Scoping report: using behavioural insights to improve air quality in Merton

Project rescoping by the Behavioural Insights Team, August 2021.


The Behavioural Insights Team was commissioned by the London Borough of Merton (Merton) as part of the Local Government Association (LGA) Behavioural Insights Programme to implement and evaluate an intervention to reduce the number of cars idling outside primary schools during pick-up and drop-off times in Merton. This, and other anti-idling measures, aim to improve air quality.

We progressed this project to the design stage, however, due to COVID-19 restrictions, the project has been on hold for the past year. Infection control measures meant school drop off and pick up times changed: for example, the school where we were going to run our trial redesigned pick up and drop off to accommodate staggered start times as part of infection control measures for COVID-19. This contributed to idling outside of the school becoming less of an issue, as parents were encouraged to park and drop off in a neighbouring church parking lot. 

In consultation with Merton and the LGA, we decided to rescope the project to focus on reducing idling at level crossings. In particular, Merton is installing air quality monitors at the West Barnes level crossing in August.[1] This level crossing is located in one of Merton's Air Quality Management Areas, meaning the area where the level crossing is situated has been identified as requiring dedicated focus to achieve national air quality objectives.[2]  As part of the rescoped project, we will design and test anti-idling signage at the level crossing, and evaluate the impact of this signage using air quality monitoring data. This document sets out the rescoped project plan and activities.

Activities and timeline

We propose revisiting the evidence review that we conducted as part of our initial scoping, with a focus on idling at level crossings as opposed to outside schools. We will use the findings from this evidence review to design a message (or messages) to test on a sign at the selected level crossing. We will then write a trial protocol outlining how we will test the impact of the sign on air quality.

An updated timeline with activities for the rescoped project is listed below as well as illustrated in Figure 1.


Evidence review of idling at level crossing: September 2021

Develop messages and design intervention September-October 2021

Write trial protocol: October-November 2021

Prepare for trial launch: November 2021-January 2022 (Merton requires a 6-10 week lead time to produce the sign)

Trial period: January-February 2022 (The trial period length will depend on our outcome measure and baseline. We have used the trial period of a similar trial in Canterbury (5 weeks) as an estimate here)


Data collection and cleaning: February-March 2022

Analysis of results: March-April 2022

Write final report: March-April 2022

Incorporate comments on final report (x1): May 2022

Project management

Project management September 2021-May 2022

QA: October 2021 and April 2022.

Figure 1: a Gantt chart of updated timeline and activities

Figure 1: updated timeline and activities

Aspects to be confirmed

Prior to designing the intervention there are several aspects of the intervention and trial design that need to be confirmed:

  • Sign dimensions and positioning: We will need to confirm what options are available in terms of sign shape, dimensions, and colours. We will also need to confirm where the sign will be positioned at the level crossing to understand how large the font size needs to be, and in turn, how many words or images are available to us for intervention design.
  • Sign permanence: We will need to confirm whether the sign can be easily removed during the trial to understand whether we are able to test multiple messages. If the sign cannot easily be removed, then we may only be able to test one message.
  • Outcome measure: We need to confirm what data air quality monitors collect and which of these measures are most important to reduce to improve air quality.
  • Comparator: We need to determine how we will define a comparator to measure the impact of our intervention. This could be done by comparing air quality of the same area before we put up the sign (a pre/post), by comparing air quality trends across similar areas (a difference-in-difference), or by putting up different signs at different times (a crossover design), among others.

[1] Monitors may also be installed at Mitcham level crossing. Merton is to confirm whether this level crossing is also in scope for the project.

[2] Air Quality Management Areas (AQMAs) Department for Environment, Food and Rural Affairs (Defra), Retrieved 18 August 2021, from

London Borough of Merton Air Quality Annual Status Report for 2020. (2021). LB of Merton.