What line type is used for stop bars?

The proper indication for stop bars at an airport is represented by a single row of red lights. These lights are used to inform pilots and ground vehicle operators that they must stop at a specific point, ensuring safety and compliance with air traffic control instructions. The red lights provide a clear and immediate visual cue, particularly important in high-traffic environments like an airport, where quick recognition of stop lines is crucial for preventing accidents.

In contrast, solid and dashed yellow lines are typically used in various roadway contexts to indicate different types of traffic flow and restrictions but do not directly apply to the operation of stop bars on an airside environment. Thus, the use of a single row of red lights is the standard for indicating stop bars, making it the correct answer in this context.