It was the worlds first safety car. Before any other manufacture made these features available. The car was rear-engined and rear wheel drive. A perimeter frame surrounded the vehicle for crash protection, as well as a roll bar integrated into the roof. The steering box was behind the front axle to protect the driver in a front-end accident. The instrument panel and all controls were within easy reach of the steering wheel, and the dash was padded for safety.[14] The windshield was made of shatterproof glass and designed to pop out in a collision to protect occupants. The car's parking brake had a separate key so it could be locked in place to prevent theft. The doors extended into the roof, to ease entry and exit.[12] Each Tucker built differed somewhat from the previous car, as each car built was basically a “prototype” where design features and engineering concepts were tried, improved, or discarded throughout the production cycle. The door releases on the interior of the Tucker came from the Lincoln Zephyr. The steering columns used in the Tucker were donated by Ford and are from the 1941 Lincoln. Preston Tucker held a patent for a collapsible steering column design. A glove box was added to the front door panels instead of the more conventional location in the dash to provide space for the “crash chamber” that the Tucker is now famous for. This is a padded area ahead of the passenger seat, free from obstructions, providing the front seat passengers an area to protect themselves in the event of an accident.[2] The engine and transmission were mounted on a separate subframe which was secured with only six bolts. The entire drivetrain could thus be lowered and removed from the car in minutes. Tucker envisioned loaner engines being quickly swapped in for service in just 30 minutes.[15]