Many European policymakers consider road-pricing as a credible instrument to tackle urban congestion.

New research shows that in Paris, lower income motorists would benefit from schemes that include rebates for 'greener' vehicles or seek to combine greater reductions in vehicle numbers with faster journey times on public transport.

Congestion charging schemes need to consider the level of traffic reduction sought alongside the perceived fairness for different income groups of the scheme. New research compared the direct effects - i.e. the monetary cost and the changes in travel time - of nine possible road-pricing scenarios for commuters in Paris.

These were:

* a toll on traffic travelling in or through Paris, at different price levels from 0.70 Euros to 4.25 Euros per trip, geared at reducing traffic by 10, 20, 30 or 50 per cent

* charging only traffic entering Paris from the suburbs * charging in the central zone but providing a 90 per cent reduction in the charge for residents

* charging in the central zone but reducing by 50 per cent the toll for 'greener' vehicles (less than 180g CO2 per km)

* using the proceeds of a charge to reduce the cost of public transport

* distributing the proceeds of a charge evenly among all commuters in the form of lump-sum payments

The researchers investigated which groups of commuters - motorists or public transport users - were winners or losers in terms of toll cost and reduction in journey time under these scenarios. Variables included the cost of cars versus public transport, the value placed by different income groups on reduced travel times, availability of free parking, household income, number of children and number of cars per household.

There is a strong correlation between income levels and the value placed on journey time. Comparing different schemes shows how scheme design and the degree to which journey times are improved affects the pattern of take-up among commuters. On the whole, motorists tend to lose financially by the introduction of tolls. However, higher-income motorists do lose less than lower-income motorists, among those who continue to use their car following the introduction of a toll.

Lower-income motorists would increasingly switch to public transport if toll income is used to subsidise public transport. Lower-income motorists would be hardest hit by the scenario that charged motorists entering a zone from outside, as they tend to live in the suburbs. Political acceptability of the scheme would be improved if city centre residents were partially exempted. Lower income motorists could benefit from a rebate for greener vehicles. In relative terms, tolls are always more detrimental to lower-income groups as a percentage of income. But in absolute terms, the results depend crucially on how much the traffic is reduced by. If higher tolls lead to greater traffic reduction, and motorists who switch to public transport lose less in terms of time and money, more stringent tolls can in fact favour lower-income individuals.

Source: Bureau, B. and Glachant, M. (2008). Distributional effects of road pricing: Assessment of nine scenarios for Paris. Transportation Research Part A: Policy and Practice. 42 (7):994-1007. Contact: Theme(s): Sustainable mobility, Urban environments