Why is there a DANGER:DO NOT ENTER sign posted above the tunnel at Long Beach Airport?

    If those square neon letters are lit, apply the brakes because a hazard may lurk inside: carbon monoxide, a car accident, the Cloverfield monster. Seriously, that sign is hardly ever illuminated. It was useful when the tunnel opened in 1958. Back then the air was so nasty that folks used to don gas masks. Officials were concerned that a thick haze could fill the tunnel with toxins and do in drivers. It’s a good thing that we’ve cleaned up our act since those smoggy days.
    Illustration by Zohar Lazar