Vehicle rollover: Difference between revisions

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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

Vehicles usually roll over due to one of several mechanisms. These are excessive cornering, tripping, collision with another vehicle or object, or traversing a critical slope.

Excessive cornering rollovers occur when cornering forces destabilize the vehicle. As a vehicle rounds a corner, three forces act on it: tire forces, inertial effects, and gravity. The cornering forces from the tire push the vehicle towards the center of the curve. This force acts at ground level. The force of inertia acts horizontally through the vehicle's center of mass in the direction opposite to the one it is turning. These two forces make the vehicle roll towards the outside of the curve. The force of the vehicle's weight acts downward through the center of mass in the opposite direction. When the tire and inertial forces are enough to overcome the force of gravity, the vehicle starts to turn over. Most passenger vehicles will slide or spin before this happens, but this is a common type of rollover for taller vehicles, including light trucks (SUVs, vans and pickup trucks), busses and heavy trucks.

Tripping rollovers occur when a vehicle is sliding sideways, and the tires strike a curb, dig into soft ground, suddenly regain traction, or a similar event occurs that results in a sudden lateral force. The physics are similar to cornering rollovers.

A collision with another vehicle or object can cause a rollover. These occur when the collision causes the vehicle to become unstable, such as when a narrow object causes one side of the vehicle to accelerate upwards, but not the other, causing the vehicle to rotate along its long axis. A side impact can accelerate a vehicle sideways. The tires resist the change, and the coupled forces rotate the vehicle. In 1983, crash tests showed that light trucks were prone to rolling over after colliding with certain early designs of guide rail.^[1]

A rollover can also occur as a vehicle crosses a ditch or slope rather than a flat road surface. Slopes that are steeper than one unit vertically for every three units horizontally are termed 'critical slopes' and often contribute to rollovers.

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.

Rollover contest

The driver deliberately drives their vehicle to a ramp which causes their vehicle roll over.^[2] The winner is the driver who guides their vehicle to the most rolls.^[2]

Cars and trucks

File:Xploder.jpg

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, and the more sensitive the steering 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, Mitsubishi Pajero/Montero, and Isuzu Trooper.

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. ^[3] 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. Passenger vans which have raised heavy-duty suspensions and are used with 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 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 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

^ http://engineering.unl.edu/specialty-units/MWRSF/MwRSF-Downloads/MGS/TRR%202025%20Paper%2007-2642.pdf Kaller, Sicking et al, Performance of Steel-Post, W-Beam Guardrail Systems, 2007,
^ ^a ^b "Race Descriptions: Rollover Contest". Evergreen Speedway. 2006-03-26. Retrieved 2008-08-07.
^ [1] "Iraq rollover kills Oregon soldier" Oregonian May 25, 2005 by MIKE FRANCIS

@@ Line 34: / Line 34: @@
 == 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, [[tram]]s and [[trolleybus]]es that have doors on one side only usually have special windows with handles to pull to use the window as an emergency exit or [[glazier]]s 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.
+After the rollover the vehicle may end up lying on the side or on the roof, often blocking the doors and complicating the escape for the passengers. Large passenger vehicles such as buses, [[tram]]s and [[trolleybus]]es that have doors on one side only usually have special windows with handles to pull to use the window as an emergency exit or [[glazier]]s 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 ==