Robo legs (& Robo suits) are considered to assist carry weights in factory. for example, Honda's Robo Legs (http://www.wired.com/2008/11/honda-announces/)
Current research is going in the direction of weight, but not speed.
I foresee this being a new vehicle for transporting a person. This mechanism needs "zero" learning curve. User just need to walk, run. it shall automatically speed up. achieving 60-80 kmph should be possible easily.
Feedback mechanism in this could be reading the neuro signals (motoneuron) from brain to legs (similar to Cyberdyne Robo suit, HAL). or learning from the body angle and leg landing angles. a person's body angle is different when he is trying to speedup and when he is trying to stop. similarly leg landing angle.
A person with this type of vehicle will find himself walking on low gravity planet :) each jump takes him a long distance. Person won't be tired even when he is running @ 80 kmph.
Probably this will be first vehicle without wheels !! Because of this, it does not need a huge infrastructure.
I see some research going in the direction assisting disabled in climbing stairs and walking. eg:
Honda's walker : https://www.youtube.com/watch?v=pp4XUvgqkbU
http://newsntechpalace.blogspot.in/2009/08/robot-suit-to-help-disabled-walk-climb.html
Some of the other advantages I foresee with these:
1) a fat man will be advised to walk to put down weight. But because of his weight, his knee and ankle joints will be worn. This Robotic augmentation helps them not to.
2) As this vehicle does not use wheels, it does not need a huge infrastructure like roads (may be good flat surface needed at high speeds)
3) Fuel efficiency will be more due to payload/overhead ratio is better (person weight / vehicle weight)
4) compared to cars, this gives some physical activity too. hence user will be healthier.
5) Road foot print required for one vehicle is very less
Ref:
-> Robonaut: http://robonaut.jsc.nasa.gov/default.asp
-> X1, a robotic augmentation riff : http://techland.time.com/2012/10/15/meet-x1-the-exoskeletal-robot-suit-that-could-make-astronauts-super-strong/
-> Cyberdyne Robot Suit, HAL: http://www.robotcenter.co.uk/products/cyberdyne-robot-suit-hal