> For the complete documentation index, see [llms.txt](https://docs-integration.squake.earth/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs-integration.squake.earth/notable-changes/calculation-changes/train-rem-v2-7.md).

# Train: REM methodology v2.7

We’ve updated SQUAKE’s Rail Emissions Model (REM) to **version 2.7**. This release refreshes and expands the verified rail emission factor dataset across all five REM tiers, updates train-type and detour-factor coverage, and improves consistency across REM calculations.

## What's New?

### Updated Tier 1–5 Emission Factors

REM v2.7 introduces updated and re-validated emission factors across **Tier 1 through Tier 5**, including refreshed operator-specific, country- and service-specific, and fallback values.

The dataset also expands validated operator and country coverage. As a result, the most specific factor resolved for a rail journey may differ from the previous REM version.

### Expanded Train-Type Coverage

REM now supports the expanded set of canonical train types available in the latest dataset, including categories such as `commuter` and `urban_rail` where applicable.

This allows REM to use more specific factors when they are available instead of falling back solely because a train type was not previously supported.

### Updated Detour Factors

Detour factors used to estimate rail-route distance have been updated and expanded.

These factors are applied only when SQUAKE needs to estimate rail-route distance from straight-line origin/destination distance. They are not applied when an actual rail-route distance or passenger-kilometre value is already available.

Because of this update, calculations where the rail distance needs to be estimated may change compared with earlier REM versions.

### Fallback Logic Remains Unchanged

The REM fallback hierarchy remains:

**Tier 1 → Tier 2 → Tier 3 → Tier 4 → Tier 5**

REM continues to use the most specific verified factor available for the provided journey data. It does not create a synthetic `average` factor from a specific train or service type when a verified average is unavailable.

Tier 4 remains country-specific, while Tier 5 continues to provide the global fallback.

## What This Means for You

No change is required to existing integrations that already use the SQUAKE train methodology.

However, recalculating the same rail journey with REM v2.7 may produce a different result where:

* an emission factor has been updated or corrected;
* new operator or country coverage provides a more specific factor;
* expanded train-type coverage changes factor resolution; or
* an updated detour factor is used to estimate rail-route distance.

For more information about the Rail Emissions Model, see the [SQUAKE Rail Emissions Model whitepaper](https://www.squake.earth/resources/rail-emission-model-whitepaper).