How Low-voltage Intelligent Traffic Systems Deliver Benefits in Safety, Cost and Efficiency

Significant change is coming to the intelligent traffic systems (ITS) that control intersections across North America, bringing increased efficiency and safety at lower cost to municipalities that adopt the new technology.

The change involves ITS cabinets that run on low-voltage DC power, as opposed to the traditional 120 volt cabinets that now power traffic lights.

Cabinets are being outfitted with more and more equipment as the ITS systems live up to their name by becoming increasingly intelligent. Adaptive signal controls, emergency vehicle preemption, traveler information systems and incident monitoring are all contributing to the proliferation of increasingly complex equipment in these roadside cabinets.

Up to now, it all ran on 120-volt AC power, but LED technology in the traffic lights is paving the way for new low voltage cabinets that let municipalities take advantage of the benefits of this technology shift. We’re now seeing ITS cabinets that run on low-voltage (LV) technology, specifically 48-volt DC power, which delivers some important benefits.

First is increased safety. When a 120-volt signaling light gets knocked down, whether by a vehicle collision or weather event, you’ve got the potential for a live, 120-volt line to cause real damage. If it falls on a car, it could energize the occupants. It’s also a hazard to emergency responders and any pedestrians in the area.

A 48-volt line, by comparison, is below the 50-volt cutoff to be considered “touch safe.” In simple terms, that means it won’t kill you to touch it. LV technology delivers safety benefits even in normal operation, such as if the door of an ITS cabinet is open while a technician is working on it – there’s no risk of shock or worse.

LV cabinets also deliver cost savings in a number of ways. Because they are below the touch safe threshold, there’s no requirement for a licensed electrician to install or service the cabinets. Also, OSHA typically requires technicians wear personal protective equipment (PPE) when working on high-voltage cabinets. Such equipment tends to be bulky and difficult to maneuver in, which slows workers down. There’s no requirement for such protection gear with LV cabinets, making installation and maintenance quicker and easier.

Use of highly efficient LED lights delivers additional cost savings. The 120-volt cabinets cannot take advantage of the latest efficiency gains in LED technology. The newest LED lamps draw as little as 3 watts, but the 120V cabinets do not work properly with LEDs that draw less than 12 watts. Why? Because the sensors in the cabinet can’t detect such low wattages; they’ll think the light has burned out and will place the intersection in flash mode, with blinking yellows and reds. With LV cabinets, municipalities get the full cost benefit of the latest LED technology.

Additional cost savings come from the uninterruptible power supply (UPS) technology used in the cabinets. In a traditional cabinet, AC power feeds the cabinet where an online UPS converts the voltage from AC to DC, and then back again to AC, which is output to the load. If the signal uses LED bulbs, there’s another conversion in the LED power supply from AC to DC. In each conversion there’s a small tax to be paid in terms of power loss.

LV cabinets, on the other hand, receive AC power from the utility, convert it to DC and output the DC power directly to the load. Savings from eliminating conversions will vary depending on the exact equipment involved, but it’s estimated to be about 5% to 10%. Multiplied over dozens or hundreds of traffic lights, that’s a significant savings.

APC by Schneider Electric is contributing to the new LV architecture by supplying the power management unit (PMU) that delivers the proper voltages to the equipment in the cabinet and provides battery backup, to ensure intersections don’t go dark during a power outage, accident or other event.

It’s early in the game yet for LV ITS cabinets but the technology makes so much sense that we’re confident it’s the wave of the future. To learn more, click here.