A Segment-Based Railway Scheduling Model for Minimizing Waiting Time in Developing-Country Networks: Economic and Environmental Co-Benefits

In developing countries, railway networks often create operational bottlenecks by combining older single-track sections with modern, double-track, signaled infrastructure. This study addresses train scheduling in such hybrid networks using a segment-based rather than a train-based approach. A mixed integer linear programming (MILP) model is developed that minimizes total waiting time across all journey segments, incorporating directional safety intervals separating single-track and double-track sections and co-directional and counter-directional movements. Train-type priority is included in the objective function as a class-dependent, age-adjusted weight, rather than a rigid priority rule; thus preventing the unlimited delay that a rigid priority ranking might otherwise impose on lower-priority trains in heavily shared resources. Since an exact MILP solution is impractical on a national scale, a segment-based heuristic method is developed; the age-weighted heuristic method, validated against exact solutions on smaller subnetworks, is found to require 35% more time to reach full optimum. This approach, applied to Turkey’s national railway network (109 routes, 997 stations or siding sections, 2281 transit segment between two stations or siding sections, 1539 daily services), has reduced daily waiting times from 2508 h to 609 h. This corresponds to an annual saving of approximately $13.2 million in fuel and labor costs and a reduction of 24,260 tons/year in CO2 emissions. Since diesel-fueled services account for more than 99% of the cost savings, sensitivity analyses show that these estimates are robust against fuel price assumptions. The study offers a low-cost solution for improving railway capacity before costly infrastructure investments and is expected to be generalized to similar heterogeneous national networks.