Car Talk Algebra Puzzler

I came across a math puzzle from Click & Clack on NPR's always entertaining Car Talk, see if you can figure it out, it goes like this:

"RAY: Last month, Tommy and I decided that we were going to take a trip north to see the foliage. Tommy drove the first 40 miles. I drove the rest of the way. We looked at the foliage for three or four minutes, then decided to head home.

We took the same route home.

On the way back, Tommy drove the first leg of the trip and I drove the last 50 miles.

I got home and my wife said, "Who did the driving?"

I explained that Tommy drove the first 40 miles, then I drove the rest of the way. On the way back, Tommy drove the first leg of the trip, and I drove the last 50 miles.

She said, "But who did most of the driving?"

I told her, "You can figure it out. In fact, you can even figure out how much more of the driving was done by that person."

And that's the question. Who drove the most -- and how many more miles did that person drive?"