At Houston TranStar, staff monitor traffic on the region’s freeways using speed-data sensors and more than 800 cameras. Photo courtesy of Houston TranStar
Every morning and evening rush hour, commuters in the Greater Houston area drive under the watchful eyes of Houston TranStar. Using about 730 pan-tilt-zoom cameras made by Sony and Cohu, staff within the agency’s vast “traffic management center” (TMC) redirect traffic using electronic overhead signs and local media, as well as dispatch police, ambulances and tow trucks when trouble occurs.
by James Careless
The time and money saved is substantial, according to A&M University’s Texas Transportation Institute (TTI). In 2009 alone, Houston TranStar’s efforts reduced motorists’ drive time by almost 11.3 million vehicle hours. TTI says, this works out to $227 million saved in fuel and related vehicle costs. In comparison, Houston TranStar’s annual budget is just $27.7 million. “So for every $1 spent on Houston TranStar, the region realizes a benefit of $9.90,” the organization says.
To monitor the nearly 400 miles of road in the Houston area, Houston TranStar uses a range of sensing devices beyond video cameras, including in-road weight sensors. “But when it comes to making traffic decisions, our people rely on video cameras first,” says David Fink, traffic manager with the Texas Department of Transportation (DOT). The Texas DOT is one of four partner agencies that run Houston TransStar. “If a sensor tells you something unexpected, it can be hard to believe. But video shows you what’s happening. You know you can count on it,” he says.
VIDEO’S MANY TRAFFIC DUTIES
Video cameras are an essential element of “Intelligent Transportation Systems” (ITS); the modern monitoring and active traffic management systems in use around the world today.
Houston TranStar’s deployment is what most people think of when they hear about traffic cameras. Those cameras collectively give TMC staff a real-time view of how traffic is flowing. Once carefully guarded by government agencies, such video is now made freely available to the media and public alike through video websites. This allows the media to tell motorists what areas to avoid, thus improving traffic flow in general, and lets drivers make those decisions before taking to the road.
The Washington State Department of Transportation has deployed high-tech message signs that deliver real-time information to drivers, and adjusts highway speeds based on traffic conditions. Photo courtesy of Washington State DOT However, video cameras play other roles in traffic management. “Video cameras are used to monitor red light infractions, and to identify and record motorists who don’t pay electronic tolls,” says Scott Belcher, president and CEO of ITS America, an advocacy group for ITS technology and operators. “Video cameras are also playing an increasing role in providing security at bridges and tunnels in the post 9/11 age.”
ADVANCES IN VIDEO APPLICATIONS
Traditionally, video cameras have served as passive eyes for TMC monitoring staff. The problem, of course, is that watching the images from 730 cameras can be boring, especially when most show that traffic is moving smoothly.
That is why many TMCs are incorporating “video analytics” into their video monitoring systems. Video analytical software takes incoming video and compares it to a set of predetermined criteria, to determine if a camera’s view deserves priority attention by humans. For instance, say a stretch of highway normally supports traffic moving at 55 mph. The video analytics software monitors the various camera inputs to ensure that traffic is indeed going that fast. If traffic has suddenly slowed down, it is likely an incident has occurred. In response, the video analytics software issues an alarm to alert the TMC operators, and puts the relevant camera views up on one of their main screens.
In Seattle, a combination of roadside cameras and video analytics provide motorists with detailed feedback on real-time lane speed on the I-5 highway. “This stretch of road brings commuters to and from Boeing, so it is usually packed during rush hours,” Belcher says.
‘Safe Clear,’ a quick-clear tow program, safely removed more than 59,000 stalled vehicles along Houston’s highways during 2010, saving millions of dollars in lost time to area motorists. Photo courtesy of Houston TranStar Under the Washington State DOT’s I-5 “Active Traffic Management Project” (WSDOT I-5 ATMP), electronic information signs are placed above each lane. The cameras and road sensors work together to tell motorists the actual vehicle speeds occurring in each lane. The information allows them to slow down early, to prevent stop-and-go driving.
CHALLENGES AND RESPONSES
Keeping a network of remote controlled video cameras deployed along hundreds of miles of roadway is no easy feat. Just coping with normal wear-andtear is a challenge for Houston TranStar. “Typically, about 90 percent of our cameras are operational at any given time, which means we have people out on the road fixing the other 10 percent,” Fink says. “CCD chips lose resolution from constant exposure to daylight, pan-tilt-zoom motors wear out, and weather takes its toll,” he says.
Mindful of those problems, Axis Communications has equipped its internet-protocol (IP) based video cameras with thermostat-controlled motor heaters. “Starting up servo motors in subfreezing temperature wears them out sooner,” says John Bartolac, Axis’ manager of government programs and government business development. “To prevent this damage, our thermostats stop the motors from operating until the interior camera housing has become warm enough.”
Technological change is another issue faced by TMCs. For instance, Houston TranStar runs on fiber optics using the “Asynchronous Transfer Mode” (ATM) network standard. “The trouble is that ATM is no longer supported by manufacturers, who are all moving to IP,” Fink says. “As a result, we are having to convert our ATM network to IP.”
The good news from that is the increasing broadband speed offered by commercial cellular networks are allowing many TMCs to deploy wireless cameras instead of wired. Such cameras are much quicker and cheaper to deploy, and they allow operators such as Houston TranStar to expand their coverage.
Finally, there is the human factors that affect video traffic surveillance; namely vandalism and tight government budgets. The first problem is driven by thieves stealing network cables—whether they are copper or not—to sell them to metal recyclers. The second challenge is a matter of decreasing tax revenues due to the recession. “When money is tight, politicians look for places to cut back, and traffic management is a prime target,” Belcher says. Typically, it is the maintenance budgets that get hit hardest putting the future of their traffic management systems at risk, he said.
Today’s traffic management systems are beginning to use video to make software-defined decisions, using video analytics programs to “decide” what is being seen on camera and how it should be responded to. As computer and software capabilities increase, it seems likely that more of these decisions will be diverted over to machines, rather than human operators. Properly executed, that should result in better traffic flows, and the freeing of human monitors to deal with truly complex situations.
Add IP-based cameras that interface directly to government local area networks (LAN) and wireless video transmission to TMCs, and the possibilities are impressive. Those trends will likely produce video-based traffic management systems that will be simpler and easier to deploy, placing them within reach of smaller jurisdictions with small budgets.