Various policy measures are available to help control traffic congestion and pollution problems. Typically, local planners wish to model their effects before implementation. Many computer models exist, but it is not yet clear which sort of model is the most suitable for assessing each type of measure or package of measures.
AIUTO aimed to develop a framework of models and methods for the simulation and evaluation of Transport Demand Management (TDM) measures. TDM policies include:
- pricing measures, e.g. road pricing, parking charges, public transport fares and cordon charges;
- regulatory measures, e.g. zone access control, parking restrictions, traffic calming and priority for public transport measures;
- supply systems, e.g. park & ride and dial-a-ride.
The project defined a set of key indicators as the minimum comparison level for sites across Europe, and a common framework of recommended modelling methods.
Alternative approaches to modelling of local transport demand were shown to give results that were not significantly different. However, in the case of modelling traffic flows on the road network, models with greater disaggregation were found essential for:
- assessing the effects of traffic-responsive control signals;
- accurately estimating air pollution and safety indicators.
Hypothetical packages of TDM measures were evaluated for six test sites across Europe. The findings are site-specific, but give some indications of lessons for other cities. For example:
- Incentive (‘pull’) measures such as an increased public transport service, if applied alone, were found rather ineffective in stimulating a switch from private cars. By comparison, ‘push’ measures such as parking and cordon charges altered the modal split significantly.
- Combinations of pull and push measures (e.g. park & ride facilities, parking charges plus restricted access zones) yielded the greatest reductions in car trips - more than 21% in Salerno. Restricted access alone also had a substantial effect.
- Staggered working times across companies and flexibility of working hours within companies was found to decrease vehicle-kilometres and especially the levels of exhaust pollution.
Although AIUTO has demonstrated that adequate modelling capabilities to analyse TDM measures are generally available, some test site results have shown significant discrepancies in the modelling predictions (e.g. for air pollution). This suggests that validation tests would be useful for a better assessment of the accuracy of such models.
Existing software tools typically are heavily data intensive and require substantial investment in user training. AIUTO has recommended the development of a set of common user-friendly tools that would permit quicker and easier analysis of TDM measures in any European city.
The test site results point to the importance of applying packages of TDM policies, rather than individual measures. Packages increase the modal switching benefits (e.g. through synergistic effects), and are perceived to increase the social acceptability of car trip reduction.