int TL_GREEN_LED = 2;
int TL_YELLOW_LED = 3;
int TL_RED_LED = 4;

int TrafficLightState = 0;
int TrafficLightStateNext = 10;

void setup() {
  // put your setup code here, to run once:
  pinMode(TL_GREEN_LED, OUTPUT);
  pinMode(TL_YELLOW_LED, OUTPUT);
  pinMode(TL_RED_LED, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:

if (TrafficLightState != TrafficLightStateNext){
  TrafficLightState = TrafficLightStateNext;
}

switch (TrafficLightState){

  case 10:
    digitalWrite(TL_RED_LED, HIGH);
    digitalWrite(TL_YELLOW_LED, LOW);
    digitalWrite(TL_GREEN_LED, LOW);
    delay(1000);
    TrafficLightStateNext = 20;

  case 20:
    digitalWrite(TL_RED_LED, HIGH);
    digitalWrite(TL_YELLOW_LED, HIGH);
    digitalWrite(TL_GREEN_LED, LOW);
    delay(1000);
    TrafficLightStateNext = 30;

  case 30:
    digitalWrite(TL_RED_LED, LOW);
    digitalWrite(TL_YELLOW_LED, LOW);
    digitalWrite(TL_GREEN_LED, HIGH);
    delay(1000);
    TrafficLightStateNext = 40;

  case 40:
    digitalWrite(TL_RED_LED, LOW);
    digitalWrite(TL_YELLOW_LED, HIGH);
    digitalWrite(TL_GREEN_LED, LOW);
    delay(1000);
    TrafficLightStateNext = 10;

  }


}