41.5.1 - Effective green time
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Introduction to Effective Green Time
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Today, we're going to learn about effective green time. Can anyone tell me what they think effective green time means?
Is it just the amount of time the light is green for cars to go?
Yes, but it's more than that! Effective green time includes the actual green light, plus the yellow and the all-red durations, adjusted for lost times. So, if we think about it, it’s key to ensuring smooth traffic flow.
But how do we calculate it?
Great question! We use the formula: g = G + Y - L, where G is the green time, Y is yellow and all-red times, and L is lost times. Can anyone remind us what lost time includes?
Lost time includes things like startup lost time and clearance lost time, right?
Exactly! That's a perfect summary. If we understand effective green time, we can better manage the flow of traffic.
Now, summarizing: effective green time is crucial for traffic flow and calculated with g = G + Y - L. Keep that in mind!
Application of Effective Green Time
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Let's talk about lane capacity. Who can explain how effective green time affects it?
Isn't lane capacity how many cars can move through in an hour?
Yes! And it's calculated using the effective green time in relation to the saturation flow rate. When the signal is green, we can use the formula: c = (g / C) * s. Can someone tell me what each variable represents?
g is the effective green time, C is the cycle time, and s is the saturation flow rate.
Exactly! This calculation helps us estimate how well we can manage the vehicles at an intersection.
In summary: Effective green time influences capacity through the formula c = (g / C) * s.
Examples and Case Studies
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Let’s look at a case study. Assume we have 30 seconds of green time, 5 seconds for yellow and all-red combined, with 3 seconds of lost time. What would the effective green time be?
So, using the formula, I would calculate g = 30 + 5 - 3, which equals 32 seconds.
Great job! Now, how would we apply this to find lane capacity if the saturation flow rate is 1200 vehicles per hour?
Using c = (g / C) * s, we would need to know C. If C is 60 seconds, then c = (32 / 60) * 1200.
Correct! Can anyone compute that?
That would be 640 vehicles per hour!
Well done! This illustrates the significance of effective green time in real situations.
In summary: Always use the effective green time in your calculations to improve lane capacity accurately.
Introduction & Overview
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Quick Overview
Standard
Effective green time integrates the actual green indication, the yellow change interval, and the all-red clearance interval, adjusted for respective lost times. This concept is crucial for determining the optimal traffic flow through an intersection, enhancing signal efficiency.
Detailed
Effective Green Time
Effective green time is a key concept in traffic signal design, representing the total time during which vehicles can move through an intersection without stopping. It is calculated as the sum of the actual green time and the durations of the yellow change interval and the all-red clearance interval, minus any applicable lost times. The equation used to define effective green time (g) is as follows:
$$g = G + Y - L$$
Where:
- G = Actual green time
- Y = Yellow and all-red times
- L = Lost times (including startup and clearance lost times)
Understanding effective green time is crucial for determining lane capacity and ensuring that the traffic flow remains smooth and efficient at signalized intersections.
Moreover, effective green time directly influences the capacity of a lane by allowing for accurate calculations of the saturation flow rate, ensuring that the signal timings are optimized for real-world conditions.
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Definition of Effective Green Time
Chapter 1 of 2
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Chapter Content
There is another concept to find the amount of greentime available. This is called effective green time. It is the sum of actual green time (G) plus the yellow and all red times (Y) minus the applicable lost times. This lost time is the sum of start-up lost time (l1) and clearance lost time (l2). Thus effective green time can be written as,
g = G + Y - L
Detailed Explanation
Effective green time refers to the actual time during which vehicles can move through an intersection without stopping. It consists of three components: the actual green time (when the light is green), the yellow time (the transition period before the light turns red), and the all-red time (when all lights are red) minus any lost time due to delays, such as the time taken for vehicles to start moving when the light turns green and the time needed to clear vehicles from the intersection after the light turns red.
Examples & Analogies
Imagine you are at a traffic light. When the light turns green, you don’t immediately start moving; you wait for a moment to check if it’s safe. This waiting time is part of the lost time. Effective green time considers how much time is actually available for cars to clear the intersection, factoring in not just the green light but also the time taken to react and start moving.
Calculating Effective Green Time
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Chapter Content
Effective green time can be mathematically expressed as:
g = G + Y - (l1 + l2)
where, l1 = start-up lost time and l2 = clearance lost time.
Detailed Explanation
When calculating effective green time, you take the total time the light is green (G), add the duration of the yellow light (Y), and then subtract the total lost time, which includes: l1, the time lost at the start when the green light comes on as drivers react; and l2, the time lost for vehicles to clear the intersection when the light turns red. This gives you the net time that can effectively be used for vehicles to pass through.
Examples & Analogies
Think of a classroom setting where the teacher allows students to leave at the end of class. The time from when the bell rings (green light) to when the last student leaves (effective green time) will depend on how quickly students respond to the bell (start-up lost time) and if everyone is out before the next class starts (clearance lost time).
Key Concepts
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Effective Green Time: Total available green light duration adjusted for lost time.
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Lost Time: Time that does not contribute to the effective usage of the green time.
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Lane Capacity: The maximum number of vehicles that can be accommodated during the green time.
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Saturation Flow Rate: The maximum flow rate of vehicles through a lane when the signal is green.
Examples & Applications
If a signal has 30 seconds of green time, 5 seconds of yellow and all-red times, and 3 seconds of lost time, the effective green time would be calculated as 30 + 5 - 3 = 32 seconds.
For an intersection with a cycle time of 60 seconds and a saturation flow rate of 1200 vehicles/hour, effective green time of 32 seconds could support a lane capacity of 640 vehicles/hour.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
When the light goes green, it’s time to be seen; with yellow and red, don’t lose your head!
Stories
Imagine a race where cars wait on green. When the light changes, they zoom ahead, but everyone loses a few seconds at the start—this is lost time.
Memory Tools
Remember 'GLY' for calculating effective green time: G for green, L for lost time adjustments, Y for yellow clearance.
Acronyms
Use 'EGT' to remember Effective Green Time
meaning Effective
for Green signal time
and T for Time adjusted.
Flash Cards
Glossary
- Effective Green Time
The total time available for vehicles to move during a traffic signal cycle, calculated as the sum of actual green time and yellow clearance time minus lost times.
- Lost Time
The time that does not contribute to the effective use of the green time, including startup lost time and clearance lost time.
- Cycle Length
The total time taken for a complete cycle of traffic signal indications, denoted as C.
- Saturation Flow Rate
The theoretical maximum number of vehicles that can pass through a lane during green time, typically measured in vehicles per hour.
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