Stuck in your car in a snowstorm: stay inside, clear the exhaust, and what a Japanese CO test showed

Getting stuck in your car in a snowstorm is cold and frightening, but the bigger danger is invisible: carbon monoxide from an exhaust pipe buried in snow. U.S. and Japanese guidance agree on most things, and differ on one interesting point.

The U.S. advice (NWS and Ready.gov)

Ready.gov says to stay off roads if at all possible, and if you are trapped in your car, to stay inside. The National Weather Service (NWS) explains why: if you leave your vehicle, you will become disoriented quickly in wind-driven snow and cold. The NWS also advises:

• Run the motor about 10 minutes each hour for heat.
• While running the motor, open the window a little for fresh air to avoid carbon monoxide poisoning.
• Clear snow from the exhaust pipe.
• Be visible to rescuers: turn on the dome light at night when running the engine, tie a bright cloth (preferably red) to your antenna or door, and after snow stops falling, raise the hood to show you need help.

What a Japanese test showed

JAF, Japan's automobile federation, buried test cars in snow in Asahikawa, Hokkaido, in February 2015 and measured carbon monoxide inside with the engine running:

JAF says that exhaust can enter through gaps in the body even with recirculation on, that the most important step is to clear snow from around the exhaust regularly, and that you should turn the engine off as much as possible while you wait. It also cautions that results depend on wind, the car's surroundings and the air-conditioning setting.

So: opening a window helps but is not enough on its own. Clearing the exhaust, and running the engine as little as you can, matter most (our reading of both sources).

Before you drive in winter

• Ready.gov recommends a car kit with jumper cables, sand, a flashlight, warm clothes, blankets, bottled water and non-perishable snacks, and a full tank of gas; a full tank also keeps the fuel line from freezing.
• Japan's road authorities ask drivers to avoid going out when heavy snow is forecast and, if they must, to fit winter tires, carry chains and put them on early, and carry a shovel and sand.
• In Japan, roads under a "chain regulation" cannot be driven without tire chains, even on studless winter tires; spray-on traction products do not count (MLIT).
• Add a shovel small enough to dig out the exhaust, and a portable toilet (our suggestion).

Related: Hypothermia and frostbite, Never use stoves or heaters inside a tent. Our Japanese edition: 大雪で車が立ち往生したら.