Real-time traffic information - Roadway sensors and data probes

Managing freeway traffic requires data and lots of it. The primary source of data used to understand traffic patterns are vehicle detectors. There are different types of roadway sensors based on different technologies such as microwave, audio or video detection techniques. 

Currently, the Wisconsin Department of Transportation primarily uses embedded pavement detectors. Embedded pavement detectors are loops of wire embedded in the pavement of each freeway lane and the on-ramps where metering is deployed. 

Detector groups are located approximately every half mile. When a large metal object passes over the loop, a measurable current is induced and sent to a roadside controller.

Speed and vehicle count data is gathered for each lane of traffic. A controller near the collection site totals the data and sends it to a local traffic operations center via fiber optic cable or leased line service.

This information provides the foundation for real-time monitoring of freeway congestion status and is used to set ramp meter timings. Travel times are calculated from this data and provided to the media and the public.