(Last summer I rode my bicycle.)
Wedged my Garmin Etrex Vista with street maps between the windshield and the dashboard. Same exact GPS as the one I had on the handlebars of my bike while crossing the continental US in summer. Bike crossing from San Diego CA to Savannah GA took 17 days. In the car it was a tiring but comfortable 4.5 days (43 hours of driving time not including pit stop/meal times) from Tucson AZ to Boston MA for about the same number of miles (2800) and climbing (84000 ft). Basically, around 12 hours a day from motel to motel. Stats below:
Yes, it is cold in January! Fuel economy was good though. Almost 30.5 mpg. No speeding tickets. And averaging nearly 65 mph is a pretty sensible average for a multiday drive.
(My friend Jim shadowed me in his Dodge Grand Caravan the whole way. I wonder what mileage he got.) The Etrex switches to night mode automatically as it gets to dusk. Some of the driving ended up after dark (up to 9pm one day). Never saw it switch on the bike, on the PacTour Elite Transcontinental, the daily miles always finished before dark.
Cost of this trip is around $800 for gas and hotel. Cost of the bike trip was $3000.