I have to keep my feet under me for a few dozen steps while I come to a stop. I might not be able to do that at 20 MPH, but I think I can at 12 MPH. I can at whatever speeds I was going when people ran over my back wheel. (Once was a parking lot, so I was probably going fairly slowly, but the other was biking downhill.)
Go to the gym, turn the treadmill up to full speed and jump onto it, and see how it goes. That'll be a good data based test. The mill will drop speed by about 30% and most mills don't go up super high. Take a face plant for science.
If you did then you're probbably faster than normal and better balance than normal. I'm pretty sure I'd pull a hammy immediately. My coworker immediately face planted and broke arm and collar bone.
This gets more true the further you are from sprinting on a regular basis. And really unless you have practice you're not going to match speeds with the ground anyway