Traffic Signal Design MCQ with answer and solution

Concept

In the alternate system, alternate signals or groups of signals along a road show opposite colours (red/green) at the same time.

Step-by-step solution

1. Recall the four types of coordinated signal systems: simultaneous, alternate, simple progressive and flexible progressive. 2. Simultaneous: all signals show the same colour at the same time. 3. Alternate: alternate signals or groups of signals show opposite colours at the same time. 4. The question says groups of signals show opposite indications at the same moment, so it is the alternate system. 5. Answer = (B).

Explanation

In the alternate system, if one signal or group shows green, the next signal or group shows red at the same time. When groups of signals change together like this, it is called the double alternate system. So clusters showing opposite indications at the same moment means the alternate system.

Why the other options are wrong

A: Simultaneous system shows the same colour at all signals at the same time, not opposite colours. C: Flexible progressive system changes the cycle and offsets automatically with time and traffic. It is not based on opposite colours. D: Simple progressive system gives green to signals one after another, with a time offset that matches vehicle speed. It is not based on opposite colours.

Shortcut

Same colour = simultaneous; opposite colour = alternate; time-offset green wave = progressive.

Common mistake

Confusing the alternate system with the simultaneous system, because both change all signals at the same instant.