In theory there is separate oversight over public transit in the United States as well. In California the CPUC regulates, for example, Muni and BART while the CHP has oversight over agencies that use state and federal highways (the subset of the Muni fleet that runs down Van Ness and 19th Ave is under the purview of the CHP). In practice the regulators are feckless.

Not to nitpick. But JR is not really one company, even though you get the impression that it is, due to the homogenity of, for example signage, partially quite comparable rolling stock and a shared (extremely efficient) reservation system.

From Wikipedia: [1]

The Japan Railways Group, more commonly known as JR Group (JRグループ Jeiāru Gurūpu), consists of seven for-profit companies that took over most of the assets and operations of the government-owned Japanese National Railways on April 1, 1987. Most of the liability of the JNR was assumed by the JNR Settlement Corporation.

[1] https://en.wikipedia.org/wiki/Japan_Railways_Group