Commute Cost Comparison Calculator

--- name: commute-cost-comparison-calculator description: Compares commute options - car (fuel or EV), transit, bike, e-bike, walking, day-share mixes and park-and-ride legs - per month and year with cash cost, door-to-door time, time cost at your own hourly value, cost per trip and CO2. Picks pass vs pay-per-ride for the days you ride, separates car running costs from fixed costs, and shows the break-even value of an hour. Includes a stdlib Python calculator with --self-test. --- # Commute Cost Comparison Calculator You help someone decide how to get to work by putting every option on the same footing: what it costs in cash, how much of their life it takes, and what that time is worth to them. You count what really changes with the choice (fuel, parking, fares, the bike), keep costs they pay anyway out unless they would actually sell the car, and show the trade-off as a clear number: "driving saves 32 lost hours a year and costs $3,697 more, so it pays only if your hour is worth more than $115". ## Files in this skill - `scripts/commute_cost.py` - reads a scenario JSON (distance, commute days, value of time, options) and prints a comparison table, headline, break-even values of time and per-option notes; supports metric (km, L/100 km) and imperial (mi, mpg), EVs, transit passes with daily caps and employer subsidies, day-share mixes and multi-leg trips (Python 3.8+ standard library only) - `references/cost-components.md` - every option field, what to include for each mode, where to find the numbers, and typical ranges - `references/time-value-and-assumptions.md` - how to choose a value of time, usable time on transit, what the totals leave out (health, safety, weather, flexibility) and how to run sensitivity checks - `templates/commute-comparison.md` - the decision summary to hand back - `examples/commute.json` - an 11-mile commute with driving, bus + light rail, an e-bike, an e-bike/transit mix and park-and-ride - `examples/comparison-output.md` - the real output of the calculator for that scenario ## Workflow ### 1. Collect the facts One-way distance, commute days per week (hybrid work matters a lot) and weeks worked per year, door-to-door minutes per option (including walking, waiting, parking and transfers: ask for a real trip, not the map estimate), and per mode: car fuel economy, fuel or electricity price, parking and tolls, whether they would keep the car anyway; transit fare, pass price, daily cap, employer subsidy; bike or e-bike price, expected life and upkeep. Ask what an hour of their time is worth, or offer a default (half their hourly pay) and show the sensitivity. ### 2. Run the calculator ``` python3 scripts/commute_cost.py examples/commute.json python3 scripts/commute_cost.py scenario.json --days-per-week 3 python3 scripts/commute_cost.py scenario.json --value-of-time 0 --json python3 scripts/commute_cost.py --self-test ``` Exit 0 = comparison printed, 2 = bad input (missing field, mix shares not adding up to 1, unknown mode, negative price). Without code, follow the formulas in `references/cost-components.md`. ### 3. Read the result - The table is sorted by total (cash + time cost); the headline names the cheapest in cash, the cheapest once time counts and the fastest. - **Break-even value of time** compares every option with the cheapest in cash: an option that costs more is worth it only if your hour is worth more than the number shown. "Never" means it costs more and does not save usable time. - Time spent on transit that you can use (reading, email) is discounted with `usable_time_share`; the same field can credit bike time that replaces exercise you would do anyway. Say which you used. - Check the transit note: on 2-3 commute days a week a monthly pass is often dearer than pay-per-ride; the calculator picks the cheaper and says so. ### 4. Deliver Fill `templates/commute-comparison.md`: recommendation in one sentence, the table, break-even values, what changes the answer (hybrid days, fuel price, parking, value of time), what is not priced, and a trial suggestion (e.g. two weeks of the mix before buying anything). ## Example result 11 miles each way, 5 days a week, 46 weeks, time valued at $20/hour (`examples/commute.json`). Cheapest in cash: bus + light rail at $49/month after a $50 employer subsidy (the $99 pass beats $105 of single fares). Cheapest once time counts: park and ride ($95 cash, $361/month total) because 80 % of the train leg is usable. Driving downtown is fastest (28 min) but costs $357/month with $12/day parking and pays off only if an hour is worth more than $115. The e-bike costs $67/month all-in and emits nothing, but it does not save usable time at these numbers; it wins if the ride replaces gym time. See `examples/comparison-output.md`. ## Rules - Count only costs that change with the choice; include car insurance, registration and loan costs only if the person would actually give up the car (`count_fixed`). - Use real door-to-door times, including walking, waiting, parking and transfers. - Never present the value of time as a fact: it is the person's own choice; show at least one sensitivity run (e.g. `--value-of-time 0` and their wage). - Keep health, safety and weather out of the money totals but mention them; do not moralize about cars or bikes. - State every assumption with its number (fuel price, parking, depreciation per mile) so the person can change it. - Give currency and units as the person uses them; do not mix miles and kilometres in one scenario.