While proceeding across the southbound two lanes of a divided 4 lane street the vehicle inexplicably braked violently to a complete stop. When stopped the vehicle was across the two lanes of the road (as I was headed for a divided left turn lane). The was traffic on the road that had to stop for my vehicle. It took a couple of seconds for the car to release the brakes and allow me to continue across the street. This could have cause a wreck if the street traffic had not been paying attention or had assumed I was going to continue as should have been expected. I had to try to hit the gear shift stock in order to get the car to continue moving, although I am not sure that the car required this action. I did not know for how long the vehicle would be immobile. I could have been injured or killed due to this ‘phantom braking’ incident.