rollover

A rollover in Sydney, Australia on Christmas day, 2001.

Rollover is a type of vehicle accident, where a vehicle turns over on its side or roof. The main cause for rolling over is turning too sharply while moving too fast.

Dynamics

A rollover in southern Italy.

The force of inertia (acting in the direction opposite to the one it is turning) is combined with the force of gravity (acting downwards). When the combined force as applied to the centre of vehicle's mass falls outside of the rectangle formed by the wheels, the vehicle starts to turn over. A rollover can also occur as a vehicle crosses a ditch or barrier rather than a flat road surface. Such an event can be triggered by a sudden turn to avoid a collision, or a loss of traction due to water or ice.

Competition

A skilled driver may stop the fall by stopping the turn. Stunt drivers in competition deliberately use ramps to launch a car, often a short, stubby subcompact which is more easily turned over. Short of a rollover, stunt drivers may also drive the car on two wheels for some time, but this requires precise planning, control and specialized safety equipment.

Cars and SUVs

Rolled over Ford Explorer (see Firestone and Ford tire controversy)

All cars are susceptible to rollovers to various extents. Generally, the higher the centre of mass is located, the higher the vehicle is and the faster it goes, the more likely it is to roll over. Civilian SUVs are particularly notorious for rolling over because they often have a higher center of gravity due to raising the suspension to accommodate 4 wheel drive. Among the vehicles which have received publicity for rolling over are the Ford Bronco II, Suzuki Samurai, Jeep CJ, Ford E-Series and Isuzu Trooper, though NHTSA investigations have not found evidence of excessive risk compared to other similar vehicles.

HMMWVs are much wider than civilian SUVs. While more difficult to tip over deliberately, many American casualties in Iraq are caused by rollovers, with the turret gunner being particularly vulnerable in an accident. ^[1] Military jeeps with independent suspensions were prone to rollover, and not sold to civilians for this reason. Trucks can often roll over when doing sharp turns and trains can roll over after derailing.

Some four wheel drive pickup trucks have reduced steering capacity to prevent rollover. This creates problems with parking and negotiating very sharp curves. 15 passenger vans, which have raised heavy-duty suspensions and a heavy load of passengers are also prone to rollover. It is recommended to not load anything on the roof of such vans, and to use drivers trained to avoid sudden maneuvers.

A vehicle may roll over for other reasons, for example when hitting a large obstacle with one of its wheels, when manoeuvring over uneven terrain, etc.

Exit

After the rollover the vehicle may end up lying on the side or on the roof, often blocking the doors and complicating the terrifying escape for the passengers. Large passenger vehicles such as buses, trams and trolleybuses that have doors on one side only usually have special windows with handles to pull to use the window as an emergency exit or glaziers fixed near the windows for cutting the glass and making an improvised exit in case of a rollover. Some have emergency exits in their roofs.

Roll bars and cages

Rollover crashes are particularly deadly for the occupants of the vehicle when compared to frontal, side or rear crashes, because in normal passenger vehicles, the roof is likely to collapse in to the occupants and cause severe head injuries for them. The use of roll cages in vehicles would make them much safer, but in most passenger vehicles their use would cut cargo and passenger space so much that their use is not possible. The Jeep Wrangler, a vehicle which is short, narrow, and designed to be used on uneven terrain, is unusual in that it comes equipped with a roll bar as standard.

The decline in popularity of convertibles was due in part due to concern over rollover accidents, as most convertibles have no protection beyond the windshield frame. Removable roof panels provide an open roof with a roof frame. Some convertible vehicles provide rollover protection as two small bars behind the headrests. Some Mercedes convertibles have a retractable roll bar which deploys in case of an accident. Race cars almost always have roll cages, since they are likely to roll over while driven at very high speeds and through sharp corners, and the roll cage's chassis-stiffening effect is usually positive.

References

External links

• DOT rollover ratings by vehicle type (NHTSA)
• The center for auto safety videos (Rollover videos at the bottom)..
• Rollover Training, FA Style (parody WMA video clip)

See also

• Dynamic rollover
• Roll over protection structures (ROPs)

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