NASCAR racers all drive stock cars, which are stripped down versions of normal road cars whose design features are intended to maximize speed and acceleration, over handling. Various NASCAR rules need to be incorporated into the shape of the vehicle. In total, NASCAR stipulates that 30 templates need to be designed and fitted according to precise measurements. These templates cover the basic body panel to produce a vehicle which is one smooth, solid shape. The car's doors don't open and drivers slide in through the window. As weight is reduced to an extreme minimum, the interior is reinforced by metal bars to protect their structure in the event of an accident. The light, sleek vehicles would be uncompetitive if they were slowed down too much by drag NASCAR drivers will usually be seen racing in close proximity, where things get remarkably slippery and unstable. In such turbulence, cars weighing 3,300 lbs (driver included), travelling at speeds of up to 200 mph are prone to spectacular airborne crashes.