int red = 10;
int yellow = 9;
int green = 8;

void setup(){
pinMode(red, OUTPUT);
pinMode(yellow, OUTPUT);
pinMode(green, OUTPUT);
}

void loop() {
  changeLights();
  delay(15000);

}

void changeLights(){
// green off, yellow on for 3 seconds
digitalWrite(green, LOW);
digitalWrite(yellow, HIGH);
delay(3000);

// turn off yellow, then turn red on for 5 seconds
digitalWrite(yellow, LOW);
digitalWrite(red, HIGH);
delay(5000);

// red and yellow on for 2 seconds (red is already on though)
digitalWrite(yellow, HIGH);
delay(2000);

// turn off red and yellow, then turn on green
digitalWrite(yellow, LOW);
digitalWrite(red, LOW);
digitalWrite(green, HIGH);
delay(3000);
}