Introduction
Techniques for controlling traffic have been in use ever since the automobile became the standard mode of transportation in the early 1900's. Perhaps the most familiar example is the stoplight, which in its most basic form uses a simple timer to determine when the light will change. The timed traffic light poses a problem for low-traffic intersections, since cars may need to wait at a red light for an extended period of time, even when there are no cars driving by on the cross street. This problem is usually solved by embedding a simple inductor-type automobile sensor just under the surface of the pavement. Controlling high-traffic intersections is more complicated, and is best handled using algorithms that depend on the number of cars coming from all directions at any given time, or using human operators to switch the lights based on a visual observation of the number of cars waiting at the intersection.
In addition to traffic lights, other
sensors and traffic related devices commonly used include
cameras, roadside LED displays, street lights, parking
lot entrances, and even parking meters. What has been missing
until recently is an easy and economical way to monitor
and control the devices located in a given area, such as
at an intersection or a self service parking lot. MOXA's
UC-7420, a miniature front-end computer with eight RS-232/422/485
serial ports, dual Ethernet ports, PCMCIA card that supports
802.11b/g wireless LAN capability, and an industrial strength
no fan, no hard drive design, is ideal for these kinds
of applications. The UC-7420's built-in Linux operating
system makes it easy to install software, and the CompactFlash
expansion slot lets users add additional memory space as
needed.
Traffic Control at Busy Intersections
At busy intersections, IP cameras
can be used to allow human operators to gage the number
of cars waiting at the intersection. The UC-7420 transmits
the images over the Internet from the intersection
to a remote monitoring center. Signals that control
the status of each traffic light can also be transmitted
from the UC-7420 to the monitoring center. For this
type of application, the human operators use their
traffic
control experience to determine the best time to change
the light from red to green to alleviate snarled traffic
conditions. The strategy of placing a combination of
IP cameras and front-end embedded computers at busy
intersections around a large city can be used to create
a city-wide traffic control system. Roadside LED displays
can also be used to issue traffic warnings to motorists
to avoid the most congested areas of the city.
Controlling Traffic at an Automated Parking Lot
We've all had the experience of entering a large parking lot, only to drive aimlessly around the lot for several minutes before locating an available space. A combination of sensors and LED displays can be used to create an effective traffic control system that directs motorists from the entrance to the nearest empty parking space.
One option is to use sensors that automatically
detect which parking spaces are occupied and which spaces
are
empty. The sensors can be connected to a UC-7420 through
a local RS-485 network. The UC can be programmed to monitor
the sensors continuously, and when a car leaves a space,
this information is relayed to a central computer over
an Ethernet LAN, or 802.11 wireless LAN. The UC-7420 can
also be used to connect the LED displays to a central computer.
The central computer monitors the information from all
of the sensors in the parking lot, and when a car enters
the parking lot, it uses the LED displays to direct the
driver to the nearest empty space.
Benefits
- No fan, no hard drive design for longer MTBF
- CompactFlash slot
for adding gigabytes of storage space
- Multiple connection options for greater networking versatility
- Programmability gives system integrators infinite possibilities
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