Operations research can be linked with the optimization of investment among different projects, including transportation. Moreover, it can also be utilized for managing resources on transportation construction projects. In addition, public transportation does benefit a great deal from operational research aspects for optimization of its operational parameters, including routes, fares, stations, number of vehicles. The same could be said for delivery or supply chain fields.
I think this question could have a wide range of answers. But as a case study, you can consider the following:
Equitable access to education: In many areas, the lack of a proper transportation system prevents students from getting an education. OR models can identify the best solutions for transporting underprivileged students.