In this article, we present an overview of two key categories of
outside-the-car signal processing: intelligent transportation systems
and applications based on vehicle location systems.
Intelligent Transportation Systems
Intelligent transportation systems (ITS) are comprised of
technologies used in vehicles and roadways to manage and improve
traffic flow. A key component of ITS lies in traffic control systems,
where signal processing plays a significant role. Signal
processing-based systems are used to detect cars as they approach an
intersection, thus allowing the traffic control system to change the
state of the traffic light as needed.
One of the most common implementations of car detection uses an
inductive loop embedded under the road surface. When a car passes
overhead, the car’s metallic content alters the loop inductance, and
the car is detected. Other methods of car detection include radar,
laser, and air-filled tubes laid out onto the road surface. These
methods employ varying degrees of signal processing and analysis in
order to accurately detect vehicles.
Inductive loop detectors can also form the heart of a
photo-enforced traffic light. By using information from two loops that
are embedded in the roadway in front of a traffic light, the system can
determine when a car has passed over the loops in quick
succession—which indicates that the car is not stopping. If the light
is red when the car passes, the system can trigger a high-resolution
digital camera to take a photo of the offending vehicle.
Researchers and transit authorities have proposed many other uses for
vehicle detection technologies. For example, by placing inductive
detectors at regular intervals on highways, the current travel time
between points on the highway can be computed. This type of information
can be distributed to drivers (for example, through the Radio Data
System used in Europe or through a telephone hotline) to help reduce
congestion. Recently, such traffic information has been integrated into
select vehicle navigation systems in the U.S. through Sirius and XM
Satellite Radio broadcasts. These systems can show traffic congestion
on a map and suggest alternate routes to drivers.