[HNJohnC]

The reason is that human size and shape allows for replacing a human in any situation such as driving a vehicle or fitting into airline seats or what have you.

[finnw]

A robot that drives a vehicle can be an integral part of that vehicle, likely far cheaper than a humanoid robot that fits in the seat (and also shares the human driver's disadvantage of poor peripheral vision.)

[Goronmon]

Then how about being able to be a passenger in a vehicle with any special modification?

[mturmon]

Exactly. Entering a vehicle was one of the challenges in the most recent DARPA evaluation of teams developing high level control software for this robot.

[cookingrobot]

You could just use a pickup truck.