# Road Transport Distance-Based Emission Factors – Calculation Note

## 1. Fuel-based per-litre emission factors

| Fuel   | Factor ID                               | Value (kgCO2e/L) | Primary source      | Additional sources           |
| ------ | --------------------------------------- | ----------------:| ------------------- | ---------------------------- |
| Petrol | `ng.transport.road.petrol.per_litre`    | 2.354            | IPCC 2006 Vol 2 Ch3 | DEFRA 2024, EPA GHG Hub 2024 |
| Diesel | `ng.transport.road.diesel.per_litre`    | 2.662            | IPCC 2006 Vol 2 Ch3 | DEFRA 2024, EPA GHG Hub 2024 |

Both are aligned with DEFRA 2024 100% mineral petrol/diesel factors and corroborated by IPCC 2006 default road-vehicle emission factors. GWP basis: AR5.

## 2. Distance-based derivation approach

Nigeria does not publish public vehicle-kilometre or test-cycle fuel-consumption data. Therefore the distance-based factors are **UK DEFRA 2024 per-km proxies**, used for Nigerian reporting only where activity data is available in kilometres.

For cars, motorcycle, van and HGV, the committed factor is the DEFRA 2024 per-km value rounded to three decimal places. The accompanying `vehicle_fuel_consumption_l_per_100km` values are **back-calculated reference values** and are shown only to make the relationship to the fuel-based EF explicit.

For the bus, DEFRA 2024 publishes a **passenger-km** factor. It is converted to vehicle-km using a NEFDB occupancy assumption.

## 3. Reference fuel-consumption values (for context)

| Vehicle type                               | Fuel    | L/100 km | Notes |
| ------------------------------------------ | ------- | --------:| ----- |
| Average petrol car                         | Petrol  | 6.954    | Back-calculated from DEFRA per-km factor and fuel-based EF |
| Average diesel car                         | Diesel  | 6.316    | Back-calculated from DEFRA per-km factor and fuel-based EF |
| Average motorbike                          | Petrol  | 4.805    | Back-calculated from DEFRA per-km factor and fuel-based EF |
| Local bus (urban bus, passenger-km basis)  | Diesel  | n/a      | Per-vehicle-km obtained from passenger-km × occupancy |
| Light commercial van (up to 3.5 t)         | Diesel  | 9.306    | Back-calculated from DEFRA per-km factor and fuel-based EF |
| Heavy goods vehicle                        | Diesel  | 32.464   | Back-calculated from DEFRA per-km factor and fuel-based EF |

## 4. Resulting distance-based factors

| Factor ID                                   | Vehicle type        | Fuel    | Source per-km value | Calculation                     | Value (kgCO2e/km) | Confidence | Uncertainty |
| ------------------------------------------- | ------------------- | ------- | -------------------:| ------------------------------- | -----------------:| ---------- | ----------- |
| `ng.transport.road.petrol.car`              | Passenger car       | Petrol  | 0.1645              | Direct DEFRA proxy              | 0.165             | medium     | 20%         |
| `ng.transport.road.diesel.car`              | Passenger car       | Diesel  | 0.16984             | Direct DEFRA proxy              | 0.170             | medium     | 20%         |
| `ng.transport.road.petrol.motorcycle`       | Motorcycle          | Petrol  | 0.11367             | Direct DEFRA proxy              | 0.114             | low        | 30%         |
| `ng.transport.road.diesel.bus`              | Urban bus           | Diesel  | 0.10846/passenger-km| 0.10846 × 30 passengers         | 3.254             | low        | 35%         |
| `ng.transport.road.diesel.truck.small`      | Light van           | Diesel  | 0.25023             | Direct DEFRA proxy              | 0.250             | medium     | 20%         |
| `ng.transport.road.diesel.truck.heavy`      | Heavy goods vehicle | Diesel  | 0.87296             | Direct DEFRA proxy              | 0.873             | medium     | 20%         |

## 5. World Bank 2013 annual-km defaults

The World Bank (2013) *Assessing Low-Carbon Development in Nigeria* provides Nigeria-specific annual-kilometre defaults from a 2010–2012 survey. These are **not used in the per-km factors** but are provided for users who have vehicle-stock data and need total annual emissions.

| Vehicle category                         | Annual km/vehicle | WB 2013 reference |
| ---------------------------------------- | -----------------:| ----------------- |
| Motorcycle / two-wheeler                 | 7,000             | Table 21.6        |
| Passenger car                            | 17,000            | Table 21.6        |
| Light commercial vehicle / danfo minibus | 30,000            | Table 21.6        |
| Urban bus                                | 30,000            | Table 21.6        |
| Long-distance coach                      | 45,000            | Table 21.6        |
| Heavy goods vehicle / truck              | 33,500            | Table 21.6        |

## 6. Confidence and uncertainty flags

- **High confidence** is only assigned to the fuel-based per-litre factors because they are corroborated by IPCC defaults and peer-government conversion-factor datasets.
- **Medium confidence** is assigned to car and van/HGV distance factors: the values are deterministic, but UK driving conditions differ from Nigerian conditions (traffic congestion, fuel quality, vehicle age/loading, road surface).
- **Low confidence** is assigned to the motorcycle and bus factors:
  - Motorcycle: very limited Nigeria-specific data; the DEFRA motorbike proxy may not correspond to Lagos/urban Nigerian motorcycle usage.
  - Bus: the conversion from passenger-km to vehicle-km using a 30-passenger occupancy is highly sensitive.

## 7. Bus occupancy sensitivity

If the actual average occupancy differs from 30 passengers, adjust the vehicle-km factor reciprocally:

```
vehicle_km_EF = passenger_km_EF × occupancy
```

Examples:
- 15 passengers: 0.10846 × 15 = 1.627 kgCO2e/km
- 30 passengers: 0.10846 × 30 = 3.254 kgCO2e/km
- 60 passengers: 0.10846 × 60 = 6.508 kgCO2e/km

Users measuring passenger-kilometres directly should prefer a passenger-km-based factor (not yet in NEFDB) and apply an observed occupancy.