Understanding Alternate Traffic Signal Systems

The question describes a specific type of traffic signal coordination system. It focuses on how signals along a route display indications simultaneously, specifically mentioning that clusters of signals show opposite indications at the same moment. Let's analyze the options to determine which one fits this description.

What is an Alternate System?

An alternate system is a traffic signal timing method used to coordinate traffic flow along a street or route. In this system, signals are timed such that adjacent signals or groups of signals display opposite indications simultaneously. For example, while one signal (or a block of signals) is green, the next signal (or block of signals) is red, and vice versa. This creates alternating green and red sections along the route.

The primary goal of the alternate system is to allow continuous traffic flow at a predetermined speed, known as the design speed or speed of progression. Vehicles starting at the beginning of a green wave at one signal can theoretically proceed through subsequent signals without stopping, provided they maintain the design speed.

Comparing Signal System Types

Let's look at how the alternate system compares to other types of signal coordination systems mentioned in the options:

• Simultaneous System: In this system, all signals along a route show the same indication (e.g., all green, then all yellow, then all red) at the same time. This is simple to implement but can lead to frequent stops and is generally not efficient for through traffic progression.
• Simple Progressive System: This system times signals sequentially to create a "green wave" that travels along the route in one direction. Signals turn green one after another at intervals calculated based on the desired speed and distance between intersections. It aims for continuous flow in one direction.
• Flexible Progressive System: This is an advanced type of progressive system that can adjust timing plans based on traffic conditions (e.g., different timings for peak hours, off-peak hours, different directions) and can often achieve progression in both directions, although the speeds might differ. Like the simple progressive system, it creates a green wave, but it's more adaptable.
• Alternate System: As discussed, this system features alternating green and red indications between adjacent signals or blocks of signals at any given moment. This directly matches the description provided in the question: "clusters of signals along a route display an opposite indication at the same moment".

Based on the comparison, the alternate system is the one characterized by adjacent signals or groups of signals displaying opposite indications simultaneously.

Conclusion

The system of signal in which clusters of signals along a route display an opposite indication at the same moment is called the alternate system. This method uses alternating green and red phases between signal groups to facilitate traffic flow at a specific speed.

Revision Table: Traffic Signal Systems

Additional Information on Signal Coordination

Traffic signal coordination systems are essential for managing traffic flow on urban road networks. The choice of system depends on various factors, including:

• Spacing between intersections.
• Traffic volume and direction distribution.
• Desired speed of traffic progression.
• Need for flexibility and adaptability.

Effective signal coordination reduces travel time, fuel consumption, and emissions, while also improving safety by reducing the number of stops and potential conflicts at intersections. While the alternate system is one method, modern traffic management often utilizes more complex progressive or actuated systems that dynamically adjust timings based on real-time traffic data.