If you are travelling in the dark, use your high beams when approaching traffic is NOT within ____ feet?

Some drivers make the mistake of always using low beams. This seriously cuts down on their ability to see ahead. Use high beams when it is safe and legal to do so. Use them when you are not within 500 feet of an approaching vehicle. Also, do not let the inside of your cab get too bright. This makes it harder to see outside. [California Commercial Driver Handbook]