Ultimately, using the average of your GPS traces will be the best thing to do, although you'll need to drive a road at least a dozen times for them to average out enough to eliminate outliers. I would match them to the satellite map for now and use the GPS data to line it up later, if you're getting big tracking problems.
I've noticed a bunch of straight bridges aren't straight in the satellite pictures. I guess the angle of the satellite photo caused them to look curved! In this
case it seems that I'm lucky to live in a city with about a 10 foot range of elevations