A well-known phenomenon in traffic management is that after an improvementt in the traffic conditions, the traffic volumes increase and as a consequence the traffic conditions deteriorate again to a level close to the situation before the improvement. The reasons for the increase in flows are a combination of the following: 1. Rerouting: traffic is rerouted from longer parallel routes to the shorter and now also faster route. 2. Change of departure time: people choose again for travelling in the peak hours. 3. Trip length modifications: travellers choose destinations on a longer distance because the shorter travel times allow longer distances. 4. Suppressed travel demand: people make trips that they wanted already to make but that were not feasible within the time budget they originally had. 5. Induced travel demand: people change their travel behaviour and make more trips because the conditions have improved (e.g. people take a job because travelling to the job has become feasible or teleworkers decide to work at their office again). Another effect is that people choose other places to live, in a more attractive place further away. 6. Modal shift: the car becomes more attractive than public transport, walking, cycling and the need for car-pooling is reduced. 7. The growth of population or economic situation. The first 6 reasons have a direct relation with the improvement of the traffic conditions. The relation with the 7th reason is only indirect. The growth of the traffic volume due to improvements in capacity or better utilization of existing capacity make the investments in most conditions still worthwhile, even if the net reductions of travel times are small or zero. In some conditions there is no net profit, however. Apart from the impact of improved travel conditions on travel behaviour of persons, similar effects can be observed for freight transport. For the covering abstract see ITRD E124693.
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