Ex-ante evaluations for ramp metering facilities

Understanding the benefit of ramp metering facilities before they are built is an important task in the planning process. Hence, we propose a simple ex-ante evaluation that requires only a limited amount of data. Designed to be used by road authorities to check and justify the necessity of new ramp metering facilities, the proposed ex-ante (lat. for "before the event") method uses traffic flow and traffic velocity data for estimating the benefit of a ramp metering facility. The method compares the travel times at the intersection with and without controlling the traffic flows by a ramp metering system. The queuing time, which varies according to the volume of the traffic stream, is computed with the help of suitable queuing models and is considered in the calculation of the travel time. The potential of the facility is then calculated by the difference of the travel times with and without control at the intersection. The proposed method was developed on behalf of the German Highway Research Institute (BASt).