How a bus can ask for more green time
A signal-priority system links a bus’s location to the traffic signal ahead. GPS can show that the bus is nearing an intersection; that arrival information gives the signal controller time to adjust its timing. If conditions allow, it can keep the current green on a little longer or bring the bus’s green phase forward by shortening some of the waiting time on another phase.
That is different from simply switching every conflicting light to red the instant a bus appears. Signals still have to provide safe intervals for vehicles and pedestrians to clear the intersection. Priority is a controlled adjustment to the signal cycle, not permission to ignore it.
Why the adjustment matters on a busway
A brief stop at a red light can disrupt more than one bus. TransMilenio buses carry many passengers, and a delay at an intersection can leave following buses bunched together: one arrives late, while another catches up behind it. Helping a bus pass through a signal can reduce that interruption and make service more regular.
The benefit is not unlimited. A signal cannot grant every approaching bus a green without delaying cross traffic, and priority works only where the equipment and timing permit it. The tradeoff is deliberate: a small adjustment for a heavily used bus can move many people through an intersection, while the cross street may wait a little longer. That is the practical meaning of giving transit priority—not making the bus invincible, but reducing the time it loses to the same signal cycle as everyone else.
