Final answer:
A solid yellow line usually marks the left edge of the roadway for traffic moving in opposite directions and indicates that passing is not allowed.
Step-by-step explanation:
A solid yellow line on roads often marks the left edge of the roadway for traffic moving in opposite directions. This is to signify that passing or overtaking other vehicles is not allowed in that lane. On two-way roads, a single solid yellow line means that traffic on the other side cannot cross over into oncoming lanes to pass; if it's a double solid yellow line, then both sides are prohibited from crossing the lines to pass. Traffic signs and road markings are designed for the orderly and safe flow of traffic, which is essential for all drivers to understand and obey.