The misselling of congestion charging/traffic filters

The introduction by Oxfordshire County Council of traffic filters/congestion charging in Oxford has been marked by repeated and serious failures of integrity, including suppression of important information and the appearance of public consultation when in fact decisions had already been taken.1
Here, I expose how technical data has been used in a way which is misleading and sometimes just plain false.

I'm not one of those who think that any restriction on the use of private cars is outrageous. I lived for many years in London entirely happy with congestion charging. It may be right for Oxford. But I'm not arguing the case either way here: rather, I'm concerned with the honesty with which technical data is being used. Professionally, I had considerable experience of the misuse or misinterpretation of data for political or ideological ends, and it's something I've always felt strongly about.

I'm going to look at three areas: road accident casualties; air pollution; and traffic volumes. In each case, comparing what the council's consultative document says or implies, with what the data actually says.

Road accident casualties

What the council say: traffic casualties in Oxford are ‘unacceptable’, with over 1700 accidents reported in Oxford 2015-2019 resulting in over 2000 casualties. This is due to ‘high levels of traffic’. ‘Most road casualties are concentrated in the city centre and on the main roads leading there’. ‘Road safety is a major barrier to people walking and cycling’. ‘In...the Oxfordshire Cycle Surveying 2019, over 60% of people said that traffic levels and road safety were their main concerns’. It would be reasonable to infer from all this that casualty rates are rising, or at least, are stubbornly high.

What the data says: in reality, there's been a steady reduction in casualty rates over many years - over 50% since 2000. See Graph 1, from OCCs Road Casualty Statistics 2019. It is not possible to say exactly what caused this decrease. It mirrors national trends and most of it occurred before the Liberal Democrats took over the county council, so it's not something that  the Council can take credit for. There was a small uptick in 2024, but casualties are still below the level they were pre-Covid.

The council aggregate data for four years, 2015-19: no reason is given for doing this and it appears it is done just create a bigger figure. This is misleading - particularly since in each of those years, the number of casualties was falling.

The data does not show any correlation between traffic volumes and casualty rates. See Graph 2. Thus, the council's assertion that casualties are caused by high traffic volumes appears untrue.

In the latest casualty report there is a map showing where accidents have occurred. Although it's difficult to read in detail, it's clear that none of the 20 fatal casualties occurred in Oxford and of the serious casualties. It looks like more occurred on the ring roads than city itself. If that interpretation of the map is correct, then the councils statement that most casualties occurred in the city centre and roads leading to it is incorrect.

The published report on the Oxfordshire Cycle Survey 2019 does not contain any data bearing out the council's assertion that over 60% of respondents said traffic levels and road safety were their main concerns. The only relevant data, figure 10 of that report, is where respondents cited problems on their particular route (note: just ‘problems’, not ‘main problems’). There, 26% raise issues of ‘traffic safety’. None of the categories relate to ‘traffic levels’. You could only reach 60% by adding in categories such as ‘ junction safety’ and ‘no cycle lane’: but these as likely to be the consequences of poor road design of high traffic volumes. Or they may simply reflect the fact that, for example, turning right on any road against the traffic is an inherently risky maneuver for a cyclist.

Conclusion: the consultative document is misleading in failing to recognize that casualty rates have been falling over several decades. The aggregation of four years data has no justification. The statements that over 60% of respondents in the cycle survey said that traffic levels and road safety were their main concerns, and that poor safety is the result of high traffic levels, do not seem to be true, according to the published information. The statement that most casualties or concentrated in the city centre and the main roads leading there is unclear, and it is not clear that the data supports this statement.

Air pollution

What the council says: ‘air pollution is a major public health risk’. ‘In Oxford 40% of nitrogen dioxide comes from transport .’ ‘There is no ‘safe’ level of air pollution: the World Health Organisation is clear that even low levels can be harmful to human health over the long term’. ‘One of the fastest ways to improve air qualities is by reducing the use of private cars.’ Again, it is a reasonable inference from the document that air pollution levels are getting higher, or at least are stubbornly high.

The data: the reality is that - as with traffic casualty rates - there's been an extraordinary reduction in air pollution in Oxford over many years. Again, most of this improvement predates the existing administration, and mirrors national change and the improvement is due to many factors which includes improvement in car engine design and fuels.

