Final answer:
A double solid yellow line on a road means that passing is illegal for vehicles in both directions.
Step-by-step explanation:
The road marking that indicates it is illegal to pass in either direction is a solid double yellow line. These lines are typically found on two-way roads where visibility is restricted or where it's unsafe to pass, such as on hills or curves. Double solid yellow lines are used to separate opposing lanes of traffic and indicate that passing is not allowed in either direction. It is important to follow these markings to ensure the safety of yourself and other drivers on the road.
When these markings are present, it means that vehicles are not allowed to cross the lines to pass another vehicle in either direction.