Which of the following is true regarding Iowa’s traffic lane markings?

In Iowa, double solid lines serve a specific purpose concerning lane discipline and traffic flow. These markings indicate that lanes of traffic are separated and that crossing these lines is prohibited. This is particularly common on roads where safety concerns exist, such as near curves, intersections, or in areas where changing lanes could create dangerous conditions. The presence of double solid lines ensures that drivers remain in their designated lanes, thereby reducing the risk of collisions between vehicles traveling in opposite directions or for drivers attempting to pass when it is unsafe.

The other choices provide incorrect interpretations of traffic markings. For example, single solid lines do not permit passing; indeed, they suggest caution. Dashed lines indicate areas where lane changes are permitted, not restrictions on stopping. Traffic flow being required within marked lines is a basic principle of driving, but it does not encompass the specific regulatory context provided by the other markings indicated in the question.