2WD until the GMT400 was phased out. The original prototype had rear disc brakes based on the B-body 9C1s whereas the production Z56s came with rear drum brakes. Plans for outfitting the Tahoe with the Z56 police package originated around the 1994 model year when GM broke news about phasing out its B-platform sedans (Caprice, Impala SS, Roadmaster) at the end of the 1996 model year where a replacement was imminent since GM ended production of its body-on-frame passenger sedans due to SUV sales. Since the introduction of the GMT900, Chevrolet currently offers two versions of the police package Tahoe; a four-wheel-drive version and a two-wheel-drive version. Just like the GMT400 based models civilian GMT800 Tahoe base & LS models were also used for police use until the Z56 police package option was reintroduced in 2004 late in the GMT800's life cycle by some agencies. Chevrolet refers to the four-wheel drive (4WD) version as "Special Service Vehicle" (SSV) which has the 5W4 code. This version of the Tahoe can be used for all purposes except pursuits and high speed responses due to its high center of gravity just below the front window (height, not location), thus having a higher probability of rolling-over at high speeds. This version is preferred by agencies where snow, ice, flooding, rough terrain, and ground clearance are common issues.[34] Chevrolet refers to the two-wheel drive (2WD) version—also known as the rear-wheel drive (RWD) version—as "Police Pursuit Vehicle" (PPV). This version be used for all purposes including pursuits and high speed responses. The center of gravity in this vehicle is lower than that of the four-wheel-drive version and the ground clearance is about 1 in (25 mm) less, with a standard rear bumper replacing the tow hitch on civilian Tahoes. Highway patrol agencies prefer the two-wheel-drive version, where pursuits and long distance responses are more common. As of the 2012 model year, the Tahoe was the last body-on-frame, rear-wheel drive police vehicle manufactured for the United States market since Ford phased out its aging Panther platform, the Volvo XC90-based Ford Police Interceptor (known as the Ford Explorer in civilian trim). Other SUVs like the Ford Expedition are used by many law enforcement and EMS agencies, but are not pursuit rated.[35] Chevrolet built a 2015 Chevrolet Tahoe Police Patrol Vehicle that was previewed as a concept at the 2013 SEMA Show in Las Vegas. The vehicle became available