CHAPTER 2. OPTIMIZATIONANDADAPTATIONOFTRAFFICLIGHTS7
the cars. When κi reaches a threshold θ, the green light at the same
intersection turns yellow, and the following time step it turns red with
κi = 0, while the red light which counted turns green.
The sotl-request method has no phase or internal clock. Traffic lights
change only when the given conditions are met. If there are no cars
approaching a red light, the complementary one can stay green. How-
ever, depending on the value of theta, high traffic densities can trigger
the lights to switch too fast, obstructing traffic flow.
Sotl-phase control
The sotl-phase method differs from sotl-request by adding the fol-
lowing constraint: A traffic light will not be changed if the number
of time steps is less than a minimum phase, that is, φi < φmin. Once
φi ≥ φmin, the lights will change when κi ≥ θ. This prevents the fast
switching of lights.
Sotl-platoon control
The sotl-platoon method adds two further restrictions to sotl-phase to
regulate the size of platoons. Before changing a red light to green, it
checks if a platoon is not crossing through, in order not to break it.
More precisely, a red light is not changed to green if on the crossing
street there is at least one car approaching within ω patches from the
intersection. This keeps crossing platoons together.
The second restriction is: Restriction one is not taken into account if
there are more than μ cars approaching the intersection.