This study proposes a Lane Change Assistance (LCA) system that provides haptic guidance during lane changes. This system is fully integrated with Lane Keeping Assistance (LKA) functionality to provide continuous lateral support during highway driving. Two different system configurations of this LCA are investigated. One is a generalized LCA and the other is an adaptive LCA that provides personalized lane change reference trajectories through trial-by-trial adaptation to lane change duration of previous lane changes. The effects of these systems with respect to mental workload, lateral control performance and user acceptance are investigated. This is done during an experiment with three different driving sessions, consisting of a manual session and two sessions in which either the generalized or adaptive LCA is active. The experiments are conducted on a 6 DoF motion-based simulator with 34 participants, driving in a simulated three-lane highway environment with a scripted traffic scenario. To measure mental workload, an auditory cognitive secondary N-back task is introduced. The results show that the introduction of a generalized or adaptive LCA does not significantly influence the measured mental workload. When the adaptive LCA is introduced, lateral control performance and subjective usefulness is enhanced compared to the generalized LCA and manual driving.