(Bradford Council 24/12/98)
In October 1997 the Environmental Protection Department of Bradford Council carried out an assessment of the impact of the proposed relief road on air quality on Bingley Main Street. The assessment was based on the predicted traffic flows on Main Street (between Millgate and Park Road) in 1997 and 2000 and on the relief road in the year 2000. Air pollution levels were estimated 5m from the kerb using the "Design Manual for Roads and Bridges".
KDIS has attempted to extend the scope of the assessment to include 5 locations lying along a straight line perpendicular to the proposed relief road and up to 135m from Main Street. The assessment used the same model and traffic data used in our earlier assessment.
The Specialist Pollution Team did not consider levels further afield than the kerbside for two reasons:-
Pollution levels further away from Bingley Main Street will be affected by other local sources of pollution including traffic, industry and residential. To calculate accurately pollution levels further away would require information on these sources and a computer based modelling package to do the calculations, none of which were available.
Main Street is where the pollution levels are currently at there highest and the potential for human exposure is at its greatest.
The following comments can be made regarding the specific conclusions made in KDIS's report.
KDIS - " Current concentrations of Nitrogen Dioxide vary from a peak at 88 ppb (kerbside, Main Street) to 31 ppb (Bingley C of E First School) with an average value of about 60 ppb.
The assessment is seriously flawed because it does not take in to account the effect of other sources, other than traffic on Bingley Main Street, which may affect the overall ambient pollution levels (in particular traffic on Park Road which is much closer to the school than the proposed relief road).
Although the predictions for Bingley Main Street (Site C) agree with our calculations and the results of environmental monitoring, his predictions at other sites appear to either overpredict or underpredict by a large margin levels monitored using diffusion tubes. At site E for example the model predicts a level of 31 ppb (98 th %ile) in 1997 due to emissions from traffic on Bingley Main Street, however the measured annual average in 1993 at the school gives a 98 th percentile of 40 ppb. As levels are likely to have increased between 1993 and 1997 this indicates that other sources of pollution are significant. At site C, 40m from Bingley Main Street the model predicted a level of 60 ppb (98 th%ile) compared to a level of 38 ppb based on actual diffusion tube measurements made at Myrtle Court a similar distance from Main Street.
The model predictions away from the kerb do not therefore agree with the available monitoring data and must therefore be treated with caution. The model assumes dispersion in a flat open terrain with a low wind speed and takes no account of the prevailing wind direction so it is not surprising to find these discrepancies. it is particularly worth noting that the manual warns the user that the model is likely to overpredict concentrations because it assumes a low wind speed.
The concentration at site C is wrongly assumed to be the average for Bingley Town Centre. Site C is simply the mid point between Main Street and the relief road. Rather than being an average site it appears to be more representative of the margins of the town centre. In addition as the falloff in pollutant concentrations with distance from the road is not linear but exponential, one would predict that the average level occurs closer to Main Street that site C.
KDIS - (No relief road - year 2000) " Nitrogen Dioxide concentrations fall at all points: by 14% kerbside, Main Street, 26% Bingley C of E school,. 16% fall on average to 50 ppb"
The predicted reduction in levels at Bingley Main Street is in agreement with our findings. The assessment at location E, 135m from Main Street is unreliable because it fails to take in to account traffic flows on other roads such as Park Road. Monitoring suggests other local sources are significant and should therefore be included in any assessment of ambient air quality.
KDIS - (With Relief Road - year 2000) "At Main Street NO2 Levels lower than without Relief Road by 17 %"
We can agree with this conclusion
"NO2 levels 92% higher at Canal Towpath beside Relief Road"
This is not unexpected since the site is 5m from the new road where currently there is no road traffic and pollution levels are low. It is worth pointing out however that the predicted levels are lower than the kerbside levels on Bingley Main Street without the relief road. Under this scenario the peak concentrations are now at the tow path away from the town centre areas frequented by large numbers of people.
"NO2 levels 100% higher at Bingley C of E First School playground, at 46ppb approaching National Air Quality Standard background limit (set at 52 ppb). "
Much was made of the higher levels at the school if the relief road goes ahead. As already explained the assessment is flawed because it does not take in to account the effect of traffic on Park Road and other local sources. Without considering these sources no credence should be given to the predictions.
It is also important to realise that the level is below the National Air Quality Standard and if we believe the commentary in the manual to the model the actual level is likely to be a lot lower than predicted due to the conservative assumptions inherent in the model. The predicted increase is therefore not of public health concern.
"NO2 levels on average 9 % higher across Bingley Town Centre at 54 ppb (exceeding National Air Quality standard background limit)"
As already iterated, site C does not represent the average case for the town centre. If a similar location the other side of Main Street was chosen the assessment would have found levels are reduced by between 12 and 17 %. In addition the background air quality limit only applies to areas where there is housing or schools. It is my understanding that site C would not meet this criteria.
"Other toxins (particulates, carbon monoxide, benzene) show similar pattern of distribution across Bingley"
Levels of carbon monoxide and benzene will show similar distribution however the validity of this assumption in the case of particulates is not known.
Andrew Walmsley, Pollution Control Officer, Specialist Pollution Team, Bradford Council
Mr. Walmsley is right to point out that most of the findings are under-predictions of the actual pollution levels, as we ignored other traffic sources, such as Park Road. This was simply to accord with the Councils own study. The KDIS study considered only the impact of traffic on Main Street and the Relief Road. Had we included, for instance, the contribution from Park Road, then it is clear that NO2 levels at Bingley C of E school, for example, would probably exceed the National Air Quality Background Standard - which would mean that serious consideration would have to be given to closing the school. Very young children are particularly vulnerable.
Similarly, we are aware that the "assumptions" used by the Council are questionable, particularly the assumed speed of traffic on the Relief Road. The council assume 80 Km per hour, given nearly "optimum" emission levels. BETA claim this speed is more likely o be 110 Km per hour, raising emission levels by about 15%.
The use of point C as an "average" in these circumstances, whilst rough and ready, is justified as it is the midpoint between the only 2 roads under consideration. We double checked the results of this average by considering the areas under the graphs produced - these match well and so the "average" results stand up.
We also modelled predictions for Particulates (although we didn't include these in the report). They do indeed show a very similar pattern of distribution.