Road transition zones between the rural and urban environment: evaluation of speed and traffic performace using micro-simulation approach.

A micro-simulation approach is presented for evaluating the effectiveness of a transition zone connecting the rural to the urban environment by using speeds computed in simulation for showing whether drivers slow down far enough below the imposed speed limit before entering the small urbanized area. The proposed approach was also applied to prove whether both within the transition zone as well as on the rural roads approaching this zone, acceptable values of the traffic performance measures expressed in terms of travel time, delay time, mean and maximum queue length, and stop time, were ensured. Five design alternatives based on the horizontal deflection obtained by means of engineering measures associated with different combinations of a T-type intersection and/or roundabouts were tested. The results showed that the simulated mean speeds were lower than the 50 km/h speed limit imposed at the start of the urbanized area for all transition zone schemes investigated. However, the scenario with a roundabout and a T-type intersection to which two auxiliary lanes for right-turns were added was also identified as having better values of the traffic performance measures both within the transition zone and on rural roads entering this zone. The transition zone that was built, in accordance with the experts’ judgments, was found to confirm the effectiveness of the simulated solution in the field both in reducing vehicle speeds and in ensuring acceptable conditions of traffic flow. The design alternative implemented in simulation with the two roundabouts (one of which with two by-pass lanes for right-turns) may represent a future reference for further improvement in the built transition zone. In fact on a roundabout as an alternative to a T-type intersection a reduction in the number of traffic conflicts due to vehicles trajectories is generally expected, and consequently even fewer crashes are also expected to occur at this intersection. Additionally, the present paper introduces also a speed-delay time model based on the results of micro-simulation analysis