You may not cross a single broken white or yellow line:

1. When doing so would interfere with traffic. ✓
2. When turning left into a driveway.
3. When the car in front of you is disabled.
4. When passing to the right on a one-way street.

Answer: A. When doing so would interfere with traffic.

You may not cross a single broken white or yellow line when doing so would interfere with traffic.

Why this is the answer

The handbook treats a broken white or yellow line as permission to cross only when the move is safe. It says you may cross a broken line to pass or when the right half of the road is closed, but not if crossing is unsafe or the line is solid yellow. Another passage says broken or dashed lines let you pass or change lanes only if safe. So the limit is about safety and traffic interference, not the specific turn, disabled vehicle, or one-way passing situations listed.

Why the other answers are wrong

• B. When turning left into a driveway. — A left turn into a driveway is not listed as a reason you must stay off a broken line; the handbook's limit is whether crossing is safe.
• C. When the car in front of you is disabled. — A disabled car ahead is not named in the passages as a broken-line crossing restriction; the passages speak about passing and safety, not that situation.
• D. When passing to the right on a one-way street. — Passing to the right on a one-way street is not prohibited by these passages; one passage says with broken white lines on a one-way road you may drive in any lane.

Remember it

Think of a broken line as a maybe, not a yes: it only allows the move when traffic and safety allow it.