Machine Vision for Intelligent Traffic Systems
Today’s high volume of traffic on our roads is being more and more assisted by Intelligent Traffic Systems.
Things like identifying traffic violations, detecting objects on the highways, general traffic monitoring and efficient toll collection, all help to keep our roads moving and more importantly safe!
- Enforcement – Enforcement systems are used to detect a range of offences such as speeding, red light infringement and lane violation. The goal of these systems is to change driver behaviour and make roads safer. Cameras for these applications are typically based on high sensitivity sensors starting from 2MP at 25fps or more.
- Toll Collection – Cameras are used to read number plates of vehicles passing through toll gates and then electronically deduct toll fees from the account associated with each plate. The major advantage of this process is that Electronic Toll Collection can be done on moving vehicles, making it very quick and efficient compared with vehicle stopping to pay tolls. Another common toll enforcement application is where cameras are used to identify the size of a vehicle so that an appropriate toll rate can be paid or prevent fraud by capturing licence plates of non-paying vehicles.
- Traffic Monitoring – Cameras help monitor traffic flow, as well as road and weather conditions. A very important application is Automatic Incident Detection to ensure quick response to accidents and other obstructions. This is particularly useful in critical locations like tunnels and bridges. Cameras used in traffic monitoring must handle difficult weather conditions and changing lighting. Things like retractable IR-cut filters and automatic iris control enable highly flexible adaptation during day and night hours. In combination with a wide dynamic range and high sensitivity these features ensure excellent image quality under tough environmental conditions.
Key camera features for Intelligent Traffic Systems.
- Real time capability: Image capture needs to start immediately after a trigger signal has been sent to the camera. This is especially important in high-speed applications such as speed enforcement, tolling and for any flash synchronisation.
- Sequencer acquisition mode: It is typical to set up cameras to capture a series of sequential images in very quick concession with different settings such as varying exposure times. This is very useful when the camera needs to capture a highly reflective car license plate and the driver’s face at the same time with very different brightness levels
- Broad sensor range: ITS applications require a wide range of sensors to accommodate different price points, resolutions, frame-rates, technologies (CCD/CMOS), and pixel sizes.
- High sensitivity: The camera sensor sensitivity is often critical, allowing for short exposure times to capture clear images of fast-moving objects, (e.g. in speed enforcement).
- Auto iris functionality: Historically, lenses with auto iris functionality were essential, but newer high dynamic range sensors can now be used in combination with automatic gain and exposure control for different light conditions.
- Day/night functionality: Cameras with day/night functionality is essential. Historically these were equipped with a movable IR-cut filter placed in front of the sensor in good light conditions and removed to make use of infrared light for clear black-and-white images in low light.
- Dual bandpass filtering: It is now possible to use a modern dual bandpass IR cut filter with a narrowband pass window in the IR at 850nm or 940nm in combination with a colour camera. This can produce comparable performance to older day/night cameras but with much higher resolution.
