The analysis of the variability of vehicle trajectories can reveal important information about how situational constraints influence drivers' behaviour (e.g., lateral position and/or speed). Variability in the lateral position using a driving simulator was examined. Forty-two participants had to drive on two road environments: a 3 km straight road with a crest vertical curve (CVC) with perceptual treatments and narrowed lane width with subsequent provision of a hard shoulder, by relocation of the road markings. The results showed that, on the one hand the lateral position variability was greater when driving on the test CVC, before meeting oncoming vehicle and on the narrowed lane width; and on the other hand it was limited according to the perceptual treatment used. The lateral position variability would be a difficulty indicator of road geometry which would inform road managers of the presence of a risk zone on their road network.