uint32_t a = 0, b = 0;

void setup() {
  // put your setup code here, to run once:
  pinMode(2, OUTPUT); //Red
  pinMode(3, OUTPUT); //Yellow
  pinMode(4, OUTPUT); //Green
}

void loop() {

  if (millis() - a == 2000){
    digitalWrite(2, HIGH);//R on
  }
  if (millis() - a == 4500){
    digitalWrite(3, HIGH); //Y on
  }
  if (millis() - a == 7000){
    digitalWrite(3, LOW);//Y off
    digitalWrite(2, LOW);//R off
    digitalWrite(4, HIGH);//G on
  }
  if (millis() - a == 7500){
    digitalWrite(4, LOW);//G off
  }
  if (millis() - a == 8000){
    digitalWrite(4, HIGH);//G on
  }
  if (millis() - a == 8500){
    digitalWrite(4, LOW);//G off
  }
  if (millis() - a == 9000){
    digitalWrite(4, HIGH);//G on
  }
  if (millis() - a == 9500){
    digitalWrite(4, LOW);//G off
  }
  if (millis() - a == 11500){
    a = millis();
    digitalWrite(4, LOW);//G off
    digitalWrite(3, HIGH);//Y on
  }
}