The present disclosure relates to a method performed by a road segment determining system for identifying beforehand a situation with a potentially in-alert driver of a vehicle. The road segment determining system determines a position of the vehicle, and further determines pre-stored road characteristics of a road segment assumed or known to be ahead of the vehicle. Moreover, the road segment determining system determines the road segment to be monotonous based on comparing at least a first road parameter of the pre-stored road characteristics with predetermined monotonous road criteria. The disclosure also relates to a road segment determining system in accordance with the foregoing, a vehicle comprising at least a portion of the road segment determining system, and a user device comprising at least a portion of the road segment determining system.