how can freeways detect how congested the freeway is? just wondering...?

Answer 1

Some are being set up with monitoring equipment. One of which people in their homes with Cable can use to Watch a section of Freeway on their Television.

There are also speed, sensor, and weight detectors. But it depends on the Freeway (they have to be installed).

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Answer 2

There are sensors embedded in the roadway that detect vehicles passing over them. When traffic is moving normally, the sensors, which detect metal, show momentary contact when cars pass over them. When traffic backs up, vehicles pass over the sensors more slowly, causing a longer response. This info goes to a traffic control center, and warnings can be posted on electronic road signs. These days, more and more info is gathered using video surveillance. The image of particular highway trouble spots can be monitored at the same control center.

Answer 3

Typically there are one or two inductive loops embedded into the road. These can count cars passing overhead, the time each car spent over the sensor, and vehicle speed. Thus, when congestion occurs, the data will show lower speeds and more time spent over a sensor.
Sometimes agencies use CCTV cameras, but these are typically for monitoring accidents.

Answer 4

When I lived in San Diego, the DOT used cameras to keep an eye on the traffic congestion!

Answer 5

Overhead sensors measure the number of cars passing beneath and their speed. High volume and/or very low speeds indicate congested traffic.