Wireless Traffic Management System 1
Introduction The County of Los Angeles Department of Public Works (LADPW) manages surface street traffic flow in one of the world s largest metropolitan areas. The county is composed of 37 incorporated cities comprising an area of 4,060 square miles with population of 9.9 million. Surface streets in the county feed 12 million cars to freeways for the daily commute. The commute time by drivers, including traversing surface streets, averages 30 minutes for residents of the county. The volume of traffic and rising commute times spurred LADPW to develop a wireless communication network to serve as the foundation for a multijurisdictional Intelligent Transportation System (ITS). To control and coordinate 932 signalized intersections in Los Angeles County, LADPW sought a wireless network solution to provide high bandwidth for their ITS, that would utilize existing public traffic lights, light poles and other public buildings for equipment installation and that would be affordable on a recurring cost basis. Using such a wireless network, LADPW staff could remotely monitor traffic conditions through roadway sensors and closed circuit television cameras at their Traffic Management Center in Alhambra, California and control traffic signals based on the sensor and CCTV data. They could also be notified immediately of malfunctioning traffic signals and deploy maintenance crews expediently. The grid pattern of traffic intersections and relatively flat topography in LADPW s selected area is an excellent fit for wireless broadband communications. Unwiring intersection-tointersection connections eliminates monthly leasing costs from third-party communication providers and supports implementation with zero down time of existing traffic controller equipment at each intersection. The wireless network could also support future projects providing real-time information to motorists on traffic conditions with automatic re-routing advisements, changeable message signs, highway advisory radio and Internet access for traffic-only web sites. Additionally, the communication network could facilitate high-speed information flowing in and out of the County-designed Information Exchange Network (IEN). This intersection traffic control network connects multiple agencies and cities within LA County to share real-time information on traffic intersections and major arterial roadways. The system has allowed for improved response and congestion management to special events or incidents along freeway or surface streets between the cities. First Phase: 51 Intersections In 2006, LADPW awarded Systems Integrated, LLC, a contract to wirelessly network 51 signalized intersections. Requirements for the first implementation were twofold: provide 2
a network facilitating high speed communication between the Traffic Management Center (TMC) and intersection controllers and CCTV cameras installed at select intersections; and convert serial based communications from the County s Kimley-Horn Integrated Transportation System (KITS) communication server into TCP/IP packets compatible with the wireless network topology and back to serial formatting at the traffic intersection controller. Each intersection site consists of an Advanced Transportation Controller (ATC) mounted street-side inside a secure cabinet. The TMC houses a KITS communication server providing the capacity to communicate once per second with up to 256 intersections. Four intersections were selected to host IP-based pan-tilt-zoom (PTZ) cameras. The wireless network was required to provide segregated, guaranteed throughput of 512 kbps at each intersection to allow the TMC to remotely monitor each camera using full-motion video at 25 frames per second while simultaneously sending PTZ commands to control the cameras. Systems Integrated first undertook a wireless survey of the 51 intersections to determine the best solution while considering several factors: a. The completed wireless communications network would allow one second polling of 51 traffic signals and 4 cameras. The conceptual design stipulated two radio networks, one for video and one for traffic signal management. b. LADPW would providet1 circuits to backhaul traffic controller data and video to the TMC with a maximum of 8 intersections per T1. c. Base Station Master Radios were to be concentrated in a minimum of locations and preferably mounted at public facilities to facilitate connection to a T1 line from the local phone company. d. Custom software interfaces were required to communicate with ATC traffic controllers in 332 controller cabinets. e. The wireless equipment should incorporate the latest developments in the field of wireless data transfer and security. Given guidance from LADPW to minimize recurring costs, especially T1 costs, Systems Integrated created a network blueprint that met all performance requirements while simplifying the conceptual design. Key to satisfying the requirements stated by LADPW was deploying a Proxim Tsunami MP.11 5054-R point-to-mulitpoint wireless system. The Tsunami product line met all requirements for data transmission rates, security using Proxim s Wireless Outdoor Routing Protocol (WORP) to prevent snooping or intrusion, ease of deployment, field configurability as well as Web and SNMP-based network management. 3
Solution Components Radio Network Using the high performance Proxim Tsunami MP.11 5054-R product line allowed Systems Integrated to simply the conceptual network design by deploying a single communication network for supporting traffic signal management and video data requirements. Proxim s VLAN support enabled the two types of data traffic controller communications that created small packet traffic and video stream data in larger more bandwidth intensive packets to be segregated into their own network spaces. The MP.11 5054-R also supports quality of service (QoS), enabling each type of data traffic to receive the necessary bandwidth and latency to meet LADPW performance requirements. Typical Radio Installation The Systems Integrated engineering staff analyzed the coverage area and performance requirements and determined a single T1 could meet all data and video requirements. The T1 was installed at Hawthorne City Hall and a head-end radio installed to connect into the Proxim network. Project intersections were categorized into sequential intersections that did not branch off laterally, and intersections that had one or more north-south and eastwest components. Intersections requiring communication down multiple north-south or east-west corridors were outfitted with two Tsunami MP.11 5054-R Base Station Units and either omni or ector antennas to service each direction. Intersections that were on a single north/south or east/west monitored corridor were outfitted with a Tsunami MP.11 5054-R Subscriber Unit and an internal antenna oriented toward the nearest Base Station intersection. 4
