Only a little off topic: For a variety of reasons buses have not been able to take advantage of freeways which provide grade separated no cross street traffic and within 25 (even 5 miles) miles of a huge percent of the population. The Everett/Seattle to Portland/Eugene buses either drive/detour to several major and minor towns on the way adding upwards of an hour per stop, or they don't have enough passengers to make it a nonstop. Mostly such buses don't even exist. Astounding. The freeway system should have surface streets/freeway interchanges for passengers to board buses and vans. Uber/Lyft sorts of software should connect the best times for passengers to travel those 150 mile trips with the efficient use of vans and buses. Uber would even take me to the surface side of the passenger interchange.
To make this a little clearer. A passenger might tell the Uber/Lyft system they need to be in downtown Salem Oregon by noon next Thursday, and they are starting in North Seattle. The system would tell them they needed to be at the North Gate Interchange (about 100th St N) at 8:30 am. Also It could pick them up at their house at 7:50 am and provide a guaranteed connection. Or they may say the passenger would have to leave their house at 6 am. In any event a definite offer, and a seamless connection
The simple reason: people don't like buses. Look no further than Japan, the Expressway system has the equivalent of intercity bus rapid transit run by JR along all major freeways in the country, and yet people still choose the more expensive train (shinkansen or Limited Express). Why?
It's certainly faster, it's far more convenient, it's cheaper to operate (4-5 operators (1 driver, 2 conductors, 1-2 guards) for a 16 car train that carries 1300 seated passengers and can carry another 300+ more standees, it runs on electricity (which is always going to be cheaper), there are no tolls that JR is accountable for (Tolls are a huge expense in Japan), property income, etc), it's far more comfortable (there is no comparison here), among so many other things. However, this is Japan we're talking about, and despite Hokkaido, for the most part, not really adhering to these standards, the benefits of rail will almost always beat the plane, bus, or car for most intercity trips in the country.
The US only has about 4-6 corridors that are actually suitable for high-speed rail in the long term (San Diego to Vancouver, NEC (Portland to Norfolk), Toronto-Chicago (Maybe only Detroit-Chicago), Texas (Dallas to Houston), and Florida (Jacksonville-Miami (+ Tampa)). In the grand scheme of things, this doesn't account for the vast majority of trips throughout the country, but it certainly helps reduce the need for a lot of trips. Ultimately, people are moving back into cities so this may help things out longterm. Interstate bus service could become a reality in some areas that have high enough ridership to justify it (but low enough trip times that people aren't discouraged from using it), but I can't see it becoming the new reality, especially since Greyhound, Megabus, and all the other bus companies continue to cut bus services everywhere.
The freeways are also not in the most convenient of places for people. I live in Southern Ontario, and our intercity bus network is actually alright. We have short distance (30-200km) services run by a government body which serve most of the GTHA (but not Hamilton-Kitchener for some ungodly reason). Buses have their own lanes on a lot of freeways, and the toll road is a dedicated corridor for buses. However, stops are a pain in the ass and add so much time to the trip, plus, they require a lot of infrastructure to even be slightly convenient (bus storage, terminals, specialized on-ramps, parking, etc). Adding this infrastructure to the freeways won't be cheap in any way, and the fact that most living centres are away from freeways would be a disadvantage to potential users. Michigan might be a state where it could work (they have business loops in most cities along I69, I94, I96, I75, making reentry to the freeway slightly convenient), but they have a fairly robust Amtrak network that pretty much parallels all the freeways, plus it's faster so I don't see buses being big there any time soon.