I moved from the US to The Netherlands four years ago and traded in my 30 minute commute on the highway for a 7 seven minute commute on a bike and it has proven to be the best part about the move. It took some time to adjust to not wearing a helmet (you do tend to stick out if you ride around with one on.) The biggest issue in terms of safety is not the helmet but having dedicated, physically separate bicycle lanes. I mean *real* bicycle lanes, not just lines painted on the road. It feels like here that they plan the bicycle lanes first and then try to fit in the car lane in what is left over. It the US it always seemed that there was never enough room to add a proper bicycle lane because no one was thinking about that when the road was planned.

Hydrogen peroxide powered rocket packs fly for around 30 seconds, because they have a specific impulse of around 125, meaning that one pound of propellant can make 125 pound-seconds of thrust, meaning that it takes about two pounds of propellant for every second you are in the air. Mass ratios are low for anything strapped to a human, so the exponential nature of the rocket equation can be safely ignored.

A pretty hot (both literally and figuratively) bipropellant rocket could manage about twice the specific impulse, and you could carry somewhat heavier tanks, but two minutes of flight on a rocket pack is probably about the upper limit with conventional propellants.

However, an actual jet pack that used atmospheric oxygen could have an Isp ten times higher, allowing theoretical flights of fifteen minutes or so. Here, it really is a matter of technical development, since jet engines have thrust to weight ratios too low to make it practical. There is movement on this technical front, but it will still take a while.

John Carmack