light, easy to maneuver body. In recent years the value of early Land Rovers and Range Rovers has risen to the extent that this is no longer practical. CCV trailers now usually base their vehicles around Land Rover 90s or a standard 100-inch chassis from a Range Rover or Series I Discovery. The Suzuki SJ series of vehicles also make good bases for CCV-spec vehicles. Some vehicles are specially built, taking the form of light "buggies" with tractor tires and "fiddle" brakes for the best performance. Vehicles are required to meet certain safety regulations. Roll-cages must be fitted and be built to a suitable standard, recovery points must be fitted front and rear and fuel tanks must meet certain standards. A 4-point harness for all occupants is required and a fire extinguisher is recommended. Off-roading events In some countries off-road activities are strictly regulated, while others promote cross country off-road endurance events like the Dakar Rally, Spanish Baja, Africa Eco Race, Abu Dhabi Desert Challenge, Russian Baja Northern Forest, San Felipe 250 and Baja 500 & 1000, which are a test of navigation skills and machine durability. off-road parks and motocross tracks also host several events and maybe the only legal place to off-road in the area. Criticism of ORV use Environmental impact Off-road vehicle use on public land has been criticized by some members of the U.S. government and environmental organizations including the Sierra Club and The Wilderness Society. They have noted several consequences of illegal ORV use such as pollution, trail damage, erosion, land degradation, possible species extinction, and habitat destruction which can leave hiking trails impassable. ORV proponents argue that legal use taking place under planned access along with the multiple environment and trail conservation efforts by ORV groups will mitigate these issues. Groups such as the Blueribbon Coalition advocate Treadlightly, which is the responsible use of public lands used for off-road activities. According to the U.S. Forest Service the use of old-style two-stroke engines, previously common in vehicles designed for off-road use, also causes concerns about pollution. This is because "two-stroke engines emit about 20 to 33 percent of the consumed fuel through the exhaust" (as the engine lubricant is a "total loss system" and is emitted by design) and "discharge from two-stroke snowmobile engines can lead to indirect pollutant deposition into the top layer of snow and subsequently into the associated surface and ground water".