Using reduced speed areas to modify desired speed

With reduced speed areas, vehicles automatically decelerate before entering the area and enter it at a reduced speed. After leaving the reduced speed area, the vehicle automatically accelerates until it reaches its desired speed again.

When entering the network, each vehicle is assigned a fractile value for speed distribution. This value remains unchanged during the entire simulation time.

As reduced speed areas are mainly used to model curves, reduced speed areas are often used for connectors between two links. For links or connectors with multiple lanes, position a reduced speed area on each lane.

A reduced speed area may extend beyond several links or connectors. To define a larger reduced speed area, specify multiple consecutive reduced speed areas that all lie on one link or connector.

When a vehicle approaches a reduced speed area, it is assigned a new desired speed. The new speed has been specified in the desired speed distribution of the respective vehicle class.

A reduced speed area only applies for vehicles of the selected vehicle classes.

Note: Do not select a vehicle class for a reduced speed area whose vehicles you want to keep a higher or lower speed when they pass the reduced speed area.

After leaving the reduced speed area, the vehicle automatically reaches its desired speed again. For this purpose, Vissim calculates a theoretical speed to account for the acceleration of the vehicle downstream of the reduced speed area. This theoretical speed is that of a free vehicle that can travel at the desired acceleration.

Assigning a reduced speed area a higher speed

You can assign a vehicle a higher than its current speed when it is approaching a reduced speed area.

• A vehicle driving faster than the vehicle class specific speed for a reduced speed area will reduce its speed when approaching the reduced speed area. So when the vehicle reaches it, it will be driving at the lower, vehicle class specific speed of the reduced speed area. Braking starts, as soon as required to reach the reduced speed. The braking deceleration value is positive.
• A vehicle driving slower than the vehicle class specific speed of the reduced speed area will only change its speed once it has reached the reduced speed area. A reduced speed area is not meant to cause a slower vehicle to accelerate to a certain speed until it reaches the reduced speed area. For slower vehicles, a reduced speed area has the effect of a higher desired speed decision and only becomes effective once the vehicle has entered the reduced speed area.

Influence of reduced speed area on delay measurement

Preceding vehicles or different network objects located further downstream might lead to a vehicle to go below its desired speed. Reduced speed areas are network objects. Going below the desired speed results in a time delay that is added to the delay. This accumulated delay also includes the time delay caused during braking before entering the reduced speed area. The time delay caused through the reduced speed area is deducted from the accumulated delay during the time step the vehicle reaches the reduced speed area. So during this time step, the accumulated delay is reduced (Showing delay measurements in lists).