When a vehicle shears a traffic light cabinet, it can rip up fiber cable all the way into the backbone, causing extensive costs and risk exposure. A breakaway cable connector can eliminate this.

[Editor's Note: This article was submitted on behalf of Optical Cable Corp.]

by Ed Sullivan

Although today’s intelligent, fiber optic-based traffic control systems have become increasingly powerful and popular, too many still have an inherent Achilles Heel — i.e. vulnerability. That is, when a vehicle accidentally runs into the traffic light control cabinet at an intersection, the situation can quickly become disastrous – and stay that way for too long.

The reason for this dilemma is all too well known: When impact shears a cabinet from its pad, it can also rip the fiber optic cable far beyond the cabinet’s branch segment all the way into the network backbone, bringing down the traffic control system, causing extensive repairs, and introducing risk to travelers and technicians. On top of costs of up to $30,000, miles of traffic flow may be knotted for days.

“It is somewhat paradoxical that one of the causes of all this pandemonium is the durability of the fiber optic cable,” explains Tom Hazelton of Roanoke, Va.-based Optical Cable Corporation (OCC).  “OCC is a manufacturer of advanced fiber optic cable with applications ranging from abusive military environments to the most sophisticated communications networks. And because these cables are built to withstand harsh conditions, they don’t break. As a result, when impact carries an enclosure away from its base, the cable will move with it . . . unless the cable connection is designed to do otherwise.”

Engineering a triggered breakaway

Designing a fiber optic cable connector rugged enough to last, yet would not wipe out network asset connections, required a bit of creative engineering that OCC undertook to fulfill the concept of one of its technology partners, TrueView Products, of Phoenix, AZ.

“As a manufacturer of fiber optic devices for the telecommunications industry we are naturally involved in ITS (intelligent transportation systems) application,” says Jeff Dominique, TrueView president. “So we got together with Tom Hazelton to discuss the need for a cable connection device that would disconnect positively upon impact, or when triggered by some mechanical force.”

Working together with OCC, TrueView engineers developed the IRIS connector, what they purport to be the first “failsafe” breakaway fiber optic cable connector developed for traffic light control cabinets and highway network nodes. In the event of a vehicular impact, the IRIS connector assembly — which is under positive spring tension — disengages automatically to protect the electronics of the cabinet as well as downstream fiber optic drop cabling and backbone cable. Using this connector, very expensive collateral damage to traffic system networks can be avoided, and traffic signal cabinets can be back up running in minutes instead if hours or days.

The surprise installation

The IRIS connector made its debut at a March 2009 Intelligent Traffic Engineers Conference, held at the Phoenix Convention Center. At the conference, officials from the city of Surprise and the surrounding Maricopa County’s Department of Transportation (MCDOT) first saw the IRIS in action.

“We recognized that it could offer valuable protection to the new intelligent traffic control system we were installing along a five-mile stretch of West Bell Road, a primary surprise access road that carries about 60,000 vehicles on a work day,” explains Israel Lopez, who was then a MCDOT manager on the project.

“This project was already specified at the time, but TrueView Products together with OCC agreed that we could have the IRIS connector on a beta test basis. So we were able to install the device in the traffic signal cabinets at 12 intersections without changing the spec,” says Lopez.

The IRIS connector looked very promising to Lopez not only because it would save extensive damage and related costs that were incurred when a vehicle clobbers one of these cabinets, but would also reduce the related hazards that occur when extensive damage is done to a traffic communications network that supports message boards, traffic sensors and TV observation cameras connected to the MCDOT traffic management system.

Dominique explains that the avoidance of  “collateral damage” to backbone cabling is the main benefit of the new breakaway connector. The fiber optic cable feeder line runs underground alongside the city streets, he says. At about 250 feet from the traffic light control cabinet at an intersection, a drop cable is connected to the backbone. Without a breakaway connector at the front end of the drop cable (in the control cabinet), a severe impact can shear the cabinet off its pad and cause collateral damage by jerking the drop cable so hard that it destroys the connection with the backbone cabling, possibly disabling some of the traffic control systems sensors, cameras and communications devices in the process.