I've gotta system I employ from time to time. @ 70-75mph if I can't see your parking lights in my review mirror we're probably going to have problems. If, at those speeds, I can not see the front of your hood - yep... we're slowing down. If it get's to where I can not see your windshield wipers in my rearview mirror... You ain't gonna be a happy camper at all. All of that said with the understanding that short of tailgating the vehicle in front of me or the fact that I'm in the slowest lane provided, short of the break-down lane - I'm going fast as I can.