Final answer:
Double solid yellow lines indicate that passing is not allowed in either direction on a two-way road, ensuring road safety.
Step-by-step explanation:
The type of lines that indicate passing is not allowed in either direction are double solid yellow lines. These lines are usually seen on two-way roads and are intended to signal to drivers that passing other vehicles is not safe or legal in either direction. These lines play a critical role in maintaining road safety by clearly defining the rules for overtaking other vehicles. When you see double solid yellow lines on the road, it means that both directions of traffic are prohibited from crossing these lines to pass.