TEI 5.1 builds directly on the ideas behind TEI 5.0 but makes the underlying logic clearer and more people‑centred.

Rethinking Car Efficiency

How TEI 5.1 evolves TEI 5.0
TEI 5.0 already combined weight, power, seats, aerodynamics and energy use into one efficiency score. TEI 5.1 keeps the same ingredients but rearranges them around a simpler question: how much energy and material are we using to move one person, and how much extra weight and power are we adding on top of that?

How does TEI 5.1 work?

TEI 5.0 treated efficiency as a sum of different penalties for weight, power, drag, energy use and (for EVs) battery mass. TEI 5.1 keeps these same technical ideas, but organises them around a single core quantity: the energy and material needed to move one potential passenger 100 km. On top of this base, it adds clear penalties for unnecessary mass, size, drag and power, so that the final 0–100 score reflects how well a vehicle uses resources to do the simple job of transporting people.

The TEI 5.1 formula considers several key vehicle characteristics:

  •  Weight (kg): Still the main driver of energy use and material impact.
  • Seats: Used to spread energy and material cost over potential passengers.
  • Horsepower: Now treated explicitly as “power per seat”, so excess performance per person is penalised.
  • Tire width (cm): Continues to represent rolling resistance and space taken on the road.
  • Cd (Drag Coefficient): Still captures aerodynamic efficiency.
  • Energy consumption: The same WLTP / EPA figures as before, but now clearly positioned as the starting point of the calculation.

These factors are weighted and combined to create a single score that represents overall transportation efficiency.

Conceptual TEI 5.1 formula

TEI 5.0 combined several terms into a single additive index.

TEI 5.1 keeps that spirit but makes the structure explicit:

1.Start from energy per potential passenger
- energy_per_seat
= energy_consumption / seats
← energy needed to move one person 100 km

2.Add penalties for waste, using the same vehicle properties as TEI 5.0
- mass_per_seat_penalty
← extra weight per seat compared to a light reference vehicle
- aero_and_tire_penalty
← Cd × tire width per seat, capturing aerodynamic and rolling losses
- power_per_seat_penalty
← excess horsepower per seat beyond what is sufficient for everyday use
- battery_oversize_penalty
← applied only to EVs with large batteries, reflecting extra material and weight

3.Convert this into a 0–100 score, as in TEI 5.0
- TEI 5.1 score
= 100 weighted_penalties(
energy_per_seat,
mass_per_seat_penalty,
aero_and_tire_penalty,
power_per_seat_penalty,
battery_oversize_penalty
)
The weighting constants are chosen in the same way as TEI 5.0: real vehicles end up between 0 and 100, with genuinely small and efficient designs near the top and oversized, overpowered vehicles near the bottom.

TEI 5.0 already used a 0–100 scale. TEI 5.1 keeps the same bands so existing scores remain comparable, but the story behind them is now easier to understand:

  • 80-100: Exceptional efficiency
    Vehicles that use very little energy per seat and avoid unnecessary weight and power. This includes the most efficient microcars and carefully designed compact vehicles.
  • 60-79: Very good efficiency
    Cars that are still relatively light and modestly powered, with reasonable aerodynamics and energy use per seat.
  • 40-59: Average efficiency
    Typical modern cars. They move people, but carry more mass, drag and power per person than is strictly necessary.
  • 20-39: Below average efficiency
    Heavy, wide or strongly powered vehicles that consume a lot of energy and materials per passenger.
  • 0-19: Poor efficiency
    Extremely heavy or overpowered vehicles whose design choices are far removed from the simple task of moving people efficiently.

TEI 5.1 keeps the familiar TEI 5.0 inputs and 0–100 scale, but refocuses everything on “energy and resources per passenger” .

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