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New action

Remove the roof box between uses

An unused roof box adds aerodynamic drag.

I commit
Miniature scene: An empty roof box stays fitted.
An empty roof box stays fitted
Miniature scene: Store the box until its next use.
Store the box until its next use
01 / Why this can help

Your scenario, drawn

The same route, with or without the box

The same route, with or without the boxUnused box fitted: 210 L fuel; Box removed: 195 L fuel; Annual difference: -15 litres of fuel usedIN ONE YEARUnused box fitted210 L fuelBox removed195 L fuel0210 L fuel

Same scale, starting at zero. Change the assumptions to compare the two annual totals.

Sources and scope →
Read the values
Unused box fitted210 L fuel
Box removed195 L fuel
Annual difference-15 litres of fuel used
02 / One possible next step

When the roof box is no longer needed, follow its removal instructions and store it safely; arrange help if lifting requires it.

03 / Sources and scope

Context-dependent outcome

What the evidence supports

An unused roof box adds aerodynamic drag. Removing it can reduce the energy needed for the same driving, with the size of the saving depending on the vehicle, box and route.

Boundary of the claim

Box shape, speed, wind and the mounting system all affect the result. Only count kilometres when the box would otherwise remain fitted unnecessarily; remove and store it according to its instructions.

What this simulation calculates

The 7.0 and 6.5 L/100 km rates and 3,000 km distance are hypothetical examples, not values measured in the cited study. For a vehicle-specific estimate, use comparable existing records or necessary trips; do not add driving just to measure. A single dashboard reading does not establish causation.

Published coefficients and calculation references

  • Official guidance and a two-vehicle experiment support the aerodynamic mechanism. Published fuel-economy percentages are not applied here; litres per distance and distance per litre are different ratios. The paper was checked through its abstract and metadata only.

    Driving More Efficiently ↗

  1. Institutional guidance · U.S. Department of Energy and U.S. Environmental Protection Agency; website administered by Oak Ridge National Laboratory

    Driving More Efficiently

    Consulted section (original language): Avoid Hauling Cargo on Your Roof; View Data Sources reference 5

    Consultation: Webpage / full text

  2. Research study · John Thomas; Shean Huff; Brian West (Oak Ridge National Laboratory) · 2014

    Fuel Economy and Emissions Effects of Low Tire Pressure, Open Windows, Roof Top and Hitch-Mounted Cargo, and Trailer

    Consulted section (original language): Publisher abstract, first paragraph

    Consultation: abstract and publisher metadata · DOI: 10.4271/2014-01-1614

  3. Institutional guidance · UK Vehicle Certification Agency · 2025

    Fuel efficient driving tips

    Consulted section (original language): Remove roof boxes, rack etc. when not in use

    Consultation: Webpage / full text

Avoid counting the same change twice

Sources reviewed:

Report a data issue

Other possibilities in this area

Getting around
Miniature scene: The same trip by bicycle.Take the bike for a short tripMiniature scene: Use the stairs when feasible.Take the stairs when you canMiniature scene: Share one car for that journey.Share a regular journey
universalizable.Getting around / 01

Remove the roof box between uses

Miniature scene: An empty roof box stays fitted. Miniature scene: Store the box until its next use.
An empty roof box stays fittedStore the box until its next use

Why this can help

An unused roof box adds aerodynamic drag. Removing it can reduce the energy needed for the same driving, with the size of the saving depending on the vehicle, box and route.

One possible next step

When the roof box is no longer needed, follow its removal instructions and store it safely; arrange help if lifting requires it.

What changes the outcome

Box shape, speed, wind and the mounting system all affect the result. Only count kilometres when the box would otherwise remain fitted unnecessarily; remove and store it according to its instructions.

universalizable.The action / 02

Your illustrative scenario

Over one year · with the assumptions below

You

15 litres of fuel used less

You + 10 friends

165 litres of fuel used less

1,000 participants

15,000 litres of fuel used less

These are scenarios, not measured personal or collective savings. One separate vehicle per participant. A shared car is counted once.

Your inputs

Fuel rate with the unused box
7 L/100 km
Fuel rate without the box
6.5 L/100 km
Annual kilometres when the box is unnecessary
3,000 km

Calculation of the difference: (7 − 6.5) L/100 km × 3000 km / 100 = 15 litres of fuel used

Calculation boundaries

Fuel used by the same combustion-engine car on comparable necessary journeys. Match route, speed, traffic, wind, engine temperature, payload and tyres. The difference cannot be attributed to the box if these also change. Count only kilometres still driven after other travel changes. No electric-car or carbon conversion.

The 7.0 and 6.5 L/100 km rates and 3,000 km distance are hypothetical examples, not values measured in the cited study. For a vehicle-specific estimate, use comparable existing records or necessary trips; do not add driving just to measure. A single dashboard reading does not establish causation.

Sources and calculation references

  1. Driving More EfficientlyU.S. Department of Energy and U.S. Environmental Protection Agency; website administered by Oak Ridge National Laboratory
  2. Fuel Economy and Emissions Effects of Low Tire Pressure, Open Windows, Roof Top and Hitch-Mounted Cargo, and TrailerJohn Thomas; Shean Huff; Brian West (Oak Ridge National Laboratory) · 2014
  3. Fuel efficient driving tipsUK Vehicle Certification Agency · 2025

Read the method: universalizable.com/en/method/ · One sheet · print double-sided, long-edge binding

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