Brakeman

The brakeman would sit in this seat to operate the brake lever

A brakeman is an amusement park employee who rides with the roller coaster to slow it down at certain points throughout the ride, particularly bends; as the train is not mechanically held on to the track. The brakeman is also responsible for stopping the train in the station at the end of the ride.

Brakemen were common on wooden side friction roller coasters but have since been made redundant by up-stop wheels. Now only a handful of roller coasters that use a brakeman still exist.