Butterfly away Henry Ford and automobiles remain rich people's toys in the US. So, as we move through the teens, twenties and early thirties, more effort goes into faster and improved railroads. Of course, UK and Germany won't be standing still, but without the American example, cars might spread a little slower. Given that cars were still not elements of long distance travel until mid-century, you might have a situation where the car boom coincides with the jet air travel boom.