The Behavioural Economics of Vehicular Idling

Participants are randomly assigned to one of six groups (N = 6,000 total) in an eight-week intervention designed to reduce excessive vehicle idling. The study combines personalised behavioural messaging, financial incentives, and a low-cost technological reminder. The six groups are:

Private Information (1,000): Drivers receive personalised weekly messages about the private costs of idling, including wasted fuel and engine wear.
Private + Social Information (1,000): In addition to private cost messages, drivers are shown the broader social costs of idling, including air pollution and climate change impacts.
Private + Social Information + Payment (1,000): This group receives the combined messaging plus a monetary incentive for reducing excessive idling, based on GPS-tracked reductions relative to baseline. The payments are designed to elicit drivers’ willingness to accept (WTA) anti-idling behaviour.
Private + Social Information + Tech (2,000 total):
a. IdleGuard (990): Receives combined messaging plus an in-vehicle beeping device that emits an audio alert when the vehicle idles for more than 30 seconds.
b. Tech Control (990): Receives the same combined messaging but no device. This group serves as a comparison for the IdleGuard arm.
Pure Control (1,000): Receives no messages or device.

All messages are delivered weekly via WhatsApp, email, and a mobile app. Excessive idling is tracked using GPS data and defined as a continuous engine-on spell lasting more than 30 seconds.

2025-11-21

2026-01-21

• Idling-related outcomes
• Fuel expenditure
• Emissions
• Other driving behaviour outcomes

Idling-related outcomes include excessive idling duration, mean idling duration, and episode count per week, measured via GPS. Fuel expenditure is based on weekly self-reported fuel use. Emissions are estimated using standard conversion factors applied to reductions in idling. Other driving behaviour outcomes include GPS-derived indicators such as engine runtime and trip frequency.

• Beliefs about idling
• Willingness to accept (WTA) incentives
• Long-run idling behaviour
• Uptake and response to the audio reminder device

Beliefs are measured at baseline and endline, covering perceptions of fuel use, engine wear, and pollution impacts. WTA is estimated from choices and behaviour in the incentive arms. Long-run idling behaviour is assessed a few months after treatment using GPS data. Uptake and behavioural response to the audio device are analysed within the tech treatment group.

The unit of randomisation is the vehicle. A total of 6,000 private vehicles are randomly assigned to one of six groups in a 6-arm individual-level RCT. Randomisation is stratified by baseline idling behaviour. Treatments are delivered over an eight-week period. Idling outcomes are measured using continuous GPS data provided by a vehicle tracking system. Survey outcomes are collected via phone-based baseline and endline surveys. Weekly fuel data are collected via WhatsApp.

Not available

Randomisation done in office by a computer, stratified by baseline idling behaviour.

Individual vehicle (driver); all treatments are randomised at the individual level.

No

6,000 vehicles (drivers)

6,000 vehicles (drivers)

1,000 vehicles control
1,000 vehicles private info
1,000 vehicles private + social info
1,000 vehicles private + social info + payment
990 vehicles private + social info + payment + IdleGuard
990 vehicles private + social info + payment + Tech Control

The minimum detectable effect size (MDE) for excessive idling duration (minutes per week) is 1.46 minutes, equivalent to 0.083 standard deviations or 5.8% of the trimmed sample mean. This estimate is based on analytical power calculations with covariate adjustment (baseline idling, vehicle age), trimming of the top 5% of idlers, and a 3.8% attrition adjustment. The calculations assume 80% power and 5% significance, with an effective sample size of 1,924 drivers (from an initial 2,000 in the two comparison groups).