TfL release NOx emissions comparison in Diesel, Electric Hybrid, and LPG black cab taxis

Transport for London (TfL) recently released data comparing the nitrogen oxide (NOx) emissions of diesel, electric hybrid, and LPG black cabs, shedding light on the environmental impact of these vehicles in the city.

According to the responses obtained through a Freedom of Information (FOI) request, any new diesel TX4 taxi produced since 2016 has been built to conform to the Euro 6 emissions standard. However, such vehicles can no longer be newly licensed in London due to concerns about their environmental impact.

TfL emphasises that there can be a considerable difference between laboratory type approval tests and the emissions generated during real-world vehicle operations. To account for this, TfL refers to the COPERT emissions factors, which estimate emissions from different types of road vehicles based on their performance across various speeds and road conditions.

Using the COPERT methodology, a Euro 6 diesel TX4 taxi is estimated to emit 1.1g/km of NOx emissions in urban driving, while a Euro 5 diesel TX4 emits 1.36g/km. It is worth noting that with the installation of standard diesel particulate filters, both Euro 5 and Euro 6 diesel TX4 taxis can achieve Euro 6 standards for particulate matter emissions.

In comparison, a LEVC ZEC taxi, which is a petrol plug-in hybrid, is estimated to emit only 0.03g/km of NOx under the same driving conditions. Conversely, a TX4 taxi converted to run on LPG typically emits 0.36g/km of NOx. This means that an LPG converted TX4 taxi emits ten times more NOx than the LEVC ZEC vehicle, although it emits two-thirds less NOx than a Euro 6 diesel TX4. It is important to note that specific conditions apply for the eligibility of LPG conversion in a London licensed taxi.

Unlike NOx emissions, which are primarily influenced by engine type, CO2 emissions directly correlate with the fuel consumption of the vehicle. Based on COPERT emissions factors, the Euro 6 diesel TX4 taxi is estimated to emit 220 g/km of CO2 in urban driving conditions. In comparison, the LPG converted TX4 emits approximately 240 g/km, while the plug-in hybrid LEVC ZEC taxi emits around 55 g/km when its battery is adequately charged.

These findings highlight the substantial differences in emissions between diesel, electric hybrid, and LPG black cabs. As London continues to prioritise reducing air pollution and promoting sustainable transport, these figures provide valuable insights for policymakers and taxi operators alike.