Most people's initial reaction is they hate road walking. It's also their final reaction. Whenever I traveled in the Air Force, I always enjoyed walking around the cities we visited and that's how I got hooked. I gave up most driving in Oct 2011 and now I only drive about 3,000 miles a year. Most of it to go backpacking. Now that I'm walking, my city seems smaller.
Traffic isn't as bad as people think it is except in some places where it is worse. It's now possible to preview routes using Google Street view.
If I fastened the trailer to a bicycle, I'd still be in the same traffic with less ability to get off the road quickly.
Anyway, I live in Pueblo, CO. The Transamerica bicycle trail passes through here and the American Discovery Trail does also. Since it's on Route 50, it's on a natural route many people take across the country. I often meet them in my wanderings, and I guess I've caught the bug. Maybe I can't go across the country, but I can do what I can.
I put it in the off-topic section because roadwalking is significantly different than backpacking or hiking. The gear is almost entirely different. People are more individual in what they wear and many things work. The part of the equation most people miss on long road trips is having a cart. Of course, having a cart, you can't mix trails and roads like on the American Discovery Trail. But I've noticed most people stop following the ADT in the first couple of states.
If one looks at history, backpacking is a subset of road walking which didn't be come popular until about 1923 when the first national forest trails started to be developed. Even then, it was mostly car camping and short hikes. It wasn't until the development of lighterweight gear and hippies that longer hikes became popular. Sure, there were people who took long backpacking trips before, but they were the exception.
Backpacking is somewhat of an escape from society. Roadwalkers see society from a different point of view.