Mature deer run at 30-35mph and weigh 90-200+ pounds depending on sex and where you are in the US. They are tough to kill or injure. Two have run into the side of my car and I have had to stop quicky many times in my car and also on my bike..... I can see hundreds on an early evening ride and have had many close calls but fortunately have not hit one. I keep my eyes peeled and will make some noises if I see them locked up on the side of a field because they can spook at the last second and jump out into you. Fawns especially dumb and this is the worst time of the year because they don't have the fear of humans as much as they will in a month or two. Bucks are usually much more nocturnal and you won't see as many on sunset type rides. I just shout "Hey" and they are usually gone.