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Revised 19 October 2026 · v1.0.0 · what changed

Code: github.com/herrrickshaw/vehicle_fuel_mileage

Watch the walkthrough

Watch on YouTube: youtu.be/TLlSUbHjzAM

Why it is useful

• Car buyers, fleet managers and students can compare running costs across fuels with editable inputs instead of trusting a headline claim: choose a city, change the E20 mileage drop or usage, and the whole workbook reprices.
• It replaces hand-built comparison spreadsheets with an auditable one: formula-driven, with 21 automated checks, and mileage assumptions calibrated on 303 real declarations rather than guesses.
• Evidence from the run: 19 tests passed, the workbook built in 0.1 s, LibreOffice recalculation reported 0 errors, and the Checks sheet read ALL PASS.
• The same data showed the E20 effect on an average petrol car: 16.67 kmpl falls to about 16.0 kmpl at a 4% drop.

What it is for

vehicle_fuel_mileage builds an 11-sheet Excel cost model (cities, cost per km, ethanol impact, total cost of ownership, tax structure, fleet sales, OMC price board, exchequer revenue) on a July 2026 price basis, plus a Word report builder and a script that extracts and analyses fuel-efficiency declarations from the SIAM PDF.

This post covers the model workbook and the declaration analysis. Prices are inputs in the workbook: update them to today's before drawing conclusions.

Who it is for

• Vehicle buyers comparing petrol, diesel, CNG and EV running cost
• Students and analysts studying fuel taxation and ethanol blending
• Developers who want a worked example of a tested, formula-driven Excel build

What you need

Get the code and an AI assistant

You do not have to be a programmer. Get the repository, give it to an AI assistant, and ask in plain language. Any of these routes works:

git clone https://github.com/herrrickshaw/vehicle_fuel_mileage.git
cd vehicle_fuel_mileage
claude      # or: gemini

Install

1. Clone and enter the repo

   git clone https://github.com/herrrickshaw/vehicle_fuel_mileage.git
   cd vehicle_fuel_mileage

2. Create a virtual environment and install dependencies

   python3 -m venv .venv && source .venv/bin/activate
   pip install -r requirements-dev.txt

Quick start: commands and what you should see

Run the tests

python -m pytest -q

19 passed in about 1.5 seconds.

Analyse the 303 fuel-efficiency declarations

python scripts/analyze_fe_declarations.py

A fuel-type summary table, the petrol-to-CNG uplift, and the E20 mileage haircut.

Build the Excel model, then recalculate it

python scripts/build_model.py
python scripts/recalc.py outputs/EV_CNG_Diesel_Ethanol_Vehicle_Cost_Model.xlsx

A saved workbook with 11 sheets, then JSON reporting status success and 0 errors. Open the CostPerKm sheet.

Sample outputs

Real output from a run on the date shown in the sources line; trimmed to fit.

Fuel-efficiency declarations by fuel type (analyze_fe_declarations.py, run 19 Oct 2026)

python scripts/analyze_fe_declarations.py
Gasoline         n=188  mean FE  16.67  mean CO2 152.2
Diesel           n= 95  mean FE  17.91  mean CO2 153.6
CNG              n= 11  mean FE  27.40  mean CO2 102.1
Gasoline Hybrid  n=  8  mean FE  21.94  mean CO2 116.6

Same-model petrol->CNG mean distance uplift: +40.3%  (11 nameplates)
Mean petrol declared FE 16.67 kmpl -> E20@4% 16.0 kmpl (-0.67)

Fuel efficiency is km per litre (petrol, diesel), km per kg (CNG). Hybrid and electric rows are small samples.

Cost per km, Delhi prices (CostPerKm sheet after recalculation, Rs per km)

open the CostPerKm sheet
Vehicle        Petrol(E20)  Diesel  CNG   EV
Hatchback      6.65         -       2.97  1.41
Sedan          7.09         4.33    3.20  1.51
Compact SUV    8.18         5.01    3.78  1.63
Two-wheeler    1.93         -       0.81  0.35

Inputs: petrol Rs 102.12/L, diesel Rs 95.20/L, CNG Rs 83.09/kg, electricity Rs 10.6/kWh blended

Petrol cost already includes the selected 4% E20 mileage drop.

Hatchback cost per km across six cities (Cities sheet, Rs per km)

open the Cities sheet
City       Petrol  CNG   EV
Delhi      6.65    2.97  1.41
Mumbai     7.24    3.07  1.73
Kolkata    7.39    3.34  1.52
Chennai    7.02    3.46  1.41
Bengaluru  7.27    3.46  1.52
Hyderabad  7.53    3.46  1.57

Diesel per km is shown in the sheet for the compact SUV only.

Built-in consistency checks

open the Checks sheet
21 individual checks, all PASS
Overall: ALL PASS

Read after LibreOffice recalculation reported total_errors: 0.

Ways to use it

Sample prompts for your AI assistant

Copy, paste and edit the parts in [brackets].

• Explain this repository in plain English: what does the Excel model compare and where do its mileage numbers come from?
• Run the tests and the declaration analysis, then summarise petrol, diesel and CNG efficiency in a small table.
• Update the Delhi petrol, diesel and CNG prices in the model to [current prices] and tell me which fuel is cheapest per km for a hatchback.
• How many km a year would I need to drive for an EV [price premium in rupees] to pay back versus a petrol car? Use the TCO_Scenarios logic.
• Read data/sources.md and list which assumptions are sourced and which are estimates.

Limits and honest caveats

Sources: the vehicle_fuel_mileage README, scripts and tests; pytest, analyze_fe_declarations.py, build_model.py and recalc.py run on 19 October 2026 on a fresh clone.

About this article: Researched, written and edited by Umashankar Triplicane Dwarakanathan, with AI research assistance; every figure is meant to trace to the primary source cited. See the Editorial Policy for how sourcing, AI use and corrections work.