Perfect Driving Song
This is clearly not a unique property of a song, unlike for example, the perfect pop song. It depends on whether you are alone, with a partner, or kids; the time of day (morning is NOT the same as evening; and heading home from work is not the same as a late night emergency run to WalMart [sic]); time of year; and location, location, location. Going through the 101-I-10-210 interchange in downtown LA is different from cruising from Urbana to O'Hare, is different from cresting Independence Pass, is different from threading the M25 junctions, is different from doing a night run on the Autobahn, is different from taking a "AWD only" shortcut over a mountain in Iceland...
Having said that, clearly the perfect car song is "Þrjú Hjól undir bílnum" as done by Ómar Ragnarsson. I am not being deliberately obscure or anything here, it just is the best car song ever done.
In the interest of outreach and fair use, I present Þrjú Hjól .... Get thee hence to tónlist.is and buy some now!
However, in the interest of global accessibility, I'll go with "If I should fall from grace with God" by the Pogues. It is best suited for LA driving, since KROQ can't be completely relied upon; but it will do almost anywhere.
In a different mood I'd take "All I wanna do" by Sheryl Crow will do; as will "Paradise by the Dashboard Light" by Meatloaf.
In a different place, I'd take "A13, Trunk Road to the Sea" by Billy Bragg, or "Alright" by Supergrass.
Anything by the Beach Boys can also do on some occasions; but "Men of Harlech" done by any good welsh choir (men's) will also go a long way on occasion.