Inside Our Emission Engine: How EcoFreight Turns a Route Into a Carbon Number

50 milliseconds. That's the budget my team set for a single POST /api/v1/calculate call — from raw origin string to a verified WTW emissions number with GLEC Framework v3.2 factor attribution. We hit p50 around 42 ms and p95 around 174 ms in production. Below is what fits inside that window. I am Mayur Rawte (background on the author page); I work on the calculation engine and I want this post to be the answer to "what exactly happens when I make one call against your REST API?"

The five steps below are the literal pipeline. Every box is code one of us shipped. When something is approximate, I have flagged it. When something is exact, I have flagged that too. If you came here to read a marketing piece, this is not it; if you came to understand what your auditor will be able to verify from the JSON response, read on.

Step 1: Geocoding

We resolve location names to coordinates using Mapbox geocoding. "Rotterdam" becomes [51.9225, 4.4792]. You can pass city names, full addresses, port codes (NLRTM), or airport codes (FRA) — we normalize everything to lat/lng pairs before moving on. The lookup is cached for 24 hours, so a repeat city name avoids the Mapbox round trip. Cache hit ratio sits around 91% across our top thousand origins and destinations, which is most of the latency budget recovered.

Step 2: Route Calculation

Distance calculation depends on the mode:

Step 3: Emission Factor Selection

We use GLEC Framework v3.2 default emission factors, published by the Smart Freight Centre and aligned with ISO 14083. The factor we select depends on four things:

• Transport mode — road, rail, sea, or air
• Vehicle/vessel type — a 3.5t van differs from a 40t articulated truck
• Fuel type — diesel, LNG, electric, etc.
• Boundary — WTW (well-to-wheel) or TTW (tank-to-wheel)

The selected factor is expressed in grams of CO2e per tonne-kilometer (g CO2e/tkm). The full factor table is downloadable from our methodology page with every value mapped back to its Smart Freight Centre source row, so an auditor can cross-walk a single response back to the input table without asking us for anything.

Step 4: The Calculation

Step 5: Data Quality Tier

ISO 14083 defines three data quality tiers:

What an auditor can verify from one response

The thing that surprised me most when I started shipping this engine was how often the auditor only needs the JSON. Once the response carries the methodology version, the factor source, a stable calculation_id, and the engine version that ran the math, almost every assurance question is answerable from the payload alone. Three things in particular survive the audit:

• Reproducibility. The same input today and in 2028 returns the same number, provided you pin factor_set: "glec_v3_2" on the request. When we ship a new factor table, old calculation_ids keep resolving against the original engine version — no silent recalculation.
• Attribution. The emission_factor field names the value, the unit, and the source ("GLEC Framework v3.2"). The auditor cross-walks back to the published Smart Freight Centre row without asking us for anything.
• Tier transparency. The response says which tier produced the number. A Tier 1 factor flagged as such is more defensible at audit than a Tier 3 claim that quietly degraded to Tier 1 because primary data was missing.

I wrote this engine because the closest competing implementations I had reviewed would not survive a CSRD assurance walk-through. The fields above are the ones I would want as the auditor on the other side of the table. For a longer take on the ecosystem and where each vendor places those fields differently, see the comparison post.

The API

// Request
{
  "origin": "Rotterdam, Netherlands",
  "destination": "Munich, Germany",
  "mode": "road",
  "weight": 12000
}

// Response
{
  "emissions": {
    "wtw": 617.5,
    "ttw": 524.9,
    "wtt": 92.6,
    "unit": "kgCO2e"
  },
  "distance_km": 830,
  "emission_factor": {
    "value": 62.0,
    "unit": "gCO2e/tkm",
    "source": "GLEC Framework v3.2"
  }
}

Honest Limitations