2-wire versus 3-wire APS: What’s the difference and which do I need?

Polara offers two versions of APS, each with unique installations and benefits. Here, we explain some of the key differences to help you select the one that’s right for your intersection.


There’s no such thing as “one size fits all” when it comes to accessible pedestrian signals (APS). Installations, be they retrofits or new construction, require careful consideration of a multitude of factors, from where to locate the pole to how to wire the system. 


While many Accessible Pedestrian Signals on the market require additional wires between the pedestrian signal head (commonly referred to as “the ped head”), push button station (PBS), and control unit, Polara’s systems are designed to work with existing wiring–or to operate as a stand-alone system if wiring isn’t already in place. 


In this article, we’ll cover some of the key differences between the two versions of our industry-leading iDS/iNS APS with a view toward helping you select the one that’s right for your intersection.


Two-wire system


A two-wire system is designed for intersections where pedestrian signals and call buttons are already present. Conductor wires from the previously installed conventional push buttons are used to connect the new PBS to an “intelligent central control unit” (iCCU) in the traffic cabinet. Up to 16 PBS and 8 signal phases can be operated from a single iCCU.


By utilizing existing button wires and adding just one box to the cabinet, Polara’s patented two-wire system allows cities to upgrade to APS simply, cost-effectively, and without the issues that come part and parcel with other systems. (Many devices and features require additional wires, which can be difficult, and sometimes impossible, to lay if the original conduits aren’t big enough, or are too old/damaged to feed new wires through.) 


Besides a simpler and faster installation, Polara’s two-wire system provides the maximum features and performance possible, including automatic sound synchronization, preemption for emergency vehicles and trains, remote monitoring and system alerts, and improved transient protection. More about these features can be found on our product page and documentation.

Both our iDS2 and iNS2 models can operate as two-wire systems.


Three-wire system


A three-wire system is designed for intersections without push buttons and button wires. These are generally either pre-timed crossings (i.e. where signals are automated rather than being activated by a pedestrian) or are new crossings without any existing infrastructure. (A three-wire system can also be used at intersections with button wires for call activation.)


Rather than connect to an iCCU in the traffic cabinet, the three-wire system uses an “intelligent ped head control unit” (iPHCU) that installs in the ped head via three wires: power, ground, and data. Each PBS connects to its own iPHCU, meaning it responds only to the messaging provided by the ped head it’s connected to and operates independently of any others that may be installed at the intersection.


While there are advantages to a stand-alone system, it’s important to note that not all the features of a two-wire system (like preemption and remote communication) are available on a three-wire system. A wireless sync feature can be used to synchronize sounds between PBS on the same phase, so that a button press on one unit enables the same Walk and Clearance sounds on a linked unit. A remote ped call option can also be enabled so systems can communicate with our PedApp Pedestrian Mobility App.

Our iDS2 and iNS2 models can operate as three-wire systems; our iDS3 and iNS3 models can only operate as three-wire systems.



This article focuses on the differences between Polara’s two- and three-wire systems, but they share much in common, including rugged, quality components, secure wireless programming, and compatibility with both our Field Service App and PedApp. Both models offer cities a durable, reliable, and feature-rich solution for enhancing the accessibility of their signalized crossings and pedestrian networks.


Still have questions about two- and three-wire systems?


>>Visit our iDS/iNS product page

>>Get in touch with us