I don't understand where you are trying to go with this - steam cars have the same primary feature as any other vehicle - longitudinal and lateral control to traverse asphalt bands across the country. They can be retrofitted with any modern convenience feature as that stuff does not need to be integrated into the propulsion system. The same can be said of any other vehicle made between then and now. Of course, nobody has retrofit an early 1900s vehicle with 12 impact sensors and multistage airbags, and no modern manufacturer has offered a steam powerplant, because nobody actually wants this. Products are sold on features, not principles. In the US, you can (and people do) build just about anything and drive it legally on the road, so if not a single person has created (whatever it is several people in this thread think should exist), it would be preposterous to think a manufacturer would do it.