Sensors get L.A. up to speed
Traffic monitoring system compiles data from thousands of sources to deliver a detailed picture of the area's highways
NETWORK ADMINISTRATORS are accustomed to monitoring traffic to
reduce bandwidth bottlenecks. Allen Chen's task is a little
different: speeding the flow of people, not electrical impulses. As
senior transportation electrical engineer at the California
Department of Transportation (Caltrans), Chen is responsible for
managing traffic on more than 500 miles of freeways in the Los
'We are not going to build more freeways,' he said.
'But with information, we can manage them better and help
drivers make better decisions.'
In October 2007, the Los Angeles Regional Transportation
Management Center (LARTMC), a facility that houses Caltrans and the
California Highway Patrol (CHP), formally opened. There, data
assembled from more than 10,000 sensors and cameras gives operators
an overview of traffic in the area so they can act quickly to
reroute traffic or remove bottlenecks.
Although LARTMC is new, its Advanced Traffic Management System
(ATMS) represents the implementation of research that started about
40 years ago. In 1969, Caltrans began researching techniques for
improving traffic flow. Its final report, issued in 1976,
recommended four steps:
- Install a detection system to monitor traffic volume and
- Meter freeway ramps to balance capacity and demand and improve
- Use changeable message signs that inform drivers of freeway
- Provide a fleet of tow trucks to immediately remove disabled
vehicles from roadways.
'Ramp metering was very revolutionary,' Chen said.
'Freeways are designed for 1,800 vehicles per lane per hour,
but once we slow to 35 miles per hour, our throughput drops to
1,200 per hour. By maintaining proper flow with the ramp meters, we
can increase the flow up to 2,400.'
Those 1976 recommendations have been put into place, with more
than 10,000 sensors embedded in the roadways, 1,280 traffic
monitoring stations, 450 closed-circuit cameras, 960 ramp metering
systems, and 109 changeable message signs and 15 highway advisory
radio stations to keep the public informed.
In 1998, the state legislature approved funds to build a new
five-story facility to house Caltrans and CHP. Located about 10
miles from downtown, the site includes microwave and satellite
communications to CHP and Caltrans employees in the field. The
facility also is the base for a Sonet OC-12 connection to the
freeway sensors and control system.
'Using artificial intelligence, we can build filters and
algorithms that detect any anomaly,' Chen said. 'Then
the system will alert our operators, and the operators can activate
the closed-circuit TVs to investigate.'
Although Caltrans uses commercial software wherever possible
' and the systems and workstations run on Microsoft Windows
XP ' there is no commercial product designed to manage such a
traffic system. Therefore, Caltrans had to assemble software into
an overall package that met its needs. It selected Science
Applications International Corp. as the primary systems integrator
and Delcan as the chief consultant for systems architecture and
ATMS runs on Hewlett- Packard HP-UX 11i servers. Data is stored
in an Oracle 9i database ' which is migrating to Oracle 10g
' and a Gensym G2 business rules engine is used to run
scenarios and present data and suggested actions to operators. The
wall in the control room contains 12 84-inch digital light
projection displays, 12 50-inch DLP displays and two electronic
With ATMS, Caltrans is working to further reduce bottlenecks,
and it is also expanding its information outreach activities to
keep other agencies and the public informed of traffic conditions
via the Internet, radio and TV news, and cell phone/personal
digital assistant alerts.
'If the commuter knows whether it will take five minutes
or an hour to reach their destination, they can make an informed
decision,' Chen said. 'And if they decide to take a
less congested route, it will also benefit others on the