On optimal ramp control of traffic jam queues

Figure 1 depicts two parallel roads, one "fast" and the other "slow", with a ramp on which vehicles from the slow roadway may be allowed to merge onto the fast road. Such a situation occurs frequently when a freeway or expressway is accompanied by a service road. It seems reasonable to restrict the ramp flow when an accident or congestion has caused a traffic jam downstream from the ramp. The traffic jam will then clear up more quickly, at the expense of inconvenience to a few vehicles which must continue travelling on the slow road instead of entering the fast road. This policy is especially valid if the fast road has more high priority vehicles, e.g., buses.