I think it’s a simple post hoc fallacy. Stop signs proliferated afterBig Oil gained a degree of power over Congress, therefore Big Oil must be part of the cause.

That said, there is precedent for traffic laws being set by fuel consumption concerns and there was industry pushback against it that led to its repeal. https://en.wikipedia.org/wiki/National_Maximum_Speed_Law

The difference between Drive 55 and the stop signs is that Drive 55 was enacted by a single legislative act, and stop signs proliferate due to a combination of state code, municipal code, civil engineering practices and limited imagination. Traffic circles are currently proliferating just as easy, and reduce fuel consumption.