How Side Curtain Airbags Work

Though traditional airbags were a significant development, they were most effective in straightforward crashes. In a front-end collision, for example, the engine compartment is designed to collapse and absorb most of the impact. A car that is hit in the side, however, has only the door and a few inches of space to protect the occupant. Drivers and front seat passengers were left vulnerable to side impacts; rear passengers were an afterthought.

Rather than reinvent the wheel, automakers studied crash test data to figure out where additional airbags would be most beneficial. Side collisions are most dangerous to a vehicle's occupants because the crumple zone is so small, so airbags were added to doors and front seats to protect the chest and thorax area of front passengers.

An early device was the head airbag, or Inflatable Tubular Structure, commonly found in many vehicles after 1998. When the car senses a side impact, the tube emerges and inflates, forming a firm 5 inch (12 centimeter) barrier across the front and rear windows. This tube prevents occupants' heads from being smacked into hard surfaces; however, it offers no protection from injury caused by limb movement or flying debris.

So, along came the advent of side curtain airbags, which "unroll" in a collision to provide protection to passengers in a side impact collision. Curtain airbags are most often mounted within the headliner above the doors and windows. As with traditional airbags, when the sensor detects an impact, some deploy through the material, and others are stored in a compartment beneath a panel that blows out.

Two convertibles introduced a variation on the technology, demonstrating the side curtain airbag's versatility. Porsche and Volvo both claim to be the first manufacturers to incorporate door-mounted side curtain airbags [sources: Mello, Wardlaw]. The airbags incorporate vertical air chambers (somewhat resembling an air mattress) that have a stiff structure, allowing them to deploy upward to cover the window area. Because these airbags are not based in the roof, they offer protection from side collisions even when the convertible top is down.

Though the technology is similar to other types of airbags, side curtains offer extra protection that traditional airbags might not, which we'll discuss in the next section.

We've already talked about how side curtain airbags were first developed to provide head and neck protection to passengers in side collision crashes, by covering all the windows and the pillar trim. But that's not all. Here are a few other ways these airbags can keep you and your passengers safe:

Since side curtains often cover most, if not all, of the window space, they can provide a barrier that helps prevent ejection from the vehicle [source: Safercar]. Even when seatbelts are used properly, a crash might force arms or legs through the windows and subject them to serious injury. The side curtains' internal structure is strong enough to minimize the risk of full or partial ejection. They are also able to keep out intrusions such as metal, broken glass, and other crash debris, cutting down on injuries such as broken bones, cuts and bruises.

Some curtain airbags are specifically designed to provide protection in a rollover crash, a feature first found on the Ford Explorer [source: Mello]. Airbags with this benefit feature sensors to notice if a rollover is imminent by monitoring whether the vehicle is tilting. When the bags deploy, they remain inflated longer than their non-rollover counterparts to compensate for the additional time vehicle occupants are in danger. Regular airbags deflate immediately after the impact, usually less than a second after they are deployed. Rollover protection curtains, by comparison, remain inflated for several seconds while people are being tossed around inside the vehicle, and are deployed with cold helium to maintain their volume for an extended period of time. This feature is most often found on SUVs, which are more prone to rollover incidents because of their higher center of gravity.

The reputation of traditional airbags was put at risk when children were hurt by early systems. The technology has been refined, and parents are now cautioned to keep small children away from front and side impact airbags. However, side curtains do not pose these same risks. According to the Insurance Industry for Highway Safety, children may be too small to benefit from the protection offered by a curtain-style airbag, but safety experts agree that children are safe in the presence of these airbags [source: Mello]. Unlike front and torso airbags, the curtains' deployment does not cause a high-force intrusion of the occupants' personal space.

Side curtains are designed to work as a complement to traditional airbags, not as a standalone system. Up next, learn about the different types of airbags and how they all work together to keep you safe.

As government safety standards change and the latest technology proves its efficacy, it's helpful to understand how your car's safety systems work together. Side curtains were developed as a supplemental system to offer protection where traditional airbags fell short, but traditional airbags are still essential. They can go by many names, based on original equipment manufacturer (OEM) suppliers, government regulators and auto industry marketing types, but it's important to understand the basic systems and what they do.

Frontal airbags are mounted in the steering wheel and dashboard; side protection systems are mounted in the seat frame or door, which varies according to supplier and automaker. Not all of a car's airbags will deploy in the event of a collision; the airbag system's network of sensors will determine which airbags are needed [source: WIPO]. Here are some of the main types of airbags you might find in your vehicle:

The driver airbag is the one mounted in the steering wheel that protects the driver in most crashes, including front, rear and side impacts [source: Autoliv: Driver]. If the driver is flung forward in a crash, chances are that they will be up close and personal with the driver airbag.

