September 8, 2004
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by Jim Kerr
There is a common perception that if you are in a collision, the bigger the vehicle, the safer it will be for the occupants. It is hard to argue against this premise. Who survives if a car hits a train? How about hitting a Semi? Even between two passenger vehicles, the larger one should win, but not always. Safety technology has changed leaps and bounds in the last couple decades and now some new compact cars are safer than large vehicles were a few years ago. In fact, Mercedes is introducing a new vehicle brand this Fall in Canada that may redefine how we think of safety and small cars. The brand is called “Smart” and the first Smart models will be the fortwo cdi coupe and cabriolet.
The fortwo is appropriately named. It is a vehicle “for two” occupants. Research has shown that on average, a car carries only 1.2 occupants to work. The fortwo handles that with ease. The cdi designation is for the common rail fuel system technology used on the fortwo’s 0.8 litre three cylinder engine. It may only put out 40 horsepower but propels the car to a top speed of 135 kph and uses only 4.2 litres of fuel per 100 kilometres.
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With a length of only 2.5 metres, the fortwo is definitely compact. Two of them can fit in a standard sized parking slot! There isn’t much separating the occupants from the outside, so every part of the car plays a critical part in occupant safety. The core of the fortwo is a high-strength tridon safety cell. The safety cell acts as a shield to protect the passengers during a collision. Impact forces are directed by the safety cell to both the collapsible structure in the fortwo and to the other vehicle involved in the collision.
The structure surrounding the tridon safety cell is designed to crush during a collision. Even though the front and rear of the vehicle are very short, they can quickly absorb impact energy. The fortwo structure has undergone many crash tests. While all have shown outstanding safety results, the most impressive tests are when the fortwo is shown in a car-to-car crash with a Mercedes E-Class sedan. The E-Class car is twice the weight of a fortwo and is recognised as safe car in its own right.
The E-Class and the fortwo were tested in an offset frontal collision at 50 km/h. While you can see the front of the fortwo disappearing during the collision and the rear structure of the car collapsing, the passenger compartment stays virtually intact. Other tests the fortwo have passed include a frontal crash at 65 km/h into a deformable barrier, rear end crash at 55 km/h and a side impact at 50 km/h. In every test, the fortwo deformation values were below all internationally recognised standards (the lower the value the better).
During side impacts, forces on the fortwo are deflected away from the passengers. Because of the ultra-short wheelbase, a side impact will almost always hit a wheel and the suspension. Just like Formula 1 cars, the suspension will collapse, absorbing the impact and reducing forces on the passenger compartment.
During the impact, emergency tensioning devices pull the seatbelts tight in a few thousandths of a second, holding the passengers firmly inside the vehicle. Immediately afterwards, a belt force limiter controls the restraining force on the passengers, allowing them to decelerate gradually and reducing possible injuries from seat belt impacts. The passengers ride out the collision in a protective shell cushioned by air bags.
While passive safety is part of the design, active safety ensures the driver will be able to control the car under all conditions so that collisions can be avoided. The fortwo cdi includes ESP (electronic stability program), Brake Assist, and ABS as standard equipment. All of these systems assist the driver in maintaining control during sudden manoeuvres. A lightweight small car can stop quicker and change direction faster than a heavy one, giving the fortwo an advantage over larger vehicles. The electronics packages make these manoeuvres safer.
The fortwo has been under development since 1994 and sold since 1998 in 31 countries around the world. Now it is coming to Canada and soon to the United States. Rising fuel prices and congested city traffic in North America will undoubtedly increase interest in small economy vehicles. It is nice to know that drivers will not have to sacrifice safety when looking for economical transportation.