Ealing Friends of the Earth defend traffic forecasts
Christine Eborall dismisses claims that tram data is unreliable
Will French of Save Ealing’s Streets states: “TfL’s traffic forecasts are so unreliable that TfL will not discuss, explain or justify them. TfL has removed the forecasts from its website and they form no part of the documents currently being consulted on. No information has been provided on the assumptions that went into the forecasts but it is clear that they are based on TfL’s highly questionable theory that traffic in West London will evaporate when the tram has been built.”
This is a typical response from people a campaign which cannot refute the traffic projections, so it resorts to rubbishing them. Please can I set the record straight?
Firstly, it is simply not true that the forecasts have not been discussed, explained or justified. During the Local Consultation Groups, which were conducted between March 2003 and July 2004, and attended by representatives of Save Ealing’s Streets as well as representatives of many other community organisations, presentations by and questions to TfL’s consultants Scott Wilson provided a lot of information about the traffic projections. In addition, Scott Wilson did a 4 hour special presentation and Q&A session on traffic modelling on 5 August 2003 in the Telfer Room in Ealing Town Hall, which Save Ealing’s Streets representatives attended. There are also four Information Sheets on traffic modelling which were originally produced in 2003 for the Local Consultation Groups, and which Save Ealing’s Streets representatives have therefore had for many months, and which are now available on TfL’s website.
Secondly, on several occasions Scott Wilson consultants have explained the basis of and the assumptions that have gone into the model. The model is based on extremely detailed information about the current situation: road usage, public transport usage and population data (see TfL information sheets for more information).
The assumptions include:
And the without-tram scenario assumes among other things:
Thirdly, the traffic forecasts cannot be dismissed as ‘unreliable’. Of course, as with any forecasting technique, they can only provide estimates of future travel patterns and will always be subject to margins of error. But similar modelling predicted the reduction in traffic levels that would occur after the introduction of the congestion charge in central London (and remember how all the disbelievers fell silent once it came in? and those forecasts took a worst case view, as is usual, and consequently under-estimated the traffic-reducing effect of the charge). The Scott Wilson modelling has been thoroughly tested to ensure that it replicates at the micro level what is actually happening, and is also taking a worst case view about the extent to which people will switch to the tram.
Fourthly, traffic evaporation is not a theory – it is a proven fact. TfL’s consultants and other specialists have access to an accumulating body of data, derived from observations in many parts of the country of the effects of town centre pedestrianisation schemes, protracted road works and road capacity reductions, including the Hammersmith Bridge closure. What happens is that traffic is re-distributed over a wide area. These data have been incorporated into the Scott Wilson traffic modelling.
Still don’t believe me? Have a look at “Disappearing traffic: the story so far”, a 2001 research paper which examines the effect of roadspace reallocation in over 70 case studies in 11 countries. It’s available as a .pdf file on University College London’s Transport Studies Unit website: www.cts.ucl.ac.uk/tsu
Save Ealing’s Streets seems to be misunderstanding what the modelling is telling us. The traffic projections show that, with the tram, there will be changes to traffic behaviour over a wide area. To suggest, as Save Ealing’s Streets is doing, that there will still be 27,000 or even 25,000 vehicles a day battling to stay on or close to the Uxbridge Road is to completely misunderstand what the modelling is telling us.
In a nutshell, the modelling shows two scenarios:
1. With the tram: drivers over a wide area will know that the Uxbridge Road has less space for traffic and therefore will change their behaviour accordingly. Many will avoid the area altogether. The number of vehicles still seeking to use it will be about 19,000 a day, i.e. 8,000 or 30% less than now. Many stretches of the Uxbridge Road will be able to accommodate this. In the few places where it can’t, traffic management measures will come into effect to control access to residential roads and traffic flows on them. Where will the 8,000 go? Using the detailed traffic forecasts, we estimate that about 1,500 (conservative estimate) will switch to the tram, 3,000 will use local roads within 1 km either side of the Uxbridge Road, and 3,500 will avoid the area altogether and be dispersed across the wider West London road network.
2. Without the tram: drivers will continue to treat the Uxbridge Road as a traffic route. By 2011, over 30,000 vehicles a day will be trying to use it, i.e. 11% more than now. When they find it’s congested, drivers will seek local shortcuts and rat-runs through exactly those residential streets which Save Ealing’s Streets says it wants to save. And, apart from one-off schemes for which Ealing Council will have to bid for money in competition with all other London boroughs, there will be no traffic management measures in place to prevent this.
August 10, 2004