int redLEDPin = 11;
int greenLEDPin = 10;
int yellowLEDPin = 9;

int timerRed = 2000;
int timerGreen = 2500;
int timerYellow = 1500;

void setup() {
  // put your setup code here, to run once:
  pinMode(redLEDPin, OUTPUT);
  pinMode(greenLEDPin, OUTPUT);
  pinMode(yellowLEDPin, OUTPUT);

  // initialize as 0
  digitalWrite(redLEDPin, LOW);
  digitalWrite(greenLEDPin, LOW);
  digitalWrite(yellowLEDPin, LOW);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(redLEDPin, HIGH);
  digitalWrite(greenLEDPin, LOW);
  digitalWrite(yellowLEDPin, LOW);
  delay(timerRed);
  digitalWrite(redLEDPin, LOW);
  digitalWrite(greenLEDPin, HIGH);
  digitalWrite(yellowLEDPin, LOW);
  delay(timerGreen);
  digitalWrite(redLEDPin, LOW);
  digitalWrite(greenLEDPin, LOW);
  digitalWrite(yellowLEDPin, HIGH);
  delay(timerGreen);
}