUNDABOUTS - Comments on the SIDRA INTERSECTION Model and the TRL (UK) Linear Regression Model

There has been some controversy in relation to the lane-based gap-acceptance model used in SIDRA INTERSECTION software vs the approach-based linear regression (UK TRL "empirical") model used in RODEL and ARCADY software for estimating the capacity of roundabouts. This is relevant to the US scene where roundabouts are relatively new. This detailed discussion note presents Dr Akçelik's views on the subject. A section on lessons learned from the US research on roundabouts leading to the HCM 2010 roundabout capacity model is included, and reference is made to the HCM 2010 model implemented in SIDRA INTERSECTION where relevant.