from machine import Pin
from time import sleep

l1 = Pin(18, Pin.OUT)
l2 = Pin(17, Pin.OUT)
l3 = Pin(16, Pin.OUT)

while True:

    l1.on()
    l2.off()
    l3.off()
    #red / stop

    sleep(6.0)

    l1.off()
    l2.off()
    l3.on()
    #green / go

    sleep(6.0)

    l1.off()
    l2.on()
    l3.off()
    #yellow / caution

    sleep(1.0)

    #l1.on()
    #l2.on()
    #l3.off()
    #yellow and red 

    #sleep(0.25)