I don’t understand how they work, what they’re hooked up to and how they know when to turn from green, to yellow, to red. Are they timed? Is there a sensor, perhaps a small man hiding in the pole controlling it?
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In the lanes in front of a light, you will often see a wide, thin circular groove carved into the pavement. There will often be more than one, placed roughly where each car in line would stop if they were waiting for the light.
These grooves hold a large hoop of wire with a small bit of electric current in it. (Sometimes it’s hidden under the pavement better and you can’t actually see it.) The current in the wire bounces back and forth in a set time. However due to the laws of physics, if a large bit of metal is sitting over the wires (like a car), the current will bounce back and forth with slightly different timing. This is how the light knows a car is stopped there, which lane it’s stopped in, and how many cars are waiting.
Many people think these are “pressure“ sensors, but that would require the sensor and the pavement itself to actually have moving parts, which would be too fragile and expensive to maintain over time, and most cars’ wheels would “miss” them anyway.
From this information, the light is programmed to give preference to the cars waiting in one direction versus others, how long it should hold that light green for, and everything else. It might even vary by time of day, depending on which direction of traffic has the most cars at rush-hour or similar.
Or sometimes, especially in a rural area where the traffic does not need to be controlled so tightly to avoid backups, there are no sensors at all, and the light just runs on a simple timer to save money.
There is one controller for the entire intersection. In simplest case, its just cycling through preset states on a timer.
The complexities happen when there is need to modify that pattern on the fly. Syncing with other intersections across the city, passing emergency vehicles, buttons for pedestrians, induction sensors for cars or busses, active citywide control to unravel a traffic jam, the sky is the limit how complicated you can make it.
Stoplights work pretty much like you’d want them to at least in some states/municipalities. The expense of creating and maintaining a highway system in big cities where it is most expensive justies a suitably high tech strategy for using stop lights to maximize traffic throughput under diverse situations. How exactly? How would you do it …?
There is one controller for the entire intersection. In simplest case, its just cycling through preset states on a timer.
The complexities happen when there is need to modify that pattern on the fly. Syncing with other intersections across the city, passing emergency vehicles, buttons for pedestrians, induction sensors for cars or busses, active citywide control to unravel a traffic jam, the sky is the limit how complicated you can make it.
In the lanes in front of a light, you will often see a wide, thin circular groove carved into the pavement. There will often be more than one, placed roughly where each car in line would stop if they were waiting for the light.
These grooves hold a large hoop of wire with a small bit of electric current in it. (Sometimes it’s hidden under the pavement better and you can’t actually see it.) The current in the wire bounces back and forth in a set time. However due to the laws of physics, if a large bit of metal is sitting over the wires (like a car), the current will bounce back and forth with slightly different timing. This is how the light knows a car is stopped there, which lane it’s stopped in, and how many cars are waiting.
Many people think these are “pressure“ sensors, but that would require the sensor and the pavement itself to actually have moving parts, which would be too fragile and expensive to maintain over time, and most cars’ wheels would “miss” them anyway.
From this information, the light is programmed to give preference to the cars waiting in one direction versus others, how long it should hold that light green for, and everything else. It might even vary by time of day, depending on which direction of traffic has the most cars at rush-hour or similar.
Or sometimes, especially in a rural area where the traffic does not need to be controlled so tightly to avoid backups, there are no sensors at all, and the light just runs on a simple timer to save money.
For the most part they’re simply timed. For timed stoplights a lot of different methods that fall under the field or transport engineering are used to determine what the expected traffic load will be at any given street, and traffic lights were timed accordingly. This means that not all stoplights have the same duration to prioritise flow of traffic and optimise it.
However since this isn’t a perfect system because usually the timing is on a fixed loop which may not account for variable traffic conditions. This is why stoplight sensors are also used on many stoplights. The most common ones are induction loops, that being wires embedded in the asphalt that can detect when a car is waiting at the stoplight. However in higher traffic areas, radar, camera or other types of sensors are employed to calculate the overall number of cars on the road to try to adjust stoplights more dynamically and help optimise traffic flow in times of heavy traffic. Stoplight sensors are also handy in places with very little traffic, where usually there’s a main road with most of the area’s traffic passing through and the roads connecting to it have comparatively very little traffic. Stoplights on those connecting roads will have sensors and will only turn green if they detect a car waiting at the stoplight, otherwise they remain red so that the main road maintains a steady traffic flow. This is a better alternative to not having stoplights at all because even if those roads are low traffic that’s exactly the kinds of conditions that make people not pay as much attention as they should or going over the speed limit.
Stoplights work pretty much like you’d want them to at least in some states/municipalities. The expense of creating and maintaining a highway system in big cities where it is most expensive justies a suitably high tech strategy for using stop lights to maximize traffic throughput under diverse situations. How exactly? How would you do it …?
For the most part they’re simply timed. For timed stoplights a lot of different methods that fall under the field or transport engineering are used to determine what the expected traffic load will be at any given street, and traffic lights were timed accordingly. This means that not all stoplights have the same duration to prioritise flow of traffic and optimise it.
However since this isn’t a perfect system because usually the timing is on a fixed loop which may not account for variable traffic conditions. This is why stoplight sensors are also used on many stoplights. The most common ones are induction loops, that being wires embedded in the asphalt that can detect when a car is waiting at the stoplight. However in higher traffic areas, radar, camera or other types of sensors are employed to calculate the overall number of cars on the road to try to adjust stoplights more dynamically and help optimise traffic flow in times of heavy traffic. Stoplight sensors are also handy in places with very little traffic, where usually there’s a main road with most of the area’s traffic passing through and the roads connecting to it have comparatively very little traffic. Stoplights on those connecting roads will have sensors and will only turn green if they detect a car waiting at the stoplight, otherwise they remain red so that the main road maintains a steady traffic flow. This is a better alternative to not having stoplights at all because even if those roads are low traffic that’s exactly the kinds of conditions that make people not pay as much attention as they should or going over the speed limit.
For the most part they’re simply timed. For timed stoplights a lot of different methods that fall under the field or transport engineering are used to determine what the expected traffic load will be at any given street, and traffic lights were timed accordingly. This means that not all stoplights have the same duration to prioritise flow of traffic and optimise it.
However since this isn’t a perfect system because usually the timing is on a fixed loop which may not account for variable traffic conditions. This is why stoplight sensors are also used on many stoplights. The most common ones are induction loops, that being wires embedded in the asphalt that can detect when a car is waiting at the stoplight. However in higher traffic areas, radar, camera or other types of sensors are employed to calculate the overall number of cars on the road to try to adjust stoplights more dynamically and help optimise traffic flow in times of heavy traffic. Stoplight sensors are also handy in places with very little traffic, where usually there’s a main road with most of the area’s traffic passing through and the roads connecting to it have comparatively very little traffic. Stoplights on those connecting roads will have sensors and will only turn green if they detect a car waiting at the stoplight, otherwise they remain red so that the main road maintains a steady traffic flow. This is a better alternative to not having stoplights at all because even if those roads are low traffic that’s exactly the kinds of conditions that make people not pay as much attention as they should or going over the speed limit.
Stoplights work pretty much like you’d want them to at least in some states/municipalities. The expense of creating and maintaining a highway system in big cities where it is most expensive justies a suitably high tech strategy for using stop lights to maximize traffic throughput under diverse situations. How exactly? How would you do it …?
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