The United States is a very large place so driving cultures can be surprisingly, even hilariously diverse. Regional driving aptitude and situational awareness can range from commendable to terrifying, so stay on your toes when venturing into unfamiliar territory.
Knowing the local driving laws and unspoken road rules are just as vital when undertaking a road trip. What's the speed limit on unposted roads? If someone flashes their high beams is it because your high beams are on and you're blinding oncoming traffic, or because there's a cop hiding around the next corner with a speed detector? If you give someone the finger, will you receive the finger in return or will gun-play ensue?
Old school rules
The first speed limit law in the US was set in Boston in 1757. On Sundays, wagons, carriages and horses could not exceed walking pace. The fine: 10 shillings. Contemporary speed laws are sometimes a little more arbitrary. California's 'Basic Speed Law' and New York's 'Reasonable and Prudent' speed law can theoretically get a driver fined no matter the posted speed limit, if you don't stick with the flow of traffic or are otherwise deemed to be a nuisance.
Though rarely if ever enforced, there are aging, peculiar laws all over the country that confound reason, but are nevertheless still on the books. In New Jersey and Ohio, legally one must honk their horn whenever passing another car. You can be ticketed if you leave your traffic-side car door open longer than is deemed necessary in Oregon. And ladies, driving while wearing your housecoat is illegal in the state of California.
New rules to keep in mind
Generally speaking, texting while driving is merely a sign of dangerously low IQ, but since common sense isn't necessarily a prerequisite for getting a driver's licence, 39 states have taken the extra step to ban drivers from text messaging. Likewise, 10 states have also banned hand-held mobile phone use and drivers can be cited without any other traffic offence taking place.
While strapping a dog to the roof of a car is technically only illegal in Massachusetts and Alaska, it's frowned upon pretty much everywhere else too. It's legal for women to be topless in New York, except for Sag Harbor where it's illegal to disrobe in one's car.
Though we're certain a fascinating tale accompanies this regulation, Alabama law books state without further elaboration that it's illegal to drive while blindfolded. Likewise, we're on the edge of our seats to hear the gripping drama that led Glendale, Arizona, to ban driving in reverse.
The unspoken rules
US folklore says that if you're stopped at a red light and the driver next to you looks over and nods meaningfully, this means they want to drag race – though this may only be true if you're in a low-budget movie shot in the 1960s. If it happens today, it's more likely they're just creepy and you should slap the power locks immediately.
Though it would cause an instant 10-car pile-up if done anywhere else in the world, a sizable group of drivers in the US think it's OK to communicate that one is driving too close to their bumper by briefly hitting the brakes. Usually these people are camped out in the left lane – traditionally the passing lane – and have elected themselves speed vigilantes. If you don't have a bazooka with you, then it's probably a good idea to just give them plenty of room, because who knows what other brainless/dangerous manoeuvres they're going to pull?
Finally, and sadly, Americans are famously oblivious and/or dismissive of other drivers. This is particularly true at filling stations, where not only do people dawdle at the pump, they behave as if they've just pulled into their private garage. Even with 12 cars waiting, people will indulgently wash their windows, check the oil, answer a text message, then meander inside to pay, spending five minutes choosing snacks. If people are waiting, fill the tank, then promptly pull out of the way. Nothing ruins a road trip like a hair-trigger, road-rage guy dispensing tire iron justice on your brake lights.
Leif Pettersen is a Lonely Planet author, freelance travel writer and polyglot. He’s visited 48 countries (so far) and can be found @leifpettersen. He's also American, so he's allowed to say these things.
This article was originally published in June 2012. This article was updated in October 2012.