int SwitchState=0;
void setup() {
  pinMode(7, INPUT); //switch
  pinMode(6, OUTPUT); //greenlight
  pinMode(5, OUTPUT); //redlight 1
  pinMode(4, OUTPUT); //redlight 2
}

void loop() {
  SwitchState = digitalRead(7);
  if (SwitchState == LOW){ //if switch is off
  digitalWrite(6, HIGH);
  digitalWrite(5, LOW);
  digitalWrite(4, LOW);
  }
  else{
  digitalWrite(6, LOW);
  digitalWrite(5, HIGH);
  digitalWrite(4, LOW);
  delay(250);
  digitalWrite(5, LOW);
  digitalWrite(4, HIGH);
  delay(250);
  }
}