Safe passing zones are indicated by __________.

Safe passing zones are indicated by broken or dashed yellow lines on the roadway. This type of line means that passing is allowed, as it signifies that the lane is open for drivers to overtake slower-moving vehicles. The presence of the dashed lines informs drivers that it is safe to cross into the opposite lane to pass another vehicle, provided it is clear and safe to do so.

In contrast, solid yellow lines indicate that passing is not permitted. Double yellow lines also signify that no passing is allowed, as they represent a separation of traffic traveling in opposite directions, typically in areas where visibility is limited or where road conditions make passing unsafe. Therefore, the correct answer reflects the road markings that specifically designate safe zones for passing other vehicles.