T-rex Comes to Life
Imagine...sitting in an Internet cafe checking the traffic conditions for your route home.
Introduction
Imagine commuters sitting in the local Internet café and checking the traffic conditions for their route home. As the traffic engineer sitting at the next table, imagine checking your traffic management system for the overall traffic conditions in the metro area. Now imagine checking the status of each and every sensor in your traffic system? Sound unfeasible? Read on.
On the other end of this cafés Internet connection is a smorgasbord of communication links from the traffic management center (TMC) to the traffic sensors. Getting to your Autoscope wide-area video detection system can be accomplished today by virtually any communication system devised, except perhaps two cans and a string!
Image Sensing Systems offers traffic video detection systems in two basic configurations: the Autoscope Solo Pro, an integrated sensor with camera and video image processor in one compact housing, for customers who prefer the integrated solution; and the Autoscope RackVision product family standalone image processors, for those who prefer a separate camera from the processor or who require processing systems for cameras already in place.
You could always communicate with your field sensors via traditional RS-232/422/485-based serial connections. The possibilities include private or public twisted pair copper wiring, phone modems, fiber optic infrastructures, and many wireless options. Making traffic management more effective demands more information from greater numbers of sensors in the field. That means faster transmission rates and more flexible communication options that support rapid, low cost deployments. In the past few years, an explosive growth in equipment, software, and IP-based communications infrastructure is bringing more computer networking capabilities not just to the TMC but to traffic cabinets in the field.
Faster Communications?
You can think of the communications link as a pipeline between the TMC and the equipment in the field. The size of the pipe affects how much data can pass. For each communications task, the amount of data waiting to enter the pipe thus determines how long the transmission will take. Imagine pushing 60 gallons of water through a garden hose or through a fire hose—the fire hose will get the job done sooner!
Flexible Communications
IP-based communications were once the private domain of sophisticated computer networks, but that’s changing fast! The IP-based Autoscope vehicle detection system supports the trend to deploy this networking capability into TMC-to-field communications. Important traffic data collection, limited until recently by the cost of expensive equipment to reach only major traffic corridors, can now come from low-cost remote video sensors using only solar power!
The Autoscope communications software has embraced IP-based communications since 1996. The first implementations allowed applications software running on Windows or UNIX platforms to communicate with a Windows-based Autoscope communications server over a LAN or WAN.
At that time, vendors such as Digi International and Comtrol Corporation offered terminal servers to extend Ethernet links from the TMC to environmentally-controlled hub buildings in the field. These products provide as many as 64 traditional RS-232/422 serial ports to connect to field equipment. These vendors also provide terminal server device drivers that make it look to software as though the remote serial port is actually a serial port on the PC. These device drivers perform a valuable service, as they permit serial communications without modifying legacy software.
While not the norm for most installations, use of these systems grew throughout the 1990s. Recently these vendors introduced small, single-channel ’Ethernet-to-serial’ adapters—essentially single channel terminal servers—suitable for the harsh traffic environments of a roadside cabinet. Figure 1 shows several examples of these adapters.
During this same time, terminal server and other communications electronics have increased the data transmission rate by more than a factor of twelve. In the early 1990s, most traffic equipment was limited to 1200 baud or perhaps 9600 baud. By the late 1990s, some traffic equipment was supporting 115,200 baud and even 230,400 baud. Using the pipe analogy above, this is like increasing the garden hose to a 6-inch gusher!
TCP/IP Comes of Age
In 2001, an Autoscope communications software enhancement eliminated the need for the device driver by creating a tunnel directly through a TCP/IP socket channel to IP-based devices in the field. By simplifying the setup and by optimizing use of these channels, the Autoscope system achieved a three-fold increase in data throughput. Again using the pipe analogy above, this is like reducing the 60 gallons of data to 20 to get the same task done.
Since this capability was introduced, we have experienced a significant growth in the number of projects using TCP/IP links to the field. IP-based communications equipment ranges in speed from the slow to very fast, including cellular modems, fiber optic transceivers, and wireless radios. IP-based technology can serve the purpose regardless of the size of the pipe! Cities and counties are adopting visionary strategies to bring IP-based communications to traffic cabinets and to remote data collection stations. The enhanced information gathered, including real-time traffic data, alarms, and camera video will serve customary traffic management functions, support emergency evacuation plans, and increase homeland security.
