It can be dangerous to drive with objects strapped to the roof of your car — especially for the vehicle behind you. A 2012 study conducted by the Government Accountability Office found 51,000 crashes occur each year from cars that were struck by improperly secured objects flying off moving cars or that hit highway debris, resulting in 10,000 injuries and 440 deaths.

It’s not just large or heavy items that can wreak havoc. At 55 miles per hour, a 20-pound object that falls from a vehicle can strike with the impact of half a ton, according to the U.S. Department of Transportation.

Here are tips on when, why and how to safely strap things to the roof of your car or the bed of your truck.

Related: How to Winterize Your Car

First, the law

Unless your vehicle is part of a commercial fleet governed by the Federal Motor Carrier Safety Administration, there is no federal law requiring you to tie down loads to your vehicle. But 15 states have already passed laws to impose fines or other penalties for improperly secured loads, and many of those same states ramp up the penalties significantly — sometimes even including jail time — if flying debris from your car causes an accident.

If debris flies from your vehicle on the road, many states can also issue a summons for littering, which can result in hefty fines. The Washington State Department of Ecology estimates 12 million pounds of debris are strewn across the highway each year from improperly secured loads, which accounts for nearly 40 percent of littering tickets issued by their highway patrol each year.

Related: What to Do — and Not to Do — If You’re Stopped by the Police

How to tie down a load

Tie down just about anything that isn’t part of your vehicle’s body. That includes obvious loads like luggage on the roof, but also things like loose clutter or heavy appliances in the bed of a pickup truck. According to the National Highway Traffic Safety Administration (NHTSA), “just because an object in the back of a truck is heavy does not mean it can’t be ejected from a vehicle — even under everyday circumstances like hitting a pothole or braking sharply.”

Put a cap on it. If you own a pickup truck and routinely use the bed to cart things, one easy solution is to buy a cap for the truck bed. Also known as camper shells and toppers, this bed cover comes in a variety of styles and materials and will keep your stuff secure.

Tarp and strap. If you’re driving a car or SUV, the Washington State Patrol advises loading lighter items on the bottom with heavier items on top to help hold them in place. Next, cover your entire load with a tarp to prevent pieces from flying free. Secure the entire load to your car using tie down or ratchet straps, rope, netting or a chain.

If you’re carrying a large item, tie it directly to your vehicle. Allstate Insurance Company recommends using roof racks with a hard-shell rooftop carrier or cargo bag for luggage. For larger items, they advise using ratchet straps that are at least two inches wide. Use a minimum of two straps, and use more for longer items.

Avoid outliers. Nothing should extend past the rear or front bumper, and if you’re carting any bundled items like lumber, Allstate advises using cling film to tie them together.

Make sure you haven’t overloaded your vehicle. Know the weight that your car or pickup truck can safely haul. Check the owner’s manual if you’re not sure what the limit is.

Related: How to Make Your Next Car Safer

Like this article? Share it with friends by clicking the Facebook or Twitter button below. And don't forget to visit our Facebook page!

Paul Hope, a trained chef and DIY enthusiast, has restored two houses and writes about food and homes.