TTI cabinet installed adjacent to City of College Station traffic cabinet
Equipment at the site
George Bush Drive at Wellborn Road hosts the largest deployment of TTI equipment within the corridor. A full field cabinet was installed next to the City of College Station traffic signal cabinet. The TTI cabinet houses all the video equipment and field computers required to support any computational needs in the field. The cabinet is the connection point for the single mode fiber and holds the fiber optic communication gear.
View from pan / tilt / zoom camera on soutwest pole
There are two pan / tilt / zoom cameras located on the northwest and southwest side of the intersection. The cameras enable full monitoring of traffic AND rail for any research need. The video is digitized and compressed before being sent back to the TransLink TMC via single mode fiber. These cameras are providing the motion video seen elsewhere within the web pages and as live traffic cams into the TMC.
TTI staff installing the pan / tilt / zoom camera on the southwest traffic signal pole
Rail detection is accomplished with a pair of doppler radar sensors. A Whelen wide band doppler radar sensor measures the speed of passing trains but, being wide angle, is unable to "pinpoint" the location of the train. An additional radar sensor was installed at George Bush to give a positive indication of a train's arrival at the intersection and as a way to "narrow" the wide angle speed measurement by linking the measured speed with a point presence. A Microwave Sensors doppler motion detector is used for this task and installed on the southwest traffic pole above the Whelen sensor.
David Rickerson enjoying a "fun day in the sun"
Both sensors were modified to enable the direction sense to be changed remotely. Since the sensor can only "look" in a single direction, the central train monitoring software must send messages to the Whelen and Microwave Sensors devices to set the appropriate direction. The sensor defaults to looking for southbound trains but switches to the correct direction upon train arrival in the corridor. This limitation will be overcome in future radar sensors scheduled for deployment.
Pole cabinet for PTZ video equipment (larger box) and small box for the rail monitoring equipment
Communications to the site is provided by a shared single mode fiber line (in cooperation with the City of College Station) and a 900 MHz data radio installed on the southwest traffic pole. The data radio operates through a repeater mounted within the corridor and enables low power communication throughout the project area. At this time the data radio handles all the rail monitoring information while the fiber handles video, camera control and the traffic signal rail preempt monitoring at George Bush, Joe Routt and West Main crossings (George Bush and the next two crossings to the north). A prototype RS485 multidrop linear communication network was tested that linked each of the traffic cabinets (George Bush, Joe Routt and West Main - a distance of approximately 3600 feet) with excellent results.
Fiber Optics
A fiber optic splice canister. Very rugged and designed for extremely harsh environments.
To enable TTI researchers to receive full motion video from the George Bush site, a connection was required into the City of College Station's new single mode fiber backbone running along Wellborn Road. TTI, with the help of City CS and TAMU Telecommunications, embarked on a project to build a comm link between the two separate systems. Since the TAMU fiber was designed to be strictly a cross campus link, there was no fiber termination box in the area. A connection point between City CS fiber and TAMU fiber was identified and the process to connect them was underway. Fiber connections in the field are formed by creating a splice (also the method for repairing damaged fiber). Fiber splices are very rugged and must withstand the elements. As you can see this one is laying in a tub. Another splice in the same box is submerged in dirty muddy water.
Constructing fiber splice
The following pictures show the process of creating a fiber splice. The first image shows the inside of a fiber splice canister. You can see two heavy fiber cables coming into the rear of the device. The cable is broken down inside the splice to reveal the human hair-sized communication fiber. There are several levels of protection for the fragile fibers. Luckily the fiber is very strong if pulled but weak if bent. The technician must take care once the actual fibers are handled to minimize the radius of any turns in the fiber. Light can escape from a fiber curving at a sharp radius.
Using the cleaver and fusion splicer to build a top quality connection
The fibers from each cable must be very accurately coupled to introduce minimal perterbation to the light wave traveling down the fiber. Any mismatches in a connection will create a reflection and a portion of the light will be sent back to the transmitter. The fiber ends are fused to create a homogenous glass path for the light. The fusion machine is complex but no too difficult to use. Before getting fused, the fiber ends get precisely cut by the cleaver to produce a clean perpendicular cut. The fibers are then introduced to the machine which grabs the fibers and holds them. The operator moves the fibers close and then the machine takes over to precisely maneuver the fiber together to just the right geometry. The two pieces of glass are then quickly fused to finish the job.
Fiber junction box in a traffic signal cabinet
With the splice complete, attention focuses on creating a "glass path" from the TTI field cabinet to the TransLink TMC Lab. The connection between the City and TTI is made in a nearby traffic signal cabinet. The City installs fiber termination boxes in each of their signal cabinets along the corridor. The fiber is "jumpered" from the incoming or "east" fiber bundle to the outgoing or "west" bundle. At this box, the TTI fiber is connected with TAMU fiber for the final run to the TransLink Lab.
Testing the fiber link with an OTDR
After the fiber splice is complete and an end-to-end run is established it is time to test the link. Optical fiber is very efficient but poorly done splices and/or connectors can degrade a system. An Optical Time Domain Reflectometer (OTDR) is used to send light down the fiber and then "listen" for reflections. The reflections are caused by any defect along the light path. Measurements are made on the amount of light that is lost during the trip from one end to the other. The measurements are used when purchasing equipment. The communication equipment will define a "loss budget" that specifies how much of the incident light can be lost in a link.
