The more I am seeing examples, and looking at the terrain, it seems like the problem is that it is only acting on the endpoints, and assuming that the map should simply extend from starting point to ending point, regardless of what is between them. But in the truth, it is quite possible to have an endpoint that cannot be accessed in a straight line because you must circle around a mountain, etc. These maps would need to account for those scenarios.
Yeah, I've seen some strange results as well, such as a large chunk of accessible area jutting through Olympia to Lacey from my starting point in West Seattle where the intervening land is not touched. I don't see how I could get there in 1 hour because the highways all go around the military bases and backwoods there.
There's a similar blob going from Seattle to Preston, which appears to contain some impossible routes where you would get off I-90 and then circle around via highway.
As long as you stay out of the mountains and don't cross any water it seems pretty accurate as a first approximation.
