struct TrafficLight {
  const uint8_t greenPin;
  const uint8_t yellowPin;
  const uint8_t redPin;

  void begin() {
    pinMode(greenPin,  OUTPUT);
    pinMode(yellowPin,  OUTPUT);
    pinMode(redPin,  OUTPUT);
  }

  void off() {
    digitalWrite(greenPin, LOW);
    digitalWrite(yellowPin, LOW);
    digitalWrite(redPin, LOW);
  }

  void red() {
    off();
    digitalWrite(redPin, HIGH);
  }

  void yellow() {
    off();
    digitalWrite(yellowPin, HIGH);
  }

  void green() {
    off();
    digitalWrite(greenPin, HIGH);
  }
};

TrafficLight lights[] = {
  {2, 3,  4},
  {5, 6,  7},
  {8, 9, 10}
};

void setup() {
  for (TrafficLight& aTrafficLight : lights) aTrafficLight.begin();
}

void loop() {
  for (TrafficLight& aTrafficLight : lights) aTrafficLight.red(); // all lights red
  delay(300);
  for (TrafficLight& aTrafficLight : lights) aTrafficLight.yellow(); // all lights yellow
  delay(300);
  for (TrafficLight& aTrafficLight : lights) aTrafficLight.green(); // all lights green
  delay(300);
}