SIGNAL SYSTEMS AND SUBSYSTEMS Tapan K. Datta, Ph.D., P.E.

System-Subsystem Signal System All interconnected signals in an area can be classified as a system 1. Ability to work synchronously 2. Under same road agencies control

Subsystem Part or a small system which should work in relation to each other 1.Similar traffic characteristics 2.Homogeneous geometry 3.Homogeneous roadside development 4.Limited land area

1. Can provide break in progression in the minor streets if it does not carry heavy traffic 2. Establish priorities by road segments based on Traffic volumes Importance in carrying in and out traffic from activity centers Establish subsystems and subsystem priorities Establish road segment priorities within each subsystem

Subsystem Design Breaking a large network into smaller subsystems or zones Achieving a reasonable progression with a feasible speed There are concerns in subsystem design depending on the network characteristics

“Many of the potential benefits from signalizing intersections are realized only when a number of them along an arterial (or in a grid) are coordinated and progressive movement of platoons of vehicles is achieved.” NCHRP 172 Comments

Benefits of Progression Reduction in stops Reduction in delays Reduction in fuel consumption Reduction in pollutant emissions

Example of Farmington Hills Entire city contains 110 signalized intersections Divided into 14 zones Existing system uses 6 different cycle lengths from zone to zone and even within zone Out of 14 subsystems (zones), 7 contain less than or equal to 3 signalized intersections

City of Farmington Hills 13 MILE FARMINGTON 14 Mile 12 Mile Halsted Drake Farmington 9 Mile 8 Mile Gill Power 10 Mile 11 Mile Inkster Shiawassee Grand River Orchard Lake Middlebelt Northwestern Freedom Tuck M 5 Grand River Folsom Hills Tech Carson Walnut Lane Bayberry/Heatherstone OCC Heritage Park Fractional District School Mayfair Chester brook Det.Baptist Church Pebble Creek Gray Field East Middle School ZONE 1 ZONE 2 ZONE 3 ZONE 6 ZONE 10 ZONE 14 ZONE 9 ZONE 8 ZONE 12 ZONE 4 ZONE 5 ZONE 11 ZONE 7 ZONE 13

Portion of the Network Drawn in Synchro

How Synchro Assigns a Subsystem Command: Optimize > Partition Network Synchro partitions the network Disadvantage: Cycle lengths assigned by Synchro are not same or multiple of the minimum cycle length

Cycle lengths are not same along the arterial street.

When the cycle lengths of intersections along an arterial of the network is not same or multiple of the minimum cycle length, the progression can not be attained. Comment on Synchro Output

In order to attain progression, the cycle length needs to be assigned manually, instead of using Synchro output. Progression should be verified with the assigned cycle lengths. Using the offset at an intersection for an arterial, the offset for the cross street at the same intersection should be determined. How to solve this problem?

Assigning Cycle Lengths Manually in Synchro Assigned cycle lengths of 60 sec and 120 sec along 14 Mile Road