I found this post on a talkdisney forum.
My Mom sometimes drives over to the parks to meet me (when I'm staying on property). I use WDW transport exclusively One afternoon we were going from AK to MGM and she said "Why don't you just ride with me it'll be quicker" I refused. I waited 10 minutes at least for a bus and I steal beat har to the park by about 5 minutes.
Most people don't factor in waiting for trams, walking to the car, and driving the long about way (WDW bus drivers know all the shortcuts and dont have to wait for parking tolls etc.).
Not saying WDW transport will Always beat your own car, but it probably will alot of times, plus its fun, and easy! (And hey your saving money on gas too!!!)