Smart Intersection — Adaptive Traffic Signals over LoRa

What it does

Smart Intersection is an adaptive signal control system that sets traffic light timings according to the traffic actually arriving at the junction, rather than a fixed schedule. Sensors on each approach measure vehicle count, average speed and queue build-up; the data travels over a LoRa radio link to a central unit, which redistributes green time so that busier directions get a larger share.

The system looks beyond simple counts. Because it also knows vehicle speed, slow or stopped traffic can be given higher priority than heavy but free-flowing traffic. Waiting pedestrians are treated as demand too, and a minimum crossing time is always preserved.

Emergency vehicles such as ambulances and fire engines receive full priority, while public transport receives conditional priority. As an emergency vehicle approaches, its direction is brought to green without skipping any safety intervals; for buses, the green phase is extended or brought forward. After the priority event, the approaches that were held back are rebalanced with compensating green time.

How it works

The system has three layers:

• Sensor nodes: Radar-equipped units mounted on poles along each approach measure incoming flow and queues before vehicles reach the stop line, and report them to the central unit in short data packets.
• Central unit: Runs the decision algorithm. It condenses the demand from each approach into a single score and calculates the cycle length and the split of green time.
• Signal controller: Drives the lamps. Plans from the central unit can only change timing parameters; they can never alter the phase sequence or the safety rules.

The control loop works on a scale of seconds: instead of reacting to every single vehicle, the system optimises phase durations over short windows. Instant safety functions, including amber time, all-red clearance and interlocking of conflicting greens, always remain in the signal controller's own firmware. A new plan takes effect at the end of a cycle, never mid-phase, and any plan that fails validation is rejected while the current one continues.

If the radio link drops, the junction keeps running. The signal controller falls back to the last valid plan stored in memory, or to a fixed-time backup plan. Radio is the optimisation layer of the system, not its safety layer.

Operating scenarios such as morning peak, night mode or event days are defined in a web panel and distributed to the devices with a version number. Even if the internet connection is lost, the junction continues with the last scenario it received.

Technology

• Hardware: Nodes use an ESP32 processor with a Semtech SX1276 LoRa radio. Vehicles are detected with 24 GHz Doppler radar sensors.
• Communication: Sensor data and phase commands are carried over LoRa. A single junction uses raw point-to-point LoRa; scaling to multiple junctions is planned on a ChirpStack-based LoRaWAN architecture. The payload format and decision algorithm are identical on both, so moving between them only changes the transport layer.
• Frequency band: The EU868 band is used within the limits of the Turkish short-range device (KET) regulation issued by BTK.
• Security: Packets are encrypted and signed with a message integrity code (MIC); sequence numbers ensure that replayed or forged packets are discarded. Priority requests rely on a whitelist and a separate key per vehicle, and every priority passage is logged.
• Algorithm: Cycle length and green split are calculated using the Webster method, widely used in traffic engineering, within fixed lower and upper safety limits.

Where it is used

The system is designed for adaptive signal management at single junctions, along arterial corridors and at multi-leg intersections. A four-way junction, a corridor of several junctions and a multi-leg intersection with a diagonal road were all modelled in simulation, including pedestrian phases and priority vehicle passage, and their behaviour was verified. Prototype hardware has since been built and tested; no field pilot has been carried out yet.

Installation on a real road requires compliance with traffic signal standards and approval from the relevant authorities. For that reason, work on a scale-model junction is planned before moving to the field, with sensor and traffic parameters to be calibrated during a future pilot installation.