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Why are my taxi-related emissions so high vs. last year or other categories? 

Taxi emissions are a common source of confusion. Large year on year changes or unusually high values are usually driven by the emissions factor used rather than a real change in travel behaviour. Below is a simple explanation of why this happens and how to interpret your results.

The short answer

  • Taxi emissions factors vary widely by country, data source, and calculation method.

  • Spend based taxi factors can differ by more than 10 to 20 times depending on assumptions.

  • Changes in factors between years can significantly affect results even if spend is similar.

  • Trace uses a reputable Australian spend based factor by default, but this can be adjusted if needed.

Why taxi emissions factors can vary so widely

1. Spend based vs distance based approaches

  • Spend based factors calculate emissions per dollar spent.

  • Distance based factors calculate emissions per kilometre travelled.

  • Spend based taxi emissions factors are one of the most variable categories in Scope 3. This is not a data quality issue. It is a result of how these factors are constructed and the assumptions built into them. 

2. Country specific differences

  • Average taxi fares differ by country and city.

  • Vehicle fleets differ in fuel type, efficiency, and utilisation.

  • Electricity grid intensity affects electric and hybrid vehicles differently by region.

For example:

  • New Zealand taxi spend factors are much lower partly due to different fare structures and data assumptions.

  • Australian taxi spend factors are higher when using national economic input output data.

3. Scope of what the emissions factor covers

Not all taxi emissions factors represent the same activity. Many spend based factors labelled as taxi or taxi and hire car actually cover a wide range of services, such as:

  • Taxis

  • Chauffeur and ride with driver services

  • Hire cars with drivers

  • Passenger vehicle hire not elsewhere classified

  • In some datasets, buses and coaches with drivers

Because these factors average emissions across multiple transport services, they are often higher than factors designed specifically for taxis only. This explains why narrow taxi only datasets, such as some New Zealand sources, produce much lower values, whereas broader economic sector factors used in Australia or international input output models are materially higher.

You are not comparing like for like when the underlying service definition is different.

5. Price, fare, and exchange rate effects

Spend based factors sometimes rely on converting emissions per kilometre into emissions per dollar. This requires several assumptions and small differences in these assumptions compound quickly. Key drivers include:

  • Average taxi fare per kilometre

  • Urban vs regional driving assumptions

  • Fuel efficiency and vehicle mix

  • Currency exchange rates

For example:

  • A 10 percent change in exchange rates can directly change emissions per dollar by 10 percent.

  • Differences between NZD and AUD taxi fares can add another 10 to 20 percent variation.

  • Emissions per kilometre assumptions can vary by up to 100 percent depending on the source.

As a result a value like 0.045 kg CO2e per NZD can reasonably translate to closer to 0.1 kg CO2e per AUD once local prices and assumptions are applied.

6. Basic price vs purchaser price application

Spend based factors typically have 2 options: Basic price vs Purchaser price. For more information on Basic vs Purchaser price factors and which Trace uses, please read this article.

For most goods and services purchaser price includes margins such as tax, freight, and transport. Purchaser price emissions factors work well because those margins represent real upstream activity.

For transport services themselves, such as taxis the service is the margin so using purchaser price can inflate emissions because taxes and margins are layered onto a service that already represents transport activity.

Using basic prices changes this:

  • Basic price reallocates the full economic value back to the transport sector itself.

  • This better reflects the direct emissions intensity of the taxi service.

  • For taxi and hire car categories, basic price factors are often around half of purchaser price factors.

This is why:

  • For most categories, purchaser price factors are lower than basic price factors.

  • For transport categories, the opposite is often true, which can feel counterintuitive.

Examples of how much taxi factors can differ

Below are examples of taxi emissions factors expressed as kg CO2e per Unit.

Spend factors

  • Australia 2024 release purchaser price: 1.52 kgCO2e / AUD (Footprint Lab)
  • Australia 2025 release - purchaser price: 1.77 kgCO2e / AUD (Footprint Lab)
  • Australia 2025 release - basic price: 0.88 kgCO2e / AUD (Footprint Lab) - Trace uses this one
  • New Zealand 2024 release: 0.0454 kgCO2e / NZD (New Zealand Gov - Table 22)

  • Australia 2025 data - spend converted to distance: 0.06 - 0.16 kg CO2e / AUD depending on $ / km (VIC EPA analysis - page 16)

Distance Factors

  • New Zealand 2024 release: 0.160 kgCO2e/km (New Zealand Gov - Table 22)

  • Australia 2025 release - light vehicle:  0.1908 kgCO2e/km (NTC 2025)

  • UK 2025 release - ave car, unknown fuel type: 0.16725 kgCO2e/km (DEFRA 2025)

This illustrates how the same taxi spend can produce very different emissions results depending on the source and calculation approach.

Why your taxi emissions may have increased year on year

Your taxi emissions may be higher due to one or more of the following:

  • Updated emissions factors released by data providers.

  • A change in factor methodology rather than actual travel.

  • A shift from older or lower international benchmarks to Australian specific data.

  • Reclassification within broader transport or hire car categories.

This is normal and expected in carbon inventories.

How Trace selects Taxi Emissions Factors

  • Trace uses spend based emissions factors from Footprint Lab as the primary source for Australian data. For more information on this source, read this article. These factors are based on environmentally extended input output analysis and reflect Australian economic activity.

  • Factors are updated as new releases become available.

Can emissions factors be changed?

Yes, emissions factors can be changed, but we recommend doing so only where there is a strong methodological reason.

Trace prioritises methodological robustness and consistency over selecting the lowest available factor. Using a stable approach year on year supports clearer trend analysis, easier explanations, and stronger audit outcomes.

We generally do not recommend changing factors simply to reduce emissions, as this can:

  • Undermine year on year comparability

  • Create apparent changes that are not driven by real activity

  • Make internal and external communications more difficult

There are situations where adjusting factors is appropriate, such as moving from spend based to activity based data, improving geographic relevance, or meeting assurance or regulatory requirements. Any change should be clearly justified and documented, and ideally applied consistently across reporting periods.

If you would like to explore options for adjusting emissions factors, get in touch with the Trace team at Support@our-trace.com and we can help you assess the implications before making any changes.