Advanced Portable Emissions Monitoring System for buses

MQT on 2015-02-23
Session date: 
February 23, 2015
Question By: 
Darren Johnson
City Hall Greens
Asked Of: 
The Mayor


Last year, buses in Brighton were fitted with an advanced Portable Emissions Monitoring System (PEMS) equipment and artificially loaded with ballast representing a 70% passenger load. Multiple trips were conducted in normal traffic during business hours, stopping at regular bus stops in a similar manner to the normal passenger service. Why does Transport for London regard it as impractical to do this with a selection of older buses in London, so that we get more reliable real world data?


Answer for Advanced Portable Emissions Monitoring System for buses

Answer for Advanced Portable Emissions Monitoring System for buses

Answered By: 
The Mayor

Brighton does not have its own emissions test cycle. London does and the TfL emissions test replicates real-world driving conditions for the capital and is conducted independently at a proving ground so vehicles can be compared in an identical way. The London Buses emissions test cycle is a more accurate way to measure exhaust emissions of all types and can eliminate outside influences which might distort results.

To assure itself of the efficacy of selective catalytic reduction (SCR) equipment in actual service, TfL also fitted NOx sensors to a vehicle as a secondary check.  This less precise form of measurement of nitrogen oxides can be added to the SCR unit during the retrofit stage but TfL cannot incorporate sensors into new engine systems as these might conflict with the computer management software of manufacturers.

NOx sensors are not the same as externally-fitted portable emissions measurement systems (PEMS) which are quite bulky and protrude from the rear of the exhaust system. These tend to be used in test environments that are free from traffic. TfL regards them as unsuited to the London operating environment.