Air carrier Captain reported a near miss with a vehicle during taxi approaching the gate.

Narrative

Near-miss with ground vehicular traffic on airport proximate to gate XX. Approaching gate XX for parking; it was apparent that there was not a crew in position to guide the aircraft to the gate. The aircraft was stopped with the parking brake set on the ramp positioned slightly beyond the painted lanes for vehicular traffic while waiting for the guide person and wing walkers. Announcement made to the crew and customers reminding that we were not yet at the gate and to please remain seated with seat belts fastened until the seat belt set sign was turned off. Once ground crew got in position; we started moving to the parking spot. Seemingly; out of nowhere a vehicle in the painted travel lane; sped from left-to-right toward the aircraft nose. I closely assessed whether or not the vehicle would/could stop. It did not slow down; so I took evasive action by slamming the brakes and abruptly stopping the aircraft. The vehicle disappeared from my field of view below the left window rail/glareshield/nose of the aircraft and emerged in the First Officer's field of view out his right window. The vehicle apparently never slowed down.Cause: Lack of command or control of ground vehicle traffic on the ramp.