Computer-aided analysis and evaluation on ramp spacing along urban expressways

High traffic efficiency on urban expressways and their ramps is the crucial requirement to ensure the optimum design and reliable operation of urban traffic networks in large cities. The mismatch between ramp configurations and spacing can lead to the dramatic drop of traffic capacity and efficiency. The traffic performance in different scenarios for four typical configurations along urban expressways is simulated after the calibration of simulation model. The results are then evaluated through the data envelopment analysis (DEA) and analytic hierarchy process (AHP). The traffic simulation software VISSIM is employed to calculate the critical variables and parameters able to represent traffic performance of urban expressways and their ramps in terms of traffic practice. To carry preferable multi-criteria evaluations from simulation process, the DEA and AHP method are used together to find the appropriate spacing between ramps and evaluate the effects from the different design speeds of frontage roads and opening time of ramps. The proposed method also gives the ranking of different scenarios for four configurations. The applicability and effectiveness of the proposed evaluation methods are demonstrated in case studies where some critical parameters for traffic designs and operations about ramps are practically given through field survey. The results show that the proposed methodology is vitally important for traffic planners and designers to assure an effective evaluation and decision support on complex transportation systems.