Starting at the end of a length of intersections, four to six Subscriber Units were oriented towards a base unit with an omni antenna. The chain of intersections could continue on the other side of the base unit for the same number of intersections. When a lateral street of intersections was encountered, a Tsunami MP.11 5054-R Base Station was mounted on a light pole at 90 off from the previous direction to service the row of intersections. If only one direction was required (e.g. from North to West only), a 60 sector antenna would be used. SYSTEM FUNCTIONAL BLOCK DIAGRAM Traffic Controller Interface Interfacing to the ATC located at signalized intersections required that packetized data transmitted over the wireless network convert to serial based communications compatible with the ATC CPU. LADWP also specified that space use inside the controller cabinet be minimal. Systems Integrated s electrical engineering group designed a card that fit in the ATC cabinet to provide Ethernet to serial conversion of data. Additional components inside the cabinet include power cubes providing Power over Ethernet (PoE) to traffic signal mast mounted radios and a 5-port Ethernet switch to 5
connect radios, the Ethernet-to-serial converter and future IP devices needed at the intersection. These components provided the pathway through which polling commands originating from the TMC and the KITS are disassembled into serial protocol for use by the ATC. Replies from the serial communication interface are reassembled into packets and transmitted out the radio interface for delivery to the TMC and KITS. Traffic Management Center/KITS KITS uses serial communications to poll each LA County Traffic Controller (LATC) once a second. The original system consisted of multiple LATCs connected to a single serial port through copper wiring installed at each intersection. This scheme allowed KITS to communicate with up to 64 LATCs through one serial communications port. Systems Intregated s engineering staff analyzed the KITS protocol and the LADWP s requirement for once per second updates from each LATC and determined a communication processor would be necessary to meet the timing and throughput requirements. The Wireless Communication Server (WCS) is a Windows server and two Digi- 6
board 16-channel serial multiplexers. The WCS is connected to the KITS I/O server. The WCS maximizes polling capabilities of a TCP/IP based network communicating with the serial-based ATCs located at each intersection. Systems Integrated developed the polling software to operate within tight limitations of the KITS protocol and the requirement to eventually support 900+ intersections. This design allows the TMC KITS server to run unaltered, polling intersections through its serial ports. The WCS immediately responds to the polls using cached data from its latest query through the wireless network. Based on calculations of data latency and the number of LATC s the WCS can communication on each of the 32 serial channels, the communications transport system will support more than 1,200 LATCs. While the wireless network has sufficient bandwidth, other limiting factors such as the backhaul T1 speed cap the system s performance. Video Surveillance At the time this paper was written, the four PTZ cameras were yet to be installed. As part of system performance testing, a traffic detection camera was installed to validate the wireless network s capacity to support video feeds from the remote intersection into the TMC. Analysis of the video stream data and quality confirmed that the density of cameras needed for the 51 intersections would be supported using a constant three frames/sec capture rate. Future Plans Systems Integrated s industry and engineering experience provided a solution that met the varying technical challenges of LADPW s Traffic Management System. The LADPW system uses Proxim s Tsunami MP.11 to create a high throughput, robust and cost effective wireless backbone upon which multiple remote applications can be monitored and controlled. The successful deployment of the wireless network, a common ATC interface, and integration with the TMC s KITS server for the initial 51 intersections within budget and on time has resulted in a second contract for the Systems Integrated and Proxim team to expand deployment to 900+ intersections. This system, when completed in late 2009, will make the LADPW TMS network one of largest of its kind in the U.S. 7
Background Systems Integrated LLC, a privately owned company founded in 1974 has provided unique engineering solutions to companies worldwide. SI designs, assembles, and implements wireless solutions for a wide variety of applications and market segments. Since the advent of 9600 baud licensed wireless communications, SI has utilized this medium as a way to free their customers from the limitations and expense of wired alternatives. Initially providing wireless services to both government agencies and private industries, SI found much success implementing wireless solutions for the Water, Wastewater, Hydropower, Telephone, Oil & Gas and Electrical Distribution markets. Today, SI has expanded their customer base to include many commercial business sites in need of wireless solutions. Information about Systems Integrated and their solutions can be found at: www.systemsintegrated.com. Proxim Wireless Corporation (NASDAQ: PRXM) is a leader in core-to-client solutions for broadband municipal wireless networks. Our systems enable a variety of wireless applications including security and surveillance systems, mobile workforce automation and machine-to-machine communications. We have shipped more than 1.5 million wireless devices to more than 200,000 customers worldwide. Proxim is ISO-9001 certified. Information about Proxim can be found at 8