the deck. In the event of long pipes or steel or lumber coming loose in a hard braking incident, they save the operator and cab/sleeper in one of two manners in theory. If attached to the trailer they bend while attempting to block forward motion of a loosened cargo, causing the long load to go above the cab and driver. If attached to the frame behind the cab or sleeper of the tractor, in theory, they protect the back of the cab from impact and if unable to stop the load coming through the cab, they cause the cab to be knocked off of the frame, rather than impale the cab and kill or seriously injure the driver. 48- and 53-foot lengths usually have two axles spread out to over apart at the rear "California spread" in order to allow for more weight distribution on the rear of the deck (40,000 lb instead of 34,000 for a tandem axles design). The so-called Cali spread was originally designed to comply with bridge weight formulas in that state but has since been adopted in most other parts of the country. These spread axles take a far wider turning radius, and if turning the combination tractor/trailer too sharply, the front axle tires of the trailer may damage the road/parking lot surface, or pop a tire off of the rim, or both. Some trailers have the capability of lifting or lowering the front axle independently to mitigate this risk. The driver may not be able to use this feature if the trailer is loaded, but if the deck is empty the driver can lower the front axle to bring the rear axle off of the ground to significantly decrease the turning radius of the rig for easy maneuvering in tight spaces, or to reduce tire wear during empty/deadhead miles of travel. Under the deck of the trailer can be attached racks for spare tires, dunnage boards, or tire chains, as well as various tool/storage boxes. On one side (or often both sides for alternating pull-on strap tension) are usually sliding (but sometimes fixed) winches to ratchet down 4-inch straps for load securement. On most 48-foot trailers, these strap/winches may not be placed over a tire as when air pressure releases out of the suspension system when parked, the deck lowers down and will likely pop a trailer tire. Some trailers have an air scale.