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How it worksEl Paso's system of 104 signs and eight closed-circuit televition (CCTV) video cameras piggy-backs on a fiber-optic sonet ring installed along the freeway. The $3.8 million project was developed and installed with a Federal Highway Administration Congestion Mitigation Air Quality (CMAQ) grant that required a 20% state match. Source: Walter P. Moore

In 2003, a Texas state senator was stuck in traffic for hours when a truck overturned on a section of road near El Paso — the state's fifth-largest city — without service roads or obvious alternative routes. His subsequent request for a way to alert drivers on such roads to their nearest alternative route led the Texas DOT (TxDOT) to develop a product that's being introduced at this month's Intelligent Transportation Society of America's 20th Annual Meeting & Exposition.

Combining existing sign design, construction, and communications interfaces into a unique system, the nation's only “automated diversion device” is also a logical outgrowth of El Paso's federally required incident management plan.

TxDOT began working with other agencies to define diversion routes and standard operating guidelines based on incident severity and location. A GIS comprised of interactive, retrievable maps graphically defines routes, as well as agency roles, responsibilities, and first-responder contact information, so the agency's El Paso District office can direct traffic through the area during emergencies.

Then the agency began looking for a way to automate guidance along detour routes. The system had to:

  • Have a low per-unit cost, because more than 100 signs were needed
  • Be solar-powered, because neither AC nor DC power is available on some routes
  • Comply with American Association of State Highway and Transportation Officials and Texas Manual on Uniform Traffic Control Devices standards
  • Have a high-intensity reflective coating because of the unavailability of direct lighting on alternative routes
  • Deliver two to three very specific messages, not full dynamic messaging
  • Communicate via wireless Ethernet technology.
  • No off-the-shelf sign met all the criteria, so a completely new device was developed: an automated guidance system/rotary drum sign.

    Made of high-grade aluminum, the lightweight 5x3-foot signs are easily mounted on standard pedestrian poles. Each sign is comprised of four rotating drums with three sides per drum, allowing for three messages per sign. Each message, and the entire sign face, is covered in 3M high-intensity reflective sheeting (Series 2800/6800) to reflect ambient light from headlights and streetlights, eliminating the need for external lighting.

    The wireless, solar-powered signs require no fiber-optic cable or hard-wire communications interconnect. Instead, sign and camera information is transmitted to fiber-optic sonet (synchronous optical network) nodes installed along the freeway, which send the information to the traffic operations center. There, data is translated into a format that allows it to interact with the center's dynamic message sign (DMS) control software. When operators activate the signs, the command is carried back through the sonet network, then to the wireless network, and finally to the signs.

    Most of the time, the signs display standard information. But when activated, the drums rotate to provide detour information. At transmission speeds of up to 100 megabytes/second, communication between the traffic operations center and the signs is virtually instantaneous. The signs change in less than a second, alerting drivers on an entire stretch of roadway simultaneously.

    — Mark Conway (mconway@walterpmoore.com), PE, is Director of Intelligent Transportation Systems for Walter P Moore.