Unmarked Cruiser

The Vapid Unmarked Cruiser is, hence the name, an unmarked police sedan featured in Grand Theft Auto V.

Design
The vehicle is based on the second-generation Stanier, much like the Police Cruiser, Sheriff Cruiser, and Taxi. It is in five colors with black trim and has no exterior markings, which is supposed to make it harder to be detected as a police vehicle by civilians and to offer some degree of anonymity to officers. The five colors are Black, Grey, Silver, Dark Red, and Dark Blue. It is operated by the Los Santos Police Department.

Grand Theft Auto V
According to the Rockstar Games Social Club website, the Unmarked Cruiser has similar performance to the Police Cruiser, which means a decent top speed with average handling, decent braking, average acceleration, and great durability thanks to its body-on-chassis construction. Apart from a slightly higher top speed due to reduced drag, the vehicle performs identically to its marked counterpart.

It is powered by what is modeled as a Double Overhead Camshaft Inline-4, in an front engine, rear wheel drive configuration. The engine is laid longitudinally.

Grand Theft Auto V

 * One way to obtain the vehicle is to do Barry's Weed Stash missions. Go to the highlighted green marker on the map, and some police in an Unmarked Cruiser will be waiting to ambush the player. Kill the cops and save it at a safehouse or garage. It comes in different colors (red, grey, silver, blue, light blue). The police will not pursue the player until they enter the vehicle required by Barry, meaning that obtaining the Unmarked Cruiser in this fashion is incredibly easy.
 * Property Management: when Franklin is asked to drive a Smoke on the Water van he will occasionally be chased by an Unmarked Cruiser. If the player has to deliver the car to the shop and there is no time limit countdown on screen they can be sure there is a Cruiser parked nearby which can be obtained if they take out the two officers inside.
 * 2-4 officers patrol the train station at night from 22:00 - 04:00.
 * Can rarely be seen pursuing NPC cars near LSPD Auto Impound.

Grand Theft Auto Online

 * Ambushes the player in certain cargo missions after collecting the cargo vehicle. This has been confirmed when picking up 1 crate, whether they appear when collecting 2 or 3 is currently unknown.

Trivia

 * Contrary to popular belief, this vehicle isn't exactly an undercover vehicle, just unmarked. Due to the fact that it shares the design with the Police Cruiser and Sheriff Cruiser, the vehicle is still equipped with the door search lamps, which is not unusual for an unmarked vehicle but is rather rare for an undercover vehicle. The Unmarked Cruiser also has a pushbar, which is not all too uncommon on vehicles of its type. The rear of the vehicle is still marked as "Police Cruiser", which is correct because it is simply an unmarked model of the Stanier Police Cruiser.
 * However, the siren positions are almost exactly as the ones seen in the FIB Buffalo, misleading to be at the same role.
 * The rear emergency lights, inside the vehicle, are actually a different shade of red and blue than any other LED lights in the game.
 * Uniformed officers patrol in this vehicle around the train station, which means it is sometimes used as an unmarked traffic enforcement vehicle.

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