by the time you're crazy enough to step out in front of any sort of semi in hopes it will stop, so you can rob it, i don't think you're doing risk calculations in a rational way.
Okay so put a mannequin with enough of a heater inside of it to pass for human on IR and strap it atop a roomba and then have THAT "step out" in front of a truck. It's a $1000 dummy and as long as you rob every 5th truck successfully (20%, but really you'll probably get 90% of them) you can make back all the money on busted dummies and more.