The effect of traffic management measures may be improvement of travel time reliability. Reliability may be increased by a reduction of travel time but also by a reduction of travel time variability. Travel time variability incorporates both travel time delays and uncertainty in travel time. It may be expected that objectively measured travel time variability differs from the subjective experience and expectations of this variability. Furthermore, traffic information may influence the experience of travel time variability without influencing the objective travel time variability. To arrive at a tool suited to assess changes in travel time variability on a national scale, Goudappel Coffeng carried out a study for the Dutch Ministry of Transport. In this study travel time variability is operationalised from both an objective and subjective point of view. Objectively measured variations in travel time and subjective experience and expectations of travel time variability in trips are measured. This is done for trips by cars and trucks from door-to-door. Different data collection techniques are used (a driver panel study using trip-diaries, black-box data from trucks and questionnaires).
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