int red = 4;
int green =  2;
int yellow = 3;
void setup()


{
    pinMode(4, OUTPUT);
    pinMode(3, OUTPUT);
    pinMode(2, OUTPUT);
}
void loop(){
    changeLights();
    delay(5000);
}

void changeLights()

{
    // green off, yellow on
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
    delay(3000);


    // turn off yellow, then turn red on
    digitalWrite(3, LOW);
    digitalWrite(4, HIGH);
    delay(3000);

    // red and yellow on for 2 seconds / red is already on
    digitalWrite(3, HIGH);
    delay(3000);

    // turn off red and yellow, then turn on green
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    digitalWrite(2, HIGH);
    delay(3000);
}