my approach is not to send police cars and ambulances to patrol in the city Instead putting number of police cars and ambulances to be in Stand-by mode in certain locations in the city. Like: in parking area or the port area. When there are cases, you simply send these stand-by vehicles to the locations. This works for me and is very effective. Since patrol vehicles often blocked the traffic while they are turning into the main street. Just try to see if my method helps.