Equity-based link capacity optimization model for multimodal transportation networks

With rapid urbanization and rising travel demand under limited construction resources, transportation network optimization must, beyond efficiency, account for fairness in the distribution of traveler benefits. Focusing on multimodal networks, this study develops an equity evaluation system covering benefit distribution, resource occupancy, and social cost sharing, and proposes a bilevel optimization model whose upper level minimizes the equity indicator. The upper level allocates link capacities using an improved elitist genetic algorithm, while the lower level represents travel choice via a Logit-based stochastic user equilibrium (SUE) that iterates with the upper level. The case study shows that when the OD demand between two points is 3000 and 2500, the model optimizes the multimodal transportation system under five schemes, with Scheme 4 significantly improving equity. The benefit distribution index is 0.999, the road-space Gini coefficient decreases to 0.452, the social cost burden index is 47.17, and the objective function is optimized to 4.539. Sensitivity analysis indicates that as the OD demand increases from 7500 to 115000, the effect of network optimization becomes more significant, and the marginal benefits gradually increase. The model proposed in this paper provides operable modeling and decision support for the coordinated optimization of equity and efficiency in multimodal transportation networks, with broad practical application prospects.