City of Dallas Flooded Roadway Warning System: Migrating 42 Sites from Proprietary SCADA to ALERT2

The challenge: a proprietary SCADA system at end-of-life

For more than a decade, the City of Dallas relied on a Flooded Roadway Warning System to keep drivers off low-water crossings during flash flood events. The system uses 42 master sites distributed across the city, each connected to two or more slave sites — the roadside “HIGH WATER WHEN FLASHING” signs that motorists actually see. When the water-level float switch at a master rises above its trigger level, the master tells its slave signs to start flashing. When the water recedes, an operator presses the Reset button and the lights go out.

The system worked. The problem was the equipment behind it. The original SCADA manufacturer had stopped supporting its proprietary communications protocol, and replacement parts and firmware updates were no longer available. The City was facing a stark choice: replace the entire field infrastructure with another vendor's proprietary system — and risk being in the same position again in ten years — or migrate to a non-proprietary, standards-based protocol that the City would never be locked into.

The City chose the open-standard path and looked for a vendor that built equipment around ALERT2, the National Hydrologic Warning Council's open telemetry protocol for flood warning networks. HydroLynx Systems had recently completed the conversion of its own flood warning equipment from ALERT1 to ALERT2, so the City asked HydroLynx to design a prototype that would fit inside the existing field cabinets without requiring civil work or replacement of solar power and battery infrastructure.

The constraints that shaped the design

The City's specifications added real engineering constraints beyond simply “make it work with ALERT2”:

• Drop into existing cabinets. The new electronics had to physically fit inside the City's installed enclosures so field crews could swap boards without replacing poles, solar panels, batteries, or signs.
• Reduce power draw. A typical FRWS site runs on solar and battery — every milliamp matters during long, cloudy storm seasons when the flashing lights are most likely to be active.
• Keep the operator interface familiar. Field technicians already knew how to interpret the original control box LEDs (Active / Lights Out / Reset) and which button to press to clear an event. The new system needed to preserve that same human-interface model.
• Support remote control from the city office. Dallas operations staff needed to monitor every site and override states (force lights on, force lights off, disable float-switch control) from a centralized desk over a secure connection.

The HydroLynx telemetry architecture

HydroLynx designed a three-radio architecture that uses each band for what it's best at: licensed VHF for long-haul reporting to the central base station, unlicensed 900 MHz spread spectrum for short-range master-to-slave coordination, and cellular for management and reprogramming.

Control logic and operator interface

The flashing-light control logic preserves the operational model field crews and city staff are already trained on:

• Water rises above trigger level. The master sends a 900 MHz remote-control-on command to all its slave sign sites. Each slave closes the relay that powers its flashing LEDs. The Active LED on every control box (master and slaves) turns on; Lights Out and Reset LEDs turn off.
• Water recedes below trigger level. The master transmits the new float-switch state to slaves over 900 MHz. The Active LED turns off and the Lights Out LED turns on — but the flashing lights stay on. Roadway warning systems intentionally require human acknowledgment before lights go dark, to prevent premature reset while standing water remains on the roadway.
• Operator presses Reset. When an operator presses Reset on either the master control box or any slave control box (a slave press is relayed to the master over 900 MHz), the master broadcasts a remote-control-off command. Slaves open the relay and the flashing lights go out. The Lights Out LED turns off and the Reset LED turns on, indicating the site is back to standby.

The same seven remote-control commands are also available from the base station: turn lights on regardless of float-switch state, turn lights off regardless of state, enable or disable float-switch control entirely, force an immediate data transmission, reset the master, or reset all slaves connected to a master. Commands can be issued through the ALERT2 VHF receiver/decoder or through the cellular gateway, giving operators two independent paths during severe weather.

What each site monitors

Beyond the binary float-switch state, the redesign instruments each site with diagnostic data that allows the operations team to spot a failing battery, a damaged LED string, or a tampered cabinet before a flood event exposes the problem:

Master station data

• Water level float switch state (digital, sampled every second)
• Water level in feet from an analog pressure transducer (sampled every minute)
• Battery voltage
• GPS time-sync status
• Control-box button states (Reset, Lights Out)
• Control-box LED states (Active, Lights Out, Reset)
• Cabinet door-open status

Slave (sign) station data

• Flashing-light relay status and output state
• Flashing-light relay voltage and LED currents
• Control-box button and LED states
• Battery voltage
• Cabinet door-open status
• Reset count since last firmware reset

Once a day, between midnight and 1:00 AM at a randomized offset (to avoid base-station collisions across all 42 masters), each master also transmits metadata: total reset count, transmit packet count for the day, TDMA frame length, TDMA slot length, TDMA slot offset, and internal clock state. This nightly heartbeat gives the operations team a continuous health record for every site without consuming daytime radio bandwidth.

Sign and hardware redesign

The migration was also an opportunity to simplify the field hardware:

• Changeable signs replaced with fixed signs. The original system used motorized changeable signs that could display different text. The redesign uses a single fixed “HIGH WATER WHEN FLASHING” sign, eliminating a moving mechanical part and the “Lights Out” button used to control it. The button remains on the control box for backward compatibility but is no longer wired to anything.
• New low-current LEDs. The replacement flashing-light LEDs draw roughly half the current of the originals. Across a 12-hour active event this materially extends battery runtime — important for sites that stay active through multi-day rain bands.
• DIN-rail relays instead of panel-mount. The previous flashing-sign panels used a single panel-mounted relay, but Dallas slave sites needed four. Panel-mount relays were too big to fit four into the slave box. The redesign uses DIN-rail relays that stack closely together, fitting all four within the existing cabinet footprint.

Equipment used in this deployment

The redesign team

Underlying flooded-roadway warning sign technology licensed by Blue Water Design.

Why this matters beyond Dallas

Many municipalities operating flooded-roadway warning systems, low-water crossing notifications, or stream-gauge networks are facing the same end-of-life decision the City of Dallas faced. A proprietary SCADA vendor stops supporting older firmware. Replacement boards become impossible to source. The agency is told the only path forward is a forklift upgrade to that vendor's next-generation proprietary platform — at which point the cycle restarts on a new ten-year clock.

The Dallas FRWS upgrade is a working example of an alternative: keep the field cabinets, masts, solar panels, and signs you already own; replace only the internal electronics with ALERT2-compliant equipment; and gain a non-proprietary protocol that any compliant vendor can support going forward. The ALERT2 standard is maintained by the National Hydrologic Warning Council and published openly, so no single manufacturer can again hold an agency's network hostage.

If you operate a flooded-roadway warning system, a flash-flood notification network, or any SCADA-based hydrological telemetry approaching end-of-life, the City of Dallas pattern is directly applicable.

Case study based on a presentation by David C. Leader, Contractor System Engineer at HydroLynx Systems, Inc. For technical questions on this project, contact dleader@hydrolynx.com.