void setup()
{
  for(int i=2;i<=7;i++){
    pinMode(i, OUTPUT);
  }
}
void traffic( int R1,int Y1, int G1, int R2, int Y2, int G2){
  digitalWrite(2,R1);
  digitalWrite(3,Y1);
  digitalWrite(4,G1);
  digitalWrite(5,R2);
  digitalWrite(6,Y2);
  digitalWrite(7,G2);
  
}
void loop()
{
  // Step 1
 traffic(1,0,0,0,0,1);
  delay(15000);
  // Step 2
 traffic(1,0,0,0,1,0);
  delay(5000);
 // Step 3
 traffic(0,0,1,1,0,0);
  delay(15000);
  // Step 4
  traffic(0,1,0,1,0,0);
  delay(5000);
 
}