LADOT’S ADAPTIVE TRAFFIC CONTROL SYSTEM (ATCS) Presentation at the TRB Workshop on Adaptive Traffic Signal Control Systems, Sponsored by Signal Systems Committee January 9, 2000
GENERAL DESCRIPTION • PC-based real-time adaptive traffic control system • Developed by LADOT staff • Funding provided by City of Los Angeles, LACMTA and FHWA • Window NT with real-time extension • Distributed client-server architecture • Up to 400 intersections and 6400 detectors per system • Currently 237 intersections on-line • Plan to cover 2500 intersections in 3 years
BASIC PHILOSOPHY • Develop an open system to test various control algorithms • Adjust signal timing on a cycle-by-cycle basis: • Cycle Length • Splits (Critical Intersection Control) • Offset (Critical Link Control) • Each Optimizer can function independently • Maximum flexibility in section assignment • Avoid overreacting to short-term variations • Capable of responding to spikes in traffic demand
CONTROL PARAMETERS • Volume and Occupancy, collected every second, but used every cycle • Speed • Detector location • Queue length • Upper and lower limits of cycle length • Phase sequence is fixed • Minimum phase green time
DETECTOR DATA • At least one detector per phase • Detectors located 200’-300’ upstream of the intersection • Identify and screen out bad detectors • Smooth calculated demands • Project new cycle lengths • Prorate phase splits based on fixed timing plan when detector data is not available
OVERSATURATED CONDITIONS • For isolated intersections • Adapt to high occupancy data with longer cycle length • Adjust splits based on phase demands • For major arterials • Identify critical link(s) and provide progression for the congested approach(s) • Permit double cycling at minor intersections • For networks • Need further research and development
TRANSIT PRIORITY • Use loop-transponder technology to detect buses • Check bus schedule in the central database • Provide green extension/red truncation for late buses when needed • Calculate bus arrival time and determine the extension time • Minimize adverse impact on cross streets traffic
SYSTEM ARCHITECTURE • Centralized area computers (PC Server) communicate to local controllers. • Multi-port serial cards connect to communication lines. • GUI Client running on area computers and workstations. • Main Data Server provides central traffic data base and coordinates area computers.
COMMUNICATION SYSTEM • Dedicated communication path between host and local controllers • Time division multiplexing • Local controllers polled once per second at 1200 bps • Four intersections per communication line. • Multiple communication protocols • Download/Upload to local controllers
LOCAL CONTROLLERS • Type 170 controller. • BI Tran Systems 172.3 software. • Type 2070 controller. • City of L.A. Traffic Signal Control Software.
CENTRAL HARDWARE REQUIREMENTS • Rack mounted server with a backup PC. • 350 MHz PC with 192 MB RAM • Workstation with two 21-inch monitors. • Multi-port PCI serial cards. • Ethernet network.
INSTALLATION COST • Central computer hardware - $40,000 to $50,000 per system • Central software - $1,000 & LADOT license • Local controllers - $8,000-$10,000 per intersection • Loop detectors - $5,000-10,000 per intersection • Communications system - vary by types
OPERATIONS AND MAINTENANCE • Central hardware - minimal. • Central software - update costs. • Communications network - labor costs for repair.
Verej Janoyan, LADOT (213) 580-5359 e-mail:email@example.com Kang Hu, LADOT (213) 485-8523 e-mail:firstname.lastname@example.org CONTACT PERSONS