It's 3:08 a.m. and I can't sleep. Sure, it's the first time I've bunked in the back of a Tesla, propped up on a squeaky, unstable air mattress. And yes, it doesn't help that there's two of us crammed ...

When you're driving on land, speed is measured in either miles per hour (mph) or kilometers per hour (km/h). These measurements are straightforward because you can see stationary landmarks and ...