Zero Emission Ancillaries – Developing the Evidence Base – Phase 2

Background and Challenge

This project focuses on ancillary engines used for purposes other than vehicle propulsion, which includes auxiliary transport refrigeration units (auxTRUs). AuxTRUs are climate-controlled units powered by their own auxiliary engine, independent of the vehicle's propulsion engine. Subsequently, these engines are classified as Non-Road Mobile Machinery (NRMM).  

AuxTRUs are commonly attached to heavy goods vehicle (HGVs) across cold chain logistics (temperature controlled supply chains as seen in the food and pharmaceutical markets), thus contribute to the on-road air quality mix, despite falling under the NRMM regulations. The emission contributions auxTRUs make to the transport sector remain largely unknown.  

This major work programme, funded by the Department for Transport (DfT), seeks to plug some of the data gaps on the type, quantity, emission and use profiles of auxiliary loads on HGVs and beyond. It builds on Zemo Partnership’s previous work with Transport Scotland on transport refrigeration units (Phase 1)


  • To conduct further emission testing from auxiliary transport refrigeration units (TRUs), plus other identified road-going ancillary engines (e.g. road sweepers). 

  • To conduct an industry-wide market survey of equipment numbers, types & usage patterns.  

  • To combine emission results with usage data to quantify the overall contribution of auxiliary TRUs, plus other ancillary power units to total air quality emissions.  

  • To measure the energy and emissions performance of a range of alternative technologies. 

  • To provide reports and briefings to the Department for Transport. 

Additional objectives include: 

  • Widening the scope of the project to include refrigerated vans. 

Actions and Outputs


This second phase of the project is due to run between Winter 2022 – Winter 2024 

  • Testing of HGV auxTRUs – Summer 2023 

  • AuxTRU market survey – Summer 2023 

  • Publication of the HGV Auxiliary Engines: Baseline auxTRU testing and modelling of UK impacts report – February 2024 

  • Testing van refrigeration technologies – Winter/Spring 2024 

  • Van testing report – Spring 2024 

  • Second HGV report – Autumn 2024 

  • Ongoing stakeholder engagement throughout 2023/24 

Emily Stevens

Zemo Partnership Support:
Emily Stevens

Project Officer

Brian Robinson

Brian Robinson

Commercial Vehicle Emissions Consultant

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