#define RED 2
#define YELLOW 3
#define GREEN 4
#define EMERGENCY_BIN 7
enum TrafficState{
  NORMAL_TRAFFIC, EMERGENCY_OVERRIDE
  };
  TrafficState currentState = NORMAL_TRAFFIC;
  void setup() {
    pinMode(RED,OUTPUT);
    pinMode(YELLOW,OUTPUT);
    pinMode(GREEN,OUTPUT);
    pinMode(EMERGENCY_BIN,INPUT_PULLUP);
  }
void normalTraffic(){
  digitalWrite(GREEN,HIGH);
  delay(4000);
  digitalWrite(GREEN,LOW);

  digitalWrite(YELLOW,HIGH);
  delay(2000);
  digitalWrite(YELLOW,LOW);

  digitalWrite(RED,HIGH);
  delay(4000);
  digitalWrite(RED,LOW);
}
void emergencyMode(){
  digitalWrite(GREEN,HIGH);
  digitalWrite(YELLOW,LOW);
  digitalWrite(RED,LOW);
}

void loop() {
  if(digitalRead(EMERGENCY_BIN)==LOW){
    currentState=EMERGENCY_OVERRIDE;
  }
  switch (currentState){
    case NORMAL_TRAFFIC:
    normalTraffic();
    break;

    case EMERGENCY_OVERRIDE:
    emergencyMode();
    break;
  }
}