I just drove from San Diego to Baltimore, almost 3,000 miles. Before leaving San Diego, I took my car to my trusted mechanics and asked them to check it over for a road trip. They took the wheels off and looked at the brake pads, and said that all four were between 8-12mm. I drove across the country, most of the time on cruise, not braking particularly hard or frequently, even when coming down off the mountains.
I took the car in to a shop upon arriving in Baltimore for a state-mandated inspection, about 2 weeks since the initial pre-road trip check. They said my front brake pads were at 2mm!!! I paid to have them replaced, of course. Unfortunately, I don't have the info handy to say when the pads were last replaced, but I think it was about 2-3 years ago.
My questions are: do brake pads wear down THAT quickly? Does long-distance driving wear them down excessively, despite infrequent braking? Is the most likely explanation that the pre-road trip assessment was way off?