Ah yes, MAP-21. It passed a requirement that all electronic toll systems become interoperable by 2016, but without any penalty for failure or money inducements

Ah yes, MAP-21. It passed a requirement that all electronic toll systems become interoperable by 2016, but without any penalty for failure or money inducements to succeed, so nothing happened. Well, that's not quite true. There are a couple of major consortia of electronic toll systems in the US. The largest consortium is the E-ZPass system, which started out with a cooperation in the NYC area and grew to encompass basically everything from Illinois to Virginia to Maine by the time MAP-21 passed. Since it was the largest, in terms of number of systems implemented, their position was more or less that everyone would implement compatibility with E-ZPass. North Carolina, Minnesota, Florida (and I believe Kentucky) added compatibility to E-ZPass post-2012. The other three consortia are California (interoperable with no one else, because California I guess), the Texas/Oklahoma/Kansas group, and the Georgia/North Carolina/Florida interoperability region (which will be fully subsumed by E-ZPass once Georgia's system becomes interoperable, apparently later this year). There's still a couple of systems that interoperate with nobody else as well.