Dynamic penalty function approach for ramp metering with equity constraints

This study proposes a non-linear programming optimization model that could simultaneously consider the ramp metering efficiency and equity issue. Equity indexes are defined to capture the degree of equity of the ramp metering, which are formulated as constraints in the model. Dynamic penalty method is adopted to deal with the constraints since they are soft in nature in which solutions with small violations could be acceptable. A modified cell transmission model (MCTM) is chosen to simulate the traffic flow propagation in the network where the objective function value is derived from it. The results of the case study show that the proposed methodology could give better solutions compared to initial solutions. However, the equity indexes obtained are low. It is anticipated that the results for equity indexes can be improved if the penalty coefficients could be fine tuned properly.