One such unique project, distinguished by its rapid deployment and size (and hence its name) is the T-REX Project in metro Denver, Colorado, USA.
The Project
Southeast Corridor Constructors (SECC) is a joint venture of the Kiewit Construction Co. and Parsons Transportation Group and includes DMJM-HARRIS, HNTB Corporation, Turner Collie & Braden, Sverdrup Civil, Inc. and Kleinfelder, Inc. A number of firms serve as subcontractors and suppliers, such as Mass. Electric Co., Sturgeon Electric Company, Inc. American Civil Constructors, Dynalectric Company of Colorado and Anko Metal Services, Schnabel Foundation Company, Jalisco International, Inc., and Penhall Company. Numerous suppliers provide equipment and services, including Econolite Control Products, Inc. and Image Sensing Systems, Inc. with the Autoscope wide area video detection system.
T-rex
The Transportation Expansion, or T-REX, project in the southeast metro Denver area in Colorado will improve and expand highway and transit capacity. Approved by voters statewide, the $1.67 billion project includes highway widening, bridge and interchange improvements along 17 miles of I-25 and I-225, and a 19-mile extension of the region’s light-rail transit system. The project area is shown in Figure 2. The T-REX project is a collaborative effort by the Colorado Department of Transportation (CDOT), the Regional Transportation District (RTD), and the U.S. Department of Transportation (FHWA and FTA), along with numerous city, county and regional agencies.
In an innovative approach to project management, a design-build concept, combining the design and construction phases into a single contract with one contractor, is speeding this massive project to completion. In June 2001, a $1.186B design-build contract was awarded to Southeast Corridor Constructors (SECC) to complete the designs and construct highway and light rail improvements in the southeast metro Denver area by the end of 2006.
To meet the T-REX project completion deadline of 2006, 22 months ahead of the original schedule, SECC set an early goal to establish an interim traffic management center with appropriate ITS technologies deployed in the field. This would support a creative public information plan to help motorists select the best routes and also speed coordinated responses to incidents. A primary goal of T-REX is to minimize inconveniences to the public.
The Autoscope portion of this massive project involves over 300 Autoscope Solo® Pro sensors for traffic monitoring on arterials surrounding the construction area. Traffic on these arterials has increased substantially due to diversion from the freeways as construction progresses from site to site. The increased congestion on the freeways encourages people to choose alternate arterial routes instead of struggling along a congested freeway. Each Solo Pro sensor measures traffic mid-block along these arterials.
Detection and communication
A key project goal was rapid deployment of ITS technology, including the Autoscope wide area vehicle detection system. The schedule and budget did not allow extensive trenching and installation of power and communications lines along arterial streets. It was decided early in the project to use solar power where necessary (at 25 per cent of sensor sites), and to use the cellular phone network (at 100 per cent of sensor sites) for data transmission back to the TMC.
The Autoscope Solo Pro sensors use very little power, making them ideal for solar powered installations (one sensor consumes only 15 W maximum when the faceplate heater is on). Each sensor can be powered by a 12-to-24 VDC solar array or 24 VAC when connected to the power grid.
For communications to the TMC, the Solo Pro sensor connects directly to a rugged AirLink Raven II, full-duplex cellular digital packet data (CDPD) modem, shown in Figure 3. The cellular service is provided by AT&T Wireless with a private line to the TMC. However, during initial installation of sensors, secure communications over the Internet allowed technical staff to access sensor sites from various locations throughout the USA.
Cellular digital packet data, sometimes called ’wireless IP‘, is based on the same TCP/IP protocols that drive the Internet. The CDPD modem sends information over the air in packets of data at a rate of up to 19.2 kbps. Actual throughput will typically be 10 to 14 kbps. As today’s communications systems go, this is a rather small pipe! However, the benefits of quick, easy installation and savings over trenching conduit are significant. The CDPD modem facilitates temporary installations for maintenance, monitoring or education and permanent installation for traffic management or telematic applications. The design engineer must consider the tradeoffs between the amounts of data required versus the speed of transmission available.
Each CDPD modem is configured with a unique IP address and port number. At the TMC, a corresponding communications channel is defined for that IP address and port. A few of the 300 IP-based cellular channels are shown on the left side of Figure 4, while the corresponding Autoscope Solo Pro sensor description is shown on the right. The CDPD modem uses a 128-bit encryption protocol for very secure data transmission.
