SCSC2003 Abstract S4260
TNCC and the No-Queue-Maximum-Throughput Indicator at Toll Facilities
TNCC and the No-Queue-Maximum-Throughput Indicator at Toll Facilities
Submitting Author: Dr. Marguerite Zarrillo
Abstract:
Toll Network Capacity Calculator, TNCC, is a queuing model for vehicles utilizing toll collection facilities with mixed lane configurations, lanes providing more than one type of toll collection service. It has been developed to determine a plaza’s maximum throughput such that there are no queues in any one of its many lanes, no-queue-maximum-throughput, NQMT. TNCC divides the arriving traffic into four categories and begins it computation with large arrival volumes such that queuing occurs at the plaza. TNCC then reduces this value using a computational iteration process until queues no longer exist in the plaza. It does this while keeping the ratio of arrival vehicles in the different traffic categories constant. Vehicles are also redistributed before the beginning of each iterative calculation according to some basic driver behavior assumptions. For instance, the TNCC model assumes drivers choose the lane that provides their required service but also has the smallest numb
er of vehicles in the queue. The model also assumes ETC vehicles choose dedicated lanes over mixed lanes.
Throughput was determined from plaza characteristics such as lane number, lane type and processing rates acquired in the field. The results of the calculations met constraints set by the characteristics of the arriving traffic. For instance, variables such as the percentage of arrivals that were patrons utilizing the electronic toll collection, ETC, service and the percentage of arrivals that were semi-trucks requiring non-ETC services influenced the plazas' throughput outcome. Functions describing the processing rates for ETC vehicles in the mixed lanes were also developed. Videotapes and transaction data at real plazas provided necessary input to in the application of TNCC to a toll plaza in Orange County, Florida. The maximum numbers of vehicles that can pass through several real plazas, without queue formation, were computed using TNCC.
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