The secret to a long life is improving the odds.

If you wear a seat belt, for example, you've astronomically improved your odds of surviving a car crash.

To up the odds even more, we've put together a list of five "gotta-have" safety features to look for when shopping for a new or used car or truck.

If you're buying new, don't leave the showroom without them, even if you have to pay extra. If you're buying used, lean toward a car or truck with as many as possible.

First Gotta-Have: Side-impact air bags

Modern car design incorporates impact-absorbing crumple zones into the front end of vehicles to protect the cabin. But there isn't enough space in the doors to allow for crumple zones.

That's why side-impact collisions can be so deadly. Your head and chest will fare much better if they're cushioned from all the bent metal, shattered plastic and broken glass coming your way.

These bags are now available on most models, and they're increasingly available as standard equipment. If they're still an option, this protection can cost anywhere between $250 and $650 a la carte, or as much as $1,300 if the bags must be bought as part of an option package.

Second Gotta-Have: Anti-lock Braking System

Anti-lock brakes keep you from skidding and allow you to steer around all sorts of potential hazards, even with your foot jammed down on the pedal.

Slam on the brakes without ABS and you'll lockup the wheels, causing the car to skid or even spin. Anti-lock brakes repeatedly take your wheels to the threshold of locking up and then release them for an instant, allowing you to maintain control.

ABS is standard equipment on most new cars and trucks. Expect to pay $250 to $300 if it's not.

Third Gotta-Have: Brake Assist

Even with anti-lock brakes, studies show drivers have a tendency not to brake hard enough during emergency stops.

So a decade ago, Mercedes-Benz developed a system that can detect panic braking, and automatically apply full pressure, when the driver fails to do so.

Brake assist can reduce emergency stopping distances by 20% to 45% -- or as much as 70 feet -- which is easily the difference between a close call and a rear-end collision.

It's now built into most -- but not all -- anti-lock brake systems. Ask before you buy and consider a car or truck with brake assist to be much safer than one without it.

Fourth Gotta-Have: Electronic Stability Control

Stability control helps your car stay on its intended course by sensing tire slip before you do and taking immediate corrective action -- automatically applying the brakes and cutting back on the throttle -- to avoid a skid and keep you in control.

Think of ESC as an unseen hand keeping your vehicle on the road. It's an absolute must on sport utility vehicles, which are particularly prone to tip and roll over if they skid.

Indeed, the government says stability control must be on all new cars and trucks by 2012, and will prevent up to 9,600 deaths and 238,000 injuries a year once every vehicle has it.

Look for ESC to become standard equipment on an increasing number of models between now and then. If you've got to spend extra for it, you may get away for as little as $200, but don't be shocked if ESC is bundled with other options that pushes the price above $2,000.

Fifth Gotta-Have: In-Car Telematics

Whether they're called OnStar, Tele Aid or Lexus Link, these wireless systems connect your vehicle to a 24/7 command center that knows where you are and can communicate with you and your car.

Benefits range from mundane -- directions to a restaurant or opening the doors if you're locked out -- to lifesaving -- automatically dispatching an ambulance anytime the air bags deploy.

The subscription price for telematic peace of mind should run $200 to $300 a year -- plus any activation fees and airtime charges -- depending on what level of service you subscribe to and how often you use it.

If you're buying used be aware that many systems built before 2006 depend on analog cell phone service, which will be discontinued at the end of the year. An upgrade to digital service can cost as much as $824 -- what Mercedes is charging to fix its Tele Aid hardware.

By Richard Homan

Interest.com Contributing Editor