When must you stop before crossing a drawbridge?

When approaching a drawbridge, the necessity to stop is primarily guided by the presence or absence of signals indicating its status. Stopping is required when there is no signal light or traffic control attendant to direct traffic. This ensures safety, as drawbridges can raise to allow vessels to pass through, and without proper signals, drivers cannot ascertain whether it is safe to cross.

In situations where signals are not functioning or an attendant is absent, stopping provides critical time to assess the bridge's condition and any potential hazards that may not be immediately visible. It's important for drivers to be vigilant, as a lack of clear signals does not always mean it is safe to proceed.

The other options suggest scenarios that may not require a stop, but they do not account for the essential condition of signal absence which necessitates a cautious approach to ensure safety on the road.