Rail carfloat services make economic sense only under a narrow set of circumstances, where there's no natural place for a direct overland rail link, the alternative route is very long, and the volume of traffic is too low to justify building a bridge but too high to make it practical to unload and truck the freight by road. San Francisco Bay and NY Harbor are two examples. Crossing NY Harbor from the mainland by freight rail, for example, involves a 250 mile detour upstate and back.