When you cannot go faster than the car in front, and you cannot pass them but you want to, you are joining a platoon. The speed of the driver at the front of this group of cars (which engineers evoking military organization call a platoon) imposes his speed on the others. While this may seem inefficient from your perspective, it may be to your advantage. Traffic engineers coordinate traffic signals so that if you are driving the speed limit, you make a series of green lights (this is called a “green wave”). (You are less likely to get a red light.) If you are in a platoon of vehicles arriving at an intersection, you are more likely to get a green light. If more vehicles are platooned on the cross-street, you will get more green time.