Parasitic Energy Ratio is a simple metric for comparing the relative energy wasted by various modes of transportation.
PER = Stop-Starts in traffic/stations x Vehicle Mass per passenger / Payload Mass (mass of a person)
Parasitic Energy Ratio (PER) Calculations (with stops for traffic/stations between origin and destination)
| Mode | Start-Stops | Vehicle Mass per Passenger (kg) | PER Calculation | PER Value | Wh/passenger-mile |
|---|---|---|---|---|---|
| Car | 10 | 1,300 | (10×1300)/90 | 144.4 | 1032 |
| Bus | 10 | 1,167 | (10×1167)/90 | 129.7 | 1245 |
| Light Rail | 10 | 1,633 | (10×1633)/90 | 181.4 | 818 |
| Bike | 5 | 20 | (5×20)/90 | 1.1 | 25 |
| JPods | 1 | 250 | (1×250)/90 | 2.8 | 78 |
Key Observations: Efficiency vs. Liberty
- Efficiency (PER):
- Bikes (PER = 1.1) and JPods (PER = 2.8) are 100–50x more efficient than cars (PER = 144.4).
- Light Rail (PER = 181.4) is the least efficient due to high mass and frequent stops, despite moving many passengers.
- Cars waste energy accelerating/stopping 1,300 kg of vehicle mass per passenger vs. 90 kg of payload.
- Liberty and On-Demand Service:
- Cars dominate US trips (92%) because they prioritize physical liberty: door-to-door, on-demand travel.
- Mass transit (5% of trips) sacrifices liberty for efficiency, requiring riders to comply with schedules and fixed routes.
- Bikes/JPods balance both: bikes offer freedom but limited range; JPods (grade-separated, non-stop) promise liberty and efficiency but require infrastructure investment.
- Policy Failures:
- US policies favor cars (e.g., subsidized highways, parking mandates), forcing 92% of trips into high-PER modes.
- Greenwashing Risk: Promoting buses (PER = 129.7) and light rail (PER = 181.4) as “sustainable” ignores its inefficiency and lack of liberty.
Implications for Climate and Quality of Life
- Short Trips Matter:
- 80% of US trips are <10 miles, making bikes/JPods viable for most needs.
- Yet only 4% of trips use bikes/walking due to car-centric infrastructure.
- Value = Efficiency + Quality of Service:
- Cars score poorly on efficiency but high on liberty.
- Bikes/JPods score high on both but are marginalized by policy.
- Mass transit scores poorly on liberty and inconsistently on efficiency.
- Solutions:
- Prioritize Low-PER Modes: Invest in bike lanes, micromobility, and automated JPods for short trips.
- Reform Subsidies: Redirect car-centric funding to liberty-preserving, low-mass systems.
- Liberty-Centric Metrics: Use PER to expose greenwashing (e.g., heavy rail/buses marketed as “green” despite high energy waste).
Summary
- PER exposes trade-offs: High liberty (cars) = high energy waste; low liberty (mass transit) = mixed efficiency.
- Bikes/JPods are the “sweet spot” for short trips, but policy stifles adoption.
- Recommendation: Shift incentives to reward systems that simultaneously optimize PER and liberty (e.g., on-demand, lightweight transit).
Personalize the consequences of Parasicit Mass Ratio
Steps to put this metric in personal terms:
- Park your car in your driveway empty of gasoline.
- Put in one gallon into your tank.
- Get 5 of your strongest friends (watt-hours per persons).
- Drive until you run out of gas.
- Push your car home. If you can keep your car rolling at 2 mph, it will take you 12.5 hours to push it home.
Framework
Run your own Parasitic Energy Ratio calculations. Here is a starting framework:
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Parasitic Energy Ratio is a metric to compare relative wasted energy moving vehicle mass for various transportation modes. Parasitic Energy Ratio equals Start-Stops time Vehicle Mass per passenger divided by Payload Mass (person).
Background issues:
- Mobility is physical liberty to go where we want, when we want to take advantage of events and places that supports earning a living and enjoying life.
- Government efforts to coerce people to comply with schedules of mass transit ignores the loss of value of individual liberty and results in low service levels except when large numbers of people can be coerced to comply with schedules.
- PER is intended to mitigate the risks of “greenwashing”, public policies that are intended to address climate risks while actually increasing the risks.
Please calculate PER in the US for a Car, Bus, Light Rail, Bike, and JPods vehicle:
- If you cannot find the vehicle mass per passenger, here are default values: Bus, 1167; Light Rail, 1633; Car, 1300; bike, 20, JPods 250.
- Use these values for the number of Start-Stops at stations and stop signs: Bus, Light Rail, and car 10; bike 5 (bike riders often adjust speeds to avoid stopping at lights); JPods 1 (grade-separation provides origin to destination, non-stop trips)
- Mass of the person at 90 kg (~200 pounds)
In addition to calculate values, please summarize the importance of liberty and personal, on-demand service. Value is a combination of efficiency and quality of service. Unless you find data to the contrary, 80% of trips in the US are less than 10 miles, US policies force 92% of trips to be by car, 4% by walking or bikes, and 5% by mass transit.
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