Policy: Ancillary Impacts

Evidence drawn from London indicates that: 1) Congestion has fallen within the charging zone since the introduction of the scheme; 2) predicted increases in congestion in the area surrounding the charging zone has not materialised; 3) bus and average car speeds inside the central charge zone have increased from 10.9 to 11.6 km/h and 14.3 to 16.7 km/h respectively (TfL, 2003; TfL, 2003a; 2004; TfL, 2004a; Santos and Bhakar, 2005). Although the increase in vehicle speeds within the charging zone is marginal, there are important links between vehicle speed and emissions (Kakkad and Rossiter, 2007).

Congestion charging also has important implications for air quality. Between 2002 – 2003, estimates for London indicate that when market advances are made in vehicle technology and non-exhaust emissions (i.e. particulate emissions from tyre and brake wear) are taken into account, reductions were realized in NOX emissions by 8% and PM10 by 6% within the charging zone (TfL, 2007). However, on the Inner Ring Road, emissions of NOX were unchanged, and there was a 3% increase in PM10. However, it is difficult to measure the precise impact of emission reductions on measured concentrations of pollutants since air quality strongly reflects weather patterns and background pollution (TfL, 2006).

Modelling data varies over the theoretical benefits of congestion charging. For example, Daniel and Bekka (2000) predicted that vehicle emissions (NOX, CO and HC) could be reduced by up to 30% in the most congested areas (Beevers and Carslaw, 2005). However, recent life-cycle analysis (LCA) of the potential environmental impacts of an emissions related congestion scheme in London reveal negligible impacts on emissions of PM10 and NOX in 2009 from cars within the charging zone. Moreover, should there be an increase in the overall numbers of cars driving in the charging zone over the longer-term, there is likely to be a corresponding increase in air pollutant emissions (AEA, 2007).

One of the central impacts of congestion charging is time savings gained by motorists. Variation in the level of congestion equates to a change in the specific nature of car travel, especially when considering individual drivers. How individual value time under pre-charging conditions is an important determinant of the impact of a charging scheme upon him/her. In the presence of congestion, time value has been estimated to increase up to 40% (MVA et al., 1987 in Santos and Bhakar, 2005). Wardman (2001), using meta-analysis also indicates that time spent in congested traffic is valued 50% higher (Santos and Bhakar, 2005). Additionally, stated preference techniques indicate that in very heavily congested conditions motorists place nearly twice as much weight on their time compared to free-flow conditions (Steer Davies Gleave, 2004 in Santos and Bhakar, 2005).

Congestion charging can have unintended impacts upon road safety both positive and negative. Less vehicle travel within a charging zone may result in fewer traffic collisions, while causing more casualties among pedestrians, cyclists, and motorcyclists due to a shift in transport mode and behaviour. Moreover, due to the potential for increased vehicle velocity within a charging zone there may be changes in the severity of accidents that do occur. Case evidence can be drawn from the London Congestion zone where TfL (2006) estimates an overall reduction of casualty accidents during the charging hours within the charging zone (including the Inner Ring Road). Accidents reduced by 4% outside the charging hours compared to 7% for the rest of London. As a result, TfL suggests there has been a 2–5% reduction in casualties attributable to the congestion charging scheme (TfL, 2006). Noland et al. (2008) indicate no statistically significant effect for total casualties in London, but within the charging zone a statistically significant drop in car occupant casualties, and possibly an increase in cyclist casualties.

Increased road safety can be translated into cost savings. Transport for London estimates that the scheme is responsible for between 40 - 70 additional accidents saved per year translating into benefits between £5 - 10 million per year (TfL, 2005d in Santos and Fraser, 2007). However, Santos and Fraser (2007) indicate that the savings are more likely between £2.1 - 3.7 millionper year and suggest that there was a long-term downward trend in both the number of accidents and casualties in London that is unrelated to the congestion charge but rather to accident reduction measures.