Given that GPS gets confused and thinks you're on surface roads when you're on the highway and vice versa, I don't see how this will always work. In dense urban

Given that GPS gets confused and thinks you're on surface roads when you're on the highway and vice versa, I don't see how this will always work. In dense urban areas there are often multiple layers of roadways going the same direction with very different speed limits. Also basic issues like GPS errors because of tall buildings or foliage cover can easily confuse systems such that you look like you're 100's of feet away from your actual position.