Time - Space Diagram

Traffic engineers also evaluate the traffic flow along a roadway using a “time-space” diagram. This two-dimensional diagram shows the position and travel path of a vehicle through time as it moves from one intersection to another.  The diagram shows multiple intersections along a corridor and provides detailed operation of each intersection as to when green, yellow and red times will occur.

The following is a sample of a time-space diagram showing the progress of vehicles along an unsynchronized corridor. Note that the vehicles stop at each intersection which causes delay, queuing and inconvenience to drivers.

Now look at the same corridor with synchronized traffic signals. Note that the vehicles may only stop at the very first intersection and then proceed through the entire length of the corridor without making any stops.

As you can see from the figures above, synchronization does not significantly change the duration of red and green times, but merely coordinates the green time of each intersection to match the arrival of vehicles.