A typical camera field-of-view and detector layout is shown in Figure 5. Note that the long mid-block detection area calls for an unusual camera orientation: the camera is rotated to zoom in on the traffic while still seeing the farthest away detection station. This ability to zoom in allows optimal detection over a wide area at each site.
Figure 6 shows a plan drawing of the detection zones relative to the nearest intersection. Each Autoscope Solo Pro sensor measures volume, occupancy, and speed at four stations, each about 90 feet apart within the field of view. At the closest detection zones to the sensor, traffic data is collected for each lane. In the farther away stations, representative data is collected in only the center lane. In addition, each station detects a stopped vehicle, signifying a queue backup from the intersection.
Each Solo Pro sensor accumulates the traffic data into 20-second time intervals for transmission to the TMC when requested via the Autoscope Comserver. Periodically, video snapshots of traffic are also sent to the TMC. These snapshots assist in maintaining the detection system and can also be posted on the T-REX web site (see Figure 7).
Integration
SECC defined the vehicle detection data required for the arterial monitoring system as shown previously in Figure 6. Working with Econolite, they determined what detectors and naming conventions to use within the Autoscope Solo Pro sensors. As the sensors and CDPD modems came on line, Econolite personnel programmed the sensors with the requisite detection zones. Since these sensors are accessed via the Internet, setup and any consequent troubleshooting during integration could be (and was) performed from any location with Internet access!
The SECC software team was very good at notifying the rest of the integration team when problems occurred. They provided timely, helpful information to replicate and fix problems found. Integration is never an easy task and with the large size, high visibility and project deadline, the SECC team aptly applied the design-build philosophy of the overall T-REX project to diligently pursue and resolve every issue.
Early on, the team found it advantageous to divide the installed equipment into two virtual networks and run two comservers during the integration period. One comserver used the most recent stable software to test for continuous data polling and snapshot retrieval over a long period of time, while the second comserver used the ongoing latest build of software to address recently found issues. As sensors came on line, they were added to the secondary comserver first.
While a number of hardware installation and software problems were identified and rapidly fixed throughout the integration period, a certain class of problems posed a significant challenge to overcome. These issues related to the latency in communications over a large CDPD cellular network. While the data packet delays or latency were typically below 10 sec, and occasionally over 10 sec, these delays were still orders of magnitude larger than delays typically experienced over wire line, fiber, phone modem or even wireless radio communications. Software tools were built to log the raw data packets sent and received by the comserver with timestamps and to automatically extract the latency. These and other software tools were instrumental to identify and compensate for these long delays.
Generating public information
The SECC software development team used the Autoscope Comserver Software Developer’s Kit (SDK) to integrate sensor data into the T-REX traffic management system applications software. The SDK provides the header and include files necessary to build a client application that interacts with the Autoscope Comserver. Responding to polling commands from this client application, the Comserver retrieves traffic data and video snapshots from the Autoscope Solo Pro sensors over the CDPD link.
The applications program interprets the traffic data and stopped vehicle alarms to grade each approach for smooth traffic flow. Like a traffic signal, each approach to the intersection is assigned a RED, YELLOW or GREEN grade for its current level of congestion. This information and the latest video snapshots are transferred to a public web site available to news organizations and the traveling public. The web portal to access this live traffic information is shown in Figure 8 and can be accessed via www.trexproject.com.
Conclusions
The low power consumption of the Autoscope Solo Pro video detection system is ideal for rapid and low cost deployment of vehicle detection using solar power and wireless communication devices. The recently introduced capability to tunnel through TCP/IP Socket channels to IP-based communication equipment and Autoscope sensors supports the design trend of bringing Ethernet connections to field cabinets. This ensures our customers a solution that meets both their detection objectives and their communication requirements for data and video.
The T-REX project in the metro Denver area is an excellent example of IP-based communications to field devices, offering much convenience in the setup and maintenance of traffic sensors. The shear size and design-build culture of the T-REX project spawned innovative, breakthrough solutions to meet their traffic monitoring goals.
You might not go to your local Internet café to inspect your traffic management system and sensors. But isn’t it nice to know you can? At the very least, this technology can save you from that drive to the office on your day off—you can check your system from home just as well.
Authors
Craig Anderson, Image Sensing Systems, Inc. and Dave Candey Jr., Econolite Control Products, Inc.As published in Traffic Technolgoy Internation Annual Review 2003
©2003 Traffic Technology International
