Did you know that low tire pressure, much like high blood pressure, can be unhealthy for your car? In fact, an estimated 11,000 tire-related crashes cause nearly 200 deaths each year according to the National Highway Transportation Safety Administration (NHTSA), which credits underinflated tires and overloaded vehicles as a major cause of tire failure.

In April 2015 a driver in Bristol, Connecticut was charged with negligent homicide after allegedly striking a pedestrian on a snowy street, having lost control of a car with underinflated and bald tires. According to a local news report, three of the tires were inflated between 21 and 24 pounds per square inch (psi), though the recommended psi for the driver’s car was 32.

Significantly underinflated tires are dangerous because they can overheat, says Dan Zielinski, RMA's senior vice president for public affairs. “Heat is the enemy of a tire. When tires are underinflated, heat builds up in the tire that can cause damage that may lead to tread separation. When that occurs, loss of vehicle control may occur.”

Related: Road Trip Checklist for Your Car

How to check your tire pressure

If you don’t know how to check your tire pressure — or you don’t know what the pressure should be — you’re far from alone. Just 17 percent of drivers know the right way to check tire pressure and half don't know where to find their recommended pressure level according to a survey by the Rubber Manufacturers Association (RMA), which represents tire manufacturers.

You should check your tire pressure once per month. They will naturally deflate over time, as well as after encountering potholes or striking curbs or when the weather turns cool. They lose 1 to 2 pounds of pressure for every 10-degree temperature drop, according to the Utah Safety Council.

Related: How to Change a Flat Tire

To check and adjust your tire pressure:

1. Buy a tire pressure gauge. Don't rely on the gauges attached to gas station air pumps. “Gas station inflation systems take a good deal of abuse, which can affect the accuracy,” says Zielinski.

Small, portable gauges are sold at auto parts stores and many general-merchandise retailers. They and cost anywhere from $5 to $50, but a good one can be had for under $15, according to Consumer Reports.

2. Let your tires cool down. Wait until your vehicle has been sitting still for at least three hours. Your tires have to be “cold” in order for you to get an accurate reading. If a tire has been recently driven, the air inside will have warmed up and expanded, temporarily increasing the pressure.

3. Get the numbers. Look for your vehicle's recommended tire pressure in the owner's manual. You can also find it on the driver-side door, glove compartment or trunk lid. The number will be next to “psi.” (It will also be listed metrically as “kPa, or kilopascals, for drivers who use the metric system.)

Don't use the “psi” number listed on the tire's sidewall. That’s the maximum — not the recommended — pressure, according to Zielinski. You want to avoid overinflating your tires. “Overinflated tires have a smaller contact patch with the road, which affects handling,” he says. “They also will wear out the center of the tread faster and will be more susceptible to road hazard damage.”

4. Check the pressure. On each tire, including the spare, unscrew the valve cap from the stem, located on the side of the tire. Fit the tire gauge into the stem. If you hear a hissing sound, which is air escaping, adjust the fit until it stops. Then read the pressure number on the gauge.

5. Adjust the pressure. If the number on the gauge is lower than recommended, drive to a nearby service station and add enough air to bring it up to the recommended number — but no higher. Don't try to compensate for warm tires by overinflating, which creates a safety hazard. Instead, perform a second check later, after the tires are cold again. Then return to add more air if needed.

If the number on the gauge is too high, just press the valve stem gently — you can use the side of the gauge for this — to let some air out.

On-board sensors

Starting with the model year 2008, all cars, trucks and light vans are required to have a Tire Pressure Monitoring System (TPMS). Using sensors, it automatically detects when a tire is significantly below recommended pressure. Then it notifies the driver by lighting up an indicator on the dashboard, which can look like one of two designs.

The sensors won't know whether the tire just needs some more air or has a potentially dangerous leak that could cause a flat, so the Tire Industry Association recommends having your tires checked by an industry professional whenever the indicator light turns on.

Even if your vehicle has TPMS, you should continue to monitor your pressure using a tire gauge. “[TPMS] only provides a warning when tire pressure drops 25 percent, which is a significant loss of pressure,” says Zielinski.

Related: Are Your All-Season Tires Really Good Enough for Winter?

David Arv Bragi is a freelance journalist and marketing consultant. He has been writing about health and safety issues since the 1990s and currently lives in Portland, Oregon.