One common thing I've seen is that he "accidentally" got on the highway somehow, so he didn't realize it was closed, and then because protesters were hidden behind a turn he "didn't see them in time."
Except A) There was plenty of time to see the protesers AND the cars blocking them
B) It doesn't matter, since if you look at the video you can see he's riding on the side of the road, for quite a while, in order to avoid the barricade. aka he obviously saw and had time to react, and decided "I'm going to just keep driving instead of slowing down."