Arnott, Richard, and An Yan. “The Two-Mode Problem”. Boston College Working Papers in Economics 474, 2000.
Suppose that there are two congestible modes of travel from A to B - road and rail for concreteness - which are imperfect substitutes in demand. Road congestion from A to B is underpriced; this is an unalterable distortion. Compared to the first best, should the transportation planner choose a wider or narrower road, raise or lower the rail fare, and expand or contract rail capacity? This paper provides a synthetic review of the literature on the problem, presents some new results, and discusses directions for future research on this and related second-best problems.