Fiber in Action

State Department of Transportation uses video multiplexers to monitor traffic

Don Vondran, ITS Implementation Engineer for the Washington State Department of Transportation, discusses using video multiplexers to monitor traffic in the greater Seattle area.

Mr. Vondran, a Licensed Professional Engineer in Civil Engineering, has worked at the Washington State Department of Transportation (WSDOT) for 10 years. In 1997 he began working in the Intelligent Transportation Systems Operations group, learning how the different ITS devices worked and how they were used. Today, he handles the operations of the existing ITS system as well as researching new devices.

The WSDOT ITS system consists of 250 cameras, 120 ramp meters, 175 vehicle data accumulation stations and 55 variable message signs, as well as a fiber optic backbone that carries all the video and data. Multiplexers are used to convert standard analog video from the cameras, into a high-speed, serial digital bit stream for transmission over fiber optic cable to the Traffic System Management Center (TSMC). The information that is gathered at the TSMC from the cameras and data stations is disseminated to the public in various forms. On the freeway there are variable message signs (VMS) and highway advisory radio (HAR) signs that give motorists information about accidents, congestion and construction. Real-time traffic information is provided via the telephone (1-800-695-ROAD) as well as the internet (http://www.wsdot.wa.gov/pugetsoundtraffic/cameras/). This allows motorists to plan their trips based on current traffic conditions.

On a daily basis, Vondran reviews trouble reports received from operators within the TSMC about ITS devices that are not functioning properly. He then troubleshoots to determine what is causing the problem and either fixes the problem or determines what means are necessary to resolve it. This sometimes involves replacing or upgrading existing equipment or researching new cost effective ways to accomplish the same end result. He also works with contractors on the installation of new devices and provides technical assistance.

In 2000, while searching the Internet for some information about some existing multiplex equipment, Vondran came across the DeciMux™ by Communications Specialties. “It was not what I was looking for at the time but it did capture my attention,” explained Vondran. “I printed out a specification sheet and later discussed it with Greg Leege, another ITS Implementation Engineer, and others within TSMC. The primary attraction was what it accomplished in a very small size. The method we were using then involved multiplexing the video and sending it to the TSMC via three different pieces of equipment. The first piece was an analog modulator shelf, from there all the modulated signals went through a combiner and finally to a transmitter. At the TSMC we would reverse the process and begin with the receiver, on to a splitter and then to a demodulator shelf.

“Over the years our system had grown and our equipment room was very full. We realized that the DeciMux could accomplish the same process in a one rack unit high piece of equipment. This took up at least 5 times less space! So, we figured that it would be worth finding out how much it cost. We were paying about $3500-$4000 per channel of video that we sent back to the TSMC. I found out that the DeciMux came out to $1000 per channel. We had not seen any other units that could accomplish what it was doing for the size and price. So, with the knowledge that we needed space for future projects that would be installing more equipment, we felt it was worth getting a demo and trying it out.“
“When we received our DeciMux demo we needed to determine where we wanted to test it out. We currently have 13 Hub locations that we bring video back from. These Hubs primarily consist of steel controlled environment vaults (SCEV) that are placed underground. They are in a room about 10’ x 10’ square. They act as collection points for data and video and then at each Hub we multiplex the video and send it to the TSMC. This allows us to get more bandwidth from each individual fiber so we do not waste an individual fiber for each camera. For example, the DeciMux combines (muxes) 10 (deci) video channels onto one strand of fiber. Our Hubs are anywhere from 10 to 35 miles away from the TSMC. So, we determined that the best way to test it out it was to install it in the Hub that was 35 miles away. We installed the DeciMux in the existing 19” rack and plugged in the coax from each individual camera and then plugged in the fiber. We did the same thing at TSMC (receiver end). The process was very quick and easy and the video looked great. There has been little to no training necessary and there have been virtually no problems with the units.”

“What was nice about the DeciMux is that it processes the video digitally. This means that there is no tuning or adjusting needed. With our old system being analog we would have to have our maintenance technicians tune our equipment periodically. Over time the video from one camera would “bleed” onto the other or you would begin to get some deterioration of the video signal. With the digital video there is no problem with channels bleeding.”

The WSDOT has been very happy with how the DeciMux performed. Since the initial installation, they have incorporated the multiplexer into new projects and now have almost 25 systems installed.

Communications Specialties now offers a digital, 10-channel multiplexer with optional bi-directional data (RS-232, RS-422, RS-485). For more information on the Pure Digital Fiberlink® 10-Channel Video Multiplexer/PTZ visit www.commspecial.com.

 
Manufacturer of Fiberlink, Scan Do & Deuce