ESTABLEZCAMOS ALGUNOS HECHOS Y VALORACIONES

This section reviews the key outcomes from TfL’s investigations of the possible causative factors underlying the observed trends in congestion inside the western extension zone.

TfL’s general approach to further understanding this issue is described and previous conclusions are briefly reviewed. Recent congestion trends for the western extension zone are then considered in the light of a range of possible causative factors that are known to have applied during 2007 and into 2008.

TfL’s previous assessment

In the context of the original central London congestion charging zone, the analysis presented in TfL’s Fifth Annual Impacts Monitoring Report identified a wide range of factors that might be making a contribution to reducing the effective capacity of the road network.

Some of these were relatively obvious and corresponded to widely-acknowledged general trends affecting the central London road network. Increased road and street works was a primary example. Others were potentially more subtle, for example, changes to the mix of different vehicles within stable overall traffic volumes. It was recognised that some of these factors, which numbered in excess of 20 in total, were probably more significant than others in affecting congestion levels, and that the impact of different interventions was likely to be compounding, rather than simply additive. It was also felt that all of the identified factors were operative to some degree and that several had intensified significantly over the period since 2005. Furthermore, there were few examples of factors or inventions that had an effect of increasing the effective capacity of the road network. On the contrary, major

permanent schemes such as the remodelling of Trafalgar Square and the accelerated replacement of infrastructure by the utility companies implied significant long-term reductions to the effective capacity of the road network. The main thrust of TfL’s traffic signal management effort was therefore orientated towards mitigating, as far as was possible, the acknowledged negative affects of these various interventions on day-to-day network operation.

In recognition of the need to better understand these effects, TfL specified a long- term research project which would ultimately allow it to understand the relative impact of specific interventions, and hence facilitate better network management and planning on a London-wide basis. This project is making good progress with initial outputs expected in autumn 2008.

In relation to the loss of congestion benefits initially achieved with congestion charging in the original central London zone during 2005 and 2006, TfL presented an analysis in the Fifth Annual Impacts Monitoring Report that argued that:

• Increasing congestion and static or declining traffic flows were a long term feature of the road network in London, although the trends appeared to have accelerated since the year 2000.

• In view of changed priorities for the use of the road network in central London, reflecting various mayoral and borough initiatives, continued comparison of post charging conditions against a static baseline reflecting conditions in 2002, before the introduction of the original scheme, was increasingly inappropriate.

• A more appropriate comparison was therefore against conditions that would have prevailed in the notional absence of congestion charging – given similar competing demands on road network capacity as were seen in 2005 and 2006.

• Viewed in these terms, road users in the original central London congestion charging zone were therefore experiencing congestion reductions that could be considered broadly equivalent to the 30 percent reduction achieved in the first year or so of operation.

• A substantial increase in road and street works, reflecting the sub-surface

infrastructure replacement programme, had been an important factor contributing to the deterioration of conditions in the original central London zone in 2005 and 2006. The urgency of the infrastructure replacement programme was not

disputed; and a degree of disruption was an inevitable consequence.

In addition, these competing uses of the road network had delivered substantial benefits in respect of other Mayoral transport priorities. Among the most visible and valuable were the reductions that have been achieved in reported road traffic collision casualties, both in central London and more widely; and the adjustments to road layouts, signal timings and other elements of the streetscape that have made conditions easier for pedestrians and cyclists. These interventions broadly reflected both TfL and borough policies, of which congestion reduction was only one element, albeit an important one.

Assessment of recent congestion data

Bearing in mind TfL’s previous conclusions, the new insights from the more recent data for 2006 and 2007, as described earlier in this section, are as follows:

• Conditions in the original central zone remain comparable to those of the previous year, with a sustained general loss of congestion benefits and a highly variable network performance.

• After an initial period when congestion in the western extension reduced in line with TfL’s expectations for the scheme and commensurately with the observed reduction in traffic flows, conditions from autumn 2007 rapidly deteriorated.

• From autumn 2007 to spring 2008 travel rates for traffic within the western extension zone have displayed similar characteristics to that of the original central zone. Despite the persistence of the reduced traffic flows achieved with the introduction of the scheme, congestion has deteriorated. Again this suggests that the effective capacity of the road network in the western extension has been reduced by other interventions.

• Also comparable with the original charging zone has been the general stability of conditions on the boundary route of the western extension; suggesting that these other interventions have been less intense or have been otherwise mitigated

• The rapidity of the deterioration in conditions inside the western extension is striking, suggesting that large-scale individual interventions are likely to be a significant factor.

• New data on night-time speeds are significant in that they appear to indicate a substantial loss of basic network capacity over an extended period. This could also be a significant factor in understanding daytime congestion trends. However, the statistical robustness of these new night-time data is less than the equivalent daytime data - and further survey and analysis work is necessary before these apparent trends can be confirmed and fully quantified.