I don't know too much about vehicle side of things but my understanding is the following:
MISRA is not on the same level as DO-178. DO-178 covers a lot of ground, from testing, documentation, requirements, that sort of thing, and it's made by a government agency which enforces it during certification, where every single hardware and software component in the aircraft related to flight operations is certified individually. So you will actually have engineers from the FAA sit down and look at code coverage, how requirements are written, how they map to tests, see if the tests cover a lot of cases in your requirements, see if the code implements the requirements, that sort of thing.
MISRA on the other hand are treated like guidelines that car manufacturers generally want you to meet when you deliver them a vehicle component.
There is the Federal Motor Vehicle Safety Standards you have to meet on a vehicle as a whole, but I do not know if they have to prove that they meet the following during a formal certification process.
http://www.nhtsa.gov/cars/rules/import/FMVSS/
So as far as I know, there's big approval process at the end for vehicles, while there's a formal certification process for all components in an aircraft, as well as a big approval process at the end for aircraft.
Someone please correct and fill in the blanks for the vehicle side of things.
