Vehicle Detector Stations (VDS)
Vehicle detector stations are the major elements of practically all freeway traffic management systems. Inductance loops are the most widely used detectors in freeway traffic management systems because of their reliability in data measurements and flexibility in design.
The main function of VDS is to detect the passage and presence of vehicles on the freeway. Data
collected at vehicle detector stations is initially processed by a micro processor (Advanced Traffic Controller) located at the side of the highway. The processed data contains traffic volumes, vehicle speeds, occupancy, and vehicle length information.
This information is then transmitted at regular polling intervals to the Central Computer System located at the Traffic Operations Centre via the communications subsystem. The computer system will use the data to monitor traffic patterns and identify
traffic incidents as they occur.
An inductance loop detector system basically consists of three components:
a loop embedded in the pavement consisting of multiple turns of wire; - a lead-in cable which connects the loop wire to the input of the loop detector amplifier;
- a detector amplifier that intensifies the electrical energy produced by the detector loop.
The loop detector shape may vary depending on its requirements:
diamond shaped loops are used in multiple-lane mainline sections because they are less likely
to pick up vehicles on adjacent lanes; - rectangular shaped loops are used in freeway ramps where only one travel lane exists. The wide detection zone ensures detection of vehicles around the curves.
Vehicle detector stations that have a double-loop arrangement are specifically designed to measured vehicle speeds and lengths in addition to the traffic volumes and occupancy information. Stations with one loop per lane are capable of directly measuring traffic volumes and occupancy information only.
See also:
- Traffic Operations Centre (TOC)
- Central Computer System
- Closed Circuit Television (CCTV)
- Vehicle Detector Stations (VDS)
- Changeable Message Signs (CMS)
- Ramp Metering Stations (RMS)
- Field Provisions (ducts, cabinets, footings, power, etc.)
- Communications Subsystems:
