enum TrafficState {
 STATE_RED,
 STATE_YELLOW,
 STATE_GREEN
};

TrafficState currentState = STATE_RED;
// 2 ->  Red
// 4 -> Green 
// 5 -> Blue , Will be used for simplicity instead of Yellow
void showState(TrafficState s) {
 digitalWrite(2, s == STATE_RED ? HIGH : LOW);
 digitalWrite(4, s == STATE_GREEN ? HIGH : LOW);
 digitalWrite(5, s == STATE_YELLOW ? HIGH : LOW);
}

void setup() {
 pinMode(2, OUTPUT);
 pinMode(4, OUTPUT);
 pinMode(5, OUTPUT);
}

void loop() {
 showState(currentState);
 delay(1000);

 if (currentState == STATE_RED) {
   currentState = STATE_GREEN;
 } else if (currentState == STATE_GREEN) {
   currentState = STATE_YELLOW;
 } else {
   currentState = STATE_RED;
 }
}