What is the primary role of clearways in relation to TODA?

The primary role of clearways in relation to Takeoff Distance Available (TODA) is indeed to provide an extension to the available takeoff distance.

Clearways are designated areas beyond the end of a runway that are free of obstacles and can be used during the takeoff phase of a flight. By allowing for a clear area where aircraft can safely accelerate and take off, clearways effectively increase the distance an aircraft can utilize for takeoff. This extension is crucial, especially in situations where an aircraft may require more distance to reach the necessary speed for liftoff, particularly with heavier loads or in adverse weather conditions.

In contrast, options like serving as a backup landing area, improving taxiing speed, or enhancing runway lighting visibility do not accurately capture the primary function of clearways. While clearways do improve safety by providing a clear area free from obstacles, their main function is directly tied to the takeoff process and helping ensure aircraft can safely achieve flight in varying circumstances.