Wh/Passenger-mile

[Ben W]

I've been thinking... if the Model S had sensors in all seats, then it would be able to track Wh/passenger-mile (in addition to standard Wh/mi). This, I think, would be a much more meaningful real-world statistic, and would make consumers much more vividly aware of the efficiency benefits of carpooling.

For instance, driving solo, I typically average about 340 Wh/mi. Imagine if the dashboard were to display ~170Wh/p-mi when you're traveling with a passenger! (or 70Wh/p-mi, with four passengers!)

For hypermilers, or anyone who cares about their driving efficiency and environmental impact, I think this could go a long way. It's sobering to think that hypermiling at 35MPH solo with the A/C off, is no better (in Wh/p-mi) than a double-occupancy car cruising 80MPH with the A/C blasting. By the same metric, a fully occupied Range Rover is just as fuel-efficient as a solo-driven Model S. Food for thought.

With 34k miles on my Model S, my lifetime trip meter shows 352 Wh/mi. I'd guess that my average passenger-aware efficiency is around 250 Wh/p-mi. (In other words, average occupancy of about 1.3 people.) But this is entirely speculative. I'd be curious to know the actual number.

Thoughts? Would you like it if Tesla did this? If you like, post your lifetime Wh/mi, and take a guess at your lifetime Wh/p-mi. It may be instructive.

 

[jerry33]

Additional passengers don't affect the Wh/mi all that much and I'm pretty sure that most people are concerned with the total, not with the per-passenger, energy use because that is what affects range and the total cost of running the car. All this would really tell anyone is that a full bus is more efficient than a car, which everyone already knows.

Lifetime 248 Wh/mi. Per passenger 200 Wh/mi. I don't see how that's instructive though as it doesn't help me go further on a charge or provide any useful information that could be used to adjust driving style.

 

[Chipper]

These stats might be somewhat misleading if one drives far more conservatively when the significant other is in the car.

 

[Ben W]

Additional passengers don't affect the Wh/mi all that much

If you're thinking of it in terms of the total environmental impact for a given group to go on a given journey, it certainly does. If five people are traveling from City A to City B, and they drive separately (in Teslas), the Wh/mi for the entire group would be around ~1750Wh/mi. If they share a ride, the total is only ~350 Wh/mi. That's a huge difference.

I'm pretty sure that most people are concerned with the total, not with the per-passenger, energy use because that is what affects range and the total cost of running the car.

Yes, and that's looking at it the wrong way. If you find ways to occasionally ride in someone else's car, then those passenger-miles are effectively "free" to you. (In terms of your own costs.) Conversely, if you take a passenger, the miles are effectively free to them. The more people do this, it adds up to significantly lower total costs all around. Focusing solely on your own car's Wh/mi does not align nearly as well with your total transportation costs, taking "free rides" with others into account.

All this would really tell anyone is that a full bus is more efficient than a car, which everyone already knows.

People know this abstractly, but bringing it to the front of one's awareness on a daily basis is a powerful thing. It's why houses with "smart meters" quickly become far more efficient, because people are made more immediately aware of how their behavior (turning off lights, etc.) impacts efficiency.

Really, it can be thought of as a form of 'gamification'. When presented with a concrete score, particularly if it's shown relative to your peers, you're much more likely to try to optimize it. In terms of Tesla's ultimate goal, which is to reduce global environmental impact and improve energy conservation, optimizing for Wh/passenger-mile is much more meaningful than optimizing for Wh/mile. Humans naturally like to optimize, so it's highly important to choose the "scoring" system that aligns best with these ultimate goals.

Lifetime 248 Wh/mi. Per passenger 200 Wh/mi. I don't see how that's instructive though as it doesn't help me go further on a charge or provide any useful information that could be used to adjust driving style.

If it makes you more conscious of the benefits of carpooling, (e.g. that two people sharing a car will be 10x more beneficial to the environment than making a "hypermiling"-style optimization), then that's instructive. The point is that "driving style" techniques are seriously overrated as a way to conserve energy and total costs, relative to carpooling.

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These stats might be somewhat misleading if one drives far more conservatively when the significant other is in the car.

Not really. In terms of Wh/passsenger-mile, conservative driving alone may save ~10%, but riding with two people instead of one saves 50%. (vs. taking two cars.) That's really the point that needs to be made.

 

[jcaspar]

Can't you just divide your Wh/mile by the number of passengers? Pretty simple math. I would be interesting to see the Wh/mi for a family with 5 kids in a Model S, or would the system only divide for the number of licensed drivers in the car??

I agree the benefits of carpooling in a electric vehicle are much less obvious that in an ICE vehicle where you clearly see your savings each time you fill up.

 

[Ben W]

Can't you just divide your Wh/mile by the number of passengers? Pretty simple math. I would be interesting to see the Wh/mi for a family with 5 kids in a Model S, or would the system only divide for the number of licensed drivers in the car??

It's simple math for a single trip, but the car can keep cumulative track over time, which would be an onerous bookkeeping task for a human. Lots (perhaps most) drivers never reset their "B" trip, so they preserve a record of the average efficiency for the lifetime of the car. It can become a game to try to improve this efficiency over time. (It has for me, and I consider myself only a very mild hypermiler.) If Wh/p-mi were tracked, then people who were trying to improve that efficiency (it's "just a game", but people like games) would be rewarded each time they carpool.

I agree the benefits of carpooling in a electric vehicle are much less obvious that in an ICE vehicle where you clearly see your savings each time you fill up.

Interesting point. It's also true that, say, carpooling in one hummer vs. driving a fleet of hummers would yield a much larger absolute savings than the Tesla equivalent (i.e., one Tesla vs. multiple Teslas). And there's no reason that such a feature shouldn't work just as well on ICE cars. Keeping track of lifetime passenger-miles per gallon (or even better, gallons per 100 passenger-miles) would be a just as effective and meaningful measure.

 

[jerry33]

If it makes you more conscious of the benefits of carpooling

Carpooling sounds nice as a hypothetical practice, but in the real world where you often stay late, come in early, or get called back after you get home it's not particularly practical. It also adds another hour to your commute as you pick up and drop off the other three people--and if one of them has been smoking before--just yuck.

 

[Ben W]

Carpooling sounds nice as a hypothetical practice, but in the real world where you often stay late, come in early, or get called back after you get home it's not particularly practical. It also adds another hour to your commute as you pick up and drop off the other three people--and if one of them has been smoking before--just yuck.

Well, yes. If only everybody would just stop smoking... and my car has the signature white interior, too...

Certainly it's unrealistic to expect a massive change. But a nudge in that direction, even if it only helps 1%, is still 1%. Tesla engineers wracked their brains for months trying to reduce the drag coefficient by 1%. Adding a couple cheap seat sensors seems like a no-brainer.