Multi-Aspect Signal Mast Controller

// Three-aspect signal controller
const int RED = 9;
const int YELLOW = 10;
const int GREEN = 11;

enum Aspect { STOP, APPROACH, CLEAR };
Aspect currentAspect = STOP;

void setup() {
  pinMode(RED, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(GREEN, OUTPUT);
}

void setAspect(Aspect aspect) {
  // Fade out current, fade in new
  analogWrite(RED, aspect == STOP ? 255 : 0);
  analogWrite(YELLOW, aspect == APPROACH ? 255 : 0);
  analogWrite(GREEN, aspect == CLEAR ? 255 : 0);
}

void loop() {
  setAspect(currentAspect);
  delay(100);
}