The Ford LTD Crown Victoria and Chevrolet Caprice are the two standard patrol vehicles. While both companies offer similar option packages, larger departments add a great deal to their cars in the after-market, including emergency equipment, sirens, radios, and electric conveniences. Sometimes there are conflicts between demands for great performance and the need for reliability and durability. Mustangs are used by departments in 28 States as speciality high speed pursuit vehicles, while the Taurus will be touted as a vehicle with excellent maneuverability, fuel economy, comfort, and convenience. The procurement process for police cars begins with a department specification, which is submitted to car dealers for bids. Prices are considered along with performance, ergonomics, and communications. Some agencies also use complex tests to compare price to performance. Vehicle life can depend on budgetary constraints or on calculations of maintenance and operating costs.