The passenger airbag is similar to the driver airbag and deploys under similar conditions. It is located in the dashboard on most cars [source: Autoliv: Passenger]. This airbag is dangerous for small children and can result in injury or even death.

The thorax bag is estimated to reduce severe chest injury in side impact collisions by 25 percent, according to one manufacturer [source: Autoliv: Thorax]. When deployed, it provides a barrier between the seat occupant and the door.

The head thorax bag is similar to the thorax bag, providing protection from side impact collisions [source: Autoliv: Head]. It is larger, though, to give extra protection to the head also.

The pelvis thorax bag inflates near the hips of the seat occupant to prevent lower body injury during a side impact collision [source: Autoliv: Pelvis]. This airbag is small and deploys very quickly from the seat's frame.

Side curtain airbags are becoming increasingly popular with manufacturers and consumers. Read on to learn about how much they cost and what that may mean for their availability.

Thanks to the extremely competitive nature of the auto industry and increasingly strict federal safety regulations, consumers who are interested in buying a vehicle with side curtain airbags have a lot of choices.

Cars equipped with side curtain airbags have a little emblem near the roof or pillar to identify their presence, much like those found on steering wheels, dashboards and seats. These emblems may carry the acronyms SRS (Supplemental Restraint System) or SIR (Supplemental Inflatable Restraint). Since the NHTSA's 2007 decision to increase side impact collision standards, these emblems are going to be an increasingly common sight. According to airbag manufacturer Autoliv, side curtains are available in more than 60 percent of new vehicles in North America and Europe, and that number will steadily increase until side curtains become customary to comply with the 2013 side impact standards [source: Autoliv: Inflatable Curtain ].

There are only a few major OEM suppliers of side curtain airbags, so prices are pretty consistent and profit margins for the suppliers are slim. This keeps costs down for car buyers. Side curtain airbags cost between $50 and $100 each to supply to automakers; variations in price depend mostly upon the size of the vehicle [source: Automotive News]. Large SUVs and crossovers with third-row seating will have more expensive airbags than a small sedan would, because larger airbags require more materials and sometimes use additional deployment modules. NHTSA estimates that when side curtain airbags become standard to meet the new side impact regulations in 2013, the airbags will add about $33 to the overall cost of the vehicle. [source: Benton].

Side curtains are slightly more expensive from OEM suppliers than traditional chest airbags (which cost about $50 apiece, on average) [source: Automotive News]. Since automakers all have unique ways of "bundling" safety features, the cost to consumers can vary. Except for some side impact and curtain airbags, most airbag systems aren't generally treated as a source of profit. The benefit to automakers comes in the form of positive publicity from good safety ratings.

In the next section, we'll show you some actual safety tests with and without side curtain airbags.

Vehicles are available in many different configurations to suit a customer's budget and needs. For example, optional airbags might not be a priority to a car buyer who rarely carries passengers. If you're interested in a certain car, you should read up on its crash test data. Side curtain airbag quantity alone doesn't tell the whole story -- some vehicles will use one airbag to cover all windows whereas others will use a separate airbag for each window.

We're able to see how side curtain airbags affect safety scores by studying Insurance Institute for Highway Safety (IIHS) crash tests conducted on cars with and without side curtain airbags. The IIHS notes that side impact crash test ratings can be compared across vehicle type and weight categories, but for simplicity's sake, we'll focus on comparisons of the same vehicle. The rating system follows this scale: Good, Acceptable, Marginal and Poor.

First, we'll look at a 2002-2006 Toyota Camry without side curtain airbags and a 2004-2006 Camry with side curtains. (The discrepancy in model year range reflects the addition of the side curtain airbags for 2004; though it is described on the IIHS site as "side structural changes," Toyota reported that these changes alone would not affect test results without the airbags.)

The Camry without side curtain airbags was given an overall rating of Poor. For head protection, its driver safety rating was Poor and the rear passenger rating was Marginal [source: IIHS]. But the Camry with side curtains was rated Good overall, with Good ratings for both driver and rear passenger head protection [source: IIHS].

For car buyers who've got soccer practice duty, IIHS also tested the 2006-2007 Dodge Grand Caravan. Again, side curtain airbags were responsible for an increase in driver and passenger safety. The minivan without side curtains rated Poor overall, Poor for driver head protection, and Marginal for rear passenger head protection [source: IIHS]. However, the minivan with side curtains earned an Acceptable overall rating, with Good ratings for driver and rear passenger head protection [source: IIHS].

On the next page, you'll find lots more information about airbags and other automotive safety features.