The City Council publishes annual air quality reports which are densely technical, and virtually invisible to the general public. Taking each of the main pollutants in turn.
Nitrous oxide: levels have fallen by 2/3rds since 2004 and are now below the city council's own targets and at current rates would appear likely to fall below the WHO recommended level within a year or two and indeed are already below the WHO level for the High Street and St Ebbes.
Pm 10 levels have been falling since monitoring began in 2011 and are now already below the WHO recommended level at High Street and St Ebbes.
Pm 2.5: rates have fallen significantly since 2011 are now below the WHO recommended level in St Ebbes though not in the High Street.

Thus in reality air pollution levels in central Oxford are enormously better than they were and are now below or very near the WHO recommended levels. This must be why the document suggests the WHO don't believe that any level of pollution is safe . But that is not what the WHO guidelines in fact say. They say: ‘available evidence cannot clearly identify levels of exposure that are risk-free’. This is in a section of the WHO guidelines which discusses how far evidence is sufficient to support recommended levels. They are saying that the evidence is lacking to set a recommended level that is known to be without harm. That is of course not at all the same thing as saying ‘there is no safe level of air pollution.’

But that is not all. The council pay no attention to an important piece of research, the Oxford Source Apportionment Study, which looked at exactly what is causing different kinds of air pollution. It turns out that in central Oxford, which is the area in which congestion charging seeks to reduce car traffic, road transport is not the dominant pollution. For nitrous oxide, the dominant pollution is domestic combustion, with cars contributing a mere 5%. For PM10, the dominant pollutant is production processes, with cars again only contributing 5%. For PM2.5 , there are many sources of pollution including military aircraft and boats, with cars only contributing 6.5%. Thus, the councils statement that in Oxford, 40% of nitrogen dioxide comes from transport, does not appear to be true.

The council also perversely ignores the impact of electric cars. The proportion of new cars sold that are electric rose by 20 percent last year. Manufacturers are under an obligation to meet stretching targets for increasing the proportion of cars sold that are electric, reaching 100% in 2035. Thus, air pollution from cars will rapidly reduce without any intervention by the council.

Conclusion: the council have suppressed the truth that air pollution levels of have fallen dramatically over several decades and in many cases are aleady within WHO recommended levels. The council appear to have rephrased the statement in the WHO guidelines, in a way which significantly shifts the meaning. The statement that 40% of nitrous dioxide in Oxford comes from transports appears untrue. Ignoring the impact of increased sales of electric cars on air pollution is perverse. The statement that the fastest way to improve air quality is by reducing use of private cars is doubly wrong, first because there were many years when traffic volumes have been increasing but pollution was decreasing, and secondly because in reality the contribution private cars make to air pollution on Central Oxford is marginal.

Traffic volumes

What the council says: as the economy and population continues to grow so does traffic on our roads. In 2019 the total vehicle miles driven in Oxfordshire passed 4 billion for the first time.The inference is that road traffic volumes in Oxfordshire have been growing continuously for some time.

What the data says: Department of Transport figures give a different picture. (Note that the county council's figures do not match the departments figures.) See graph 3.
 
The Department of Transport data for traffic miles traveled on the county’s roads show that for the first 14 years of this century, traffic volumes did not rise at all, there was then a rise until 2019 when there was a very sharp fall due to covid. Although last year's figures are up, they are still below the pre-covid peak.

Overall conclusion
In its statements about road traffic casualties, air pollution and traffic volumes, the county council shows a pattern of misrepresentation and of false statements which is unacceptable and concerning. Together with other lapses of integrity in process, it appears the council has deliberately misled the public. The Liberal Democrats a heavy responsibility for having engendered the bitter division within our community on this issue, and for having contributed to the collapse of faith in democratic government which is such a worrying feature of our times.


Note

1. See for example:  Oxford Traffic filters: Major details hidden from public | Oxford Mail https://share.google/JzZgf6LHo2QAmazB5

Congestion charge decided ‘behind closed doors’ – BBC News https://share.google/MhBsSUnM4YZnLppwH

Oxford traffic filters: pressure mounting on council | Oxford Mail https://share.google/6yWKlRtjeL1jQJvYs