If you're on a 45mph road and someone puts themselves in your path 10 feet ahead, no, we don't say that you should have actually been going 5mph just in case something like this was going to happen. You're required to yield at crosswalks, but there's an expectation that mutual acknowledgement between you and the pedestrian happens at a reasonable distance before the pedestrian enters the roadway. Similarly, if someone enters an intersection on red, you have a duty to try and avoid the crash, but if it's too late, that's on them.