Regular longboards go much faster than an electric one like those described here. I recently built an electric skateboard using one of the ESCs in this post and

Regular longboards go much faster than an electric one like those described here. I recently built an electric skateboard using one of the ESCs in this post and on flat ground it can't go much over 20mph. It goes far faster than that on even a slight slope. Maintaining control at that speed is dependent on the trucks. The ESCs do have brakes. They make downhills easy to manage. The only problem is that, without some special components, the brakes don't function on a 100% full charge. (The brakes are regenerative, so the ESC watches the voltage and doesn't allow the motors to overcharge the batteries.) That's not a problem in 99% of cases -- it only matters if you start your trip on a large downhill. That said, anyone learning to ride an electric skateboard should learn how to bail. You'll have to do it eventually.