The report now shows that the Mayor's Taxi Age Limit is improper and as far as exhaust emissions are concerned, older taxis are no worse than the new taxis. In fact the new TX4 taxis are shown to create more NO2.
The report from Defra also shows that ALL emission strategies in London have so far failed.
Below is an except from the report which deals specifically with Taxis:
4.3 London taxis
The locations of the central London survey sites at Aldersgate Street and Queen Victoria Street resulted in a large number of taxis (black cabs) being surveyed. Over 15,000 observations of taxis were made, the majority being LTI TX1, TXII, and TX4 models. As a result of the relatively large sample size, the emissions from taxis can be disaggregated in more detail than most other vehicle types.
Current TfL regulations stipulate that annual licences are only issued to taxis that are under 15 years old and meet Euro 3 emissions standards. This is achieved either by (a) operating a vehicle originally manufactured to Euro 3 standards (or later); (b) retro-fitting approved emissions reduction equipment; or (c) using an LPG conversion. The Mayor has also set out proposals to have a taxi capable of zero emission operation in regular use by 2020. Such a taxi would effectively address all taxi-related local emissions. LTI TX1 models (Nissan engines) were originally manufactured to Euro 2 emissions standards, whereas later LTI TXII models with Ford engines (introduced around 2002) were manufactured to Euro 3 emissions standards. LTI TX4 models with VM Motori engines (introduced around 2006) were originally built to Euro 4 standards, with a Euro 5 compliant version introduced in 2012. Other observed taxi types with much smaller sample sizes include the LTI FX, the Carbodies Metrocab, the Mercedes Vito 111 (Euro 4), and the Mercedes Vito 113 (Euro 5).
Figure 25 NOx/CO2 emissions from London taxis by year. (2008)
Previous research based on remote sensing surveys implemented in London in 2008 (Rhys-Tyler et al., 2011) had identified statistically significant changes in both nitric oxide emissions and smoke emissions with the introduction of the LTI TXII and LTI TX4 taxi models. In the transition from the LTI TX1 model to the LTI TXII, it was observed that nitric oxide emissions reduced by more than half; however, at the same time, smoke (particle) emissions (as measured using ultraviolet opacity techniques) were observed to increase around threefold. With the introduction of the LTI TX4 model around 2006, smoke (particle) emissions reduced below the levels of the earlier TX1 model, whilst nitric oxide emissions remained at statistically similar rates to the TXII model.
Figure 26 NO2/CO2 emissions from London taxis by year. (2012)
The patterns observed in the earlier research based on 2008 data are replicated in the 2012 data set, although we now have the advantage of both NO and NO2 measurements, and a much larger sample size. The plots of NOx vs. year of manufacture shows clear groupings of vehicles, which broadly split into two categories of higher and lower emissions of NOx. In terms of significant numbers of taxis, the largest reduction in total NOx occurred with the transition from the LTI TX1 model (4132 observations), to the LTI TXII model (4050 observations). However, the infrared opacity measurements confirm that smoke (particle) emissions from the LTI TXII model continue to be much higher than from other taxi types, both newer and older.
Figure 27 NO2/NOx emissions from London taxis by year.
There is a clear indication that absolute levels of NO2 emissions from taxis manufactured since around 2008 have been increasing. This is true for the LTI TX4, and the Mercedes Vito models. The newest versions of the Mercedes Vito taxis (manufactured in 2011 and 2012) are observed to have the highest absolute emissions of primary NO2. The fraction of primary NO2 in total NOx (f- NO2) from the taxi fleet is observed to increase significantly for taxis manufactured since around 2009, with substantial variation between manufacturers. Whilst f-NO2 was typically below 10-12% prior to 2005, LTI TX4 models manufactured in 2011 and 2012 have f-NO2 values of around 27%, whilst the Mercedes Vito models manufactured in 2011 and 2012 have f-NO2 values of around 35-40%.
Given the intensity of taxi operations in the centre of London, the increase in levels of NO2 emissions from the newer taxi fleet is a matter of concern for local air quality management in general, and NO2 limit values in particular. The high levels of smoke (particle) emissions from LTI TXII taxis also warrants further investigation. Both of these issues should be taken into consideration when developing future policy for taxi emissions. The technologies adopted by manufacturers require further investigation to gain a full understanding of the generation processes for total NOx, f-NO2, and particulate matter, with a view to minimising the pollutants of concern in future vehicles.
The whole report can be downloaded here
Goto/ 1. REMOTE SENSING OF NO2 EXHAUST EMISSIONS FROM ROAD VEHICLES (PDF 2.31 MB)
: 13/05/2013 (Uploaded: 20/05/2013)
See page 45 4.3 taxis and page 47 chart 27 showing that the newer taxis cause MORE NO2 than the older cabs.
This report shows that TX2 taxis are causing more pollution overall than any others; therefore an age limit is not proper. Overall it shows that most technologies for reduction of diesel pollution in an urban environment do not work.
With many thanks to research carried out by Dave Davies.