Sounds like you're writing for a technical manual, which you probably are. I had to read Wikipedia's entry "Automotive lighting" -- http://en.wikipedia.org/wiki/Automotive_lighting#Dipped_beam_.28low_beam.2C_passing_beam.2C_meeting_beam.29 -- to understand what you meant by passing beam (low beam headlights) and driving beam (high beam headlights). "Headlamps can emit either a passing beam or a driving beam." (But not both at the same time, right?)

If the headlights are on "high beam" this is used when there are no cars directly in front of you, and this helps you see farther down the road. You can "flash your headlights high and low quickly, to let someone know you are going to pass him. You should not use your high beams if there is on-coming traffic because it can almost be "blinding" to other drivers. When there is other traffic coming and going, you drive with the low beams at night. I have never heard of an asymmetrical headlight beam. To me that sounds like the lamps need to be adjusted. I have been to truck-driving school and have a commercial driver's license, and I can say that if there are no other drivers, you can drive with high beams. You might use the "fog lights" when there is fog, otherwise, I haven't heard of driving beams or passing beams per se.