Answer: Windows down. If you can't roll them down, break them. Ideally, every passenger can break her/his own window.
This one has always bugged me. Traffic fatalities in 2017: 40,100 Vehicle drowning deaths, the last time anyone estimated (2004-2007): 384 Percentage of traffic deaths that are drownings: 0.96% Percentage of vehicular drownings also involving a rollover: 63% Percentage of vehicular drownings also involving another vehicle: 12% So let's review: if you're in a fatality-grade accident, there's a less than 1% chance you're going to drown. If you're in that less than 1%, there's a better than 50% chance you're not wearing your seatbelt and 63% chance you've flipped the f'ing car. You are, in short, driving like a ragged asshole. Here's the thing: for a vehicular drowning to enter your future you have to have made some pretty dire mistakes. Chances are good you're not sitting there rationally. There's been a long list of bad decisions here and remembering five steps from Popular Mechanics probably isn't going to help you out much (especially if you've rolled your car without a seatbelt on, which statistically speaking, is exactly what you just did). Yet the mindspace of this particular dilemma is huge - there are more instances on that page than, statistically speaking, vehicular drownings in four months nationwide. That bridge in Mt. Vernon? Where the road suddenly was in the river? Nobody drowned.The most common scenario was a single vehicle leaving the roadway, colliding with a fixed object and then rolling over before ultimately becoming submerged. He further reported that in cases where restraint use was known, the victim was unrestrained more than half the time.
When motor vehicle submersion deaths caused by flooding are considered, the number of annual incidents grows by at least another 60 deaths. According to Flood Fatalities in the United States, “[f]loods are the second-deadliest U.S. weather-related hazard.” Northern Illinois University researchers compiled a comprehensive flood dataset for a 47 year period spanning 1959–2005, and found 4.586 flood fatalities in the contiguous U.S. They concluded that, “[f]or all flood types, a majority of fatalities occurred in vehicles (63%).”
Sure you have math and numbers and history and evidence and reasoning and common sense on your side, but I'm gonna have my damned life savin' hammer, no, my glock to protect me from some bridge built by some pointy-headed know-it-all that freaking collapses under me, probably 'cause some eeeleegal alien waz drivin' the semi that hit that wimpy bridge and my pickup truck and my six cases of Marlboro Reds that I'd picked up at the Piggly-wiggly. Sheeit!
I've heard that the pointy tips on the bottom of removable headrests are made with very hard points, designed to easily break windows in an emergency. Could be a false rumor though, I'll try and find a source link in a minute when I'm able. Edit: Apperently it wasn't a design intention but it is effective https://www.snopes.com/fact-check/car-headrests-emergency-escape/
They make a tool designed to easily break a window because there's apparently a market for tools sold to people with anxiety about being trapped in a submerged car https://www.amazon.com/dp/B00E8CV0EQ/ref=cm_sw_r_cp_api_i_qH2wCbBQW2R36