Ramp Meters

Select View ➔ Ramp Meters menu item

A ramp meter is a traffic signal at an on-ramp which controls the rate of vehicles entering a freeway. Typically, one vehicle is permitted to enter for each green indication displayed on the signal.

The following operations can be performed on a ramp meter:

• Activating and deactivating meter
• Adjusting meter release rate
• Querying meter status
• Querying green counts
• Synchronizing clock
• Configuring time-of-day operation

Setup

For basic time-of-day operation, the simple metering algorithm will run the meter at a fixed release rate, equal to the target rate for the current period (AM or PM).

The density adaptive algorithm requires a bit more configuration, since it depends on the road topology. An entrance r_node must exist, with matching roadway, road_dir, cross_street, cross_dir and cross_mod. This r_node must have one green detector, plus optional queue, passage, bypass and merge detectors.

There are special rules for meters on CD roads:

• The meter's roadway must be the main road
• The entrance r_node must be on the CD road
• The name of the CD road must be the same as the main roadway, but contain the word-token "CD"

Advance warning beacons are flashing lights on a static sign, e.g. "PREPARE TO STOP WHEN FLASHING". Typically, they are hard-wired to flash when the meter is operating, but they can be controlled by IRIS if that is not feasable. In that case, beacons will also flash if a merge detector on the entrance ramp has high occupancy (30%+).

Locks

Operators can lock a ramp meter either ON or OFF by selecting a lock reason. OFF locks prevent the meter from turning on, and will stay in place until manually removed. ON locks have an expiration depending on the reason, and the metering rate can be adjusted using the Shrink and Grow buttons.