Post #1310: What does 30 electrical miles get you?

Posted on October 29, 2021


We haven’t bought gasoline since mid-August, owing to my wife’s purchase of a Prius Prime.  That’s a plug-in (PHEV) version of the Prius, with a battery that’s good for about 30 miles.

It’s not like we stumbled into that purchase.  We researched the offerings available and decided that hit the sweet spot for us.  No range anxiety, no need to rewire the garage, and no need to mortgage the house if that big battery wears out.

And, as you can guess, it’s working out well.  We’re not avoiding traveling, it’s just that most of what we do seems to fit into that 30-mile-a-day limit.  Or nearly.

Which got me to wondering: Is our experience all that unusual?

I mean, people seen to think that little 30-mile battery isn’t much.  It’s certainly no Tesla, either for distance or acceleration, for sure.  But it’s not intended to be, and, from my perspective, that smaller battery is efficient.  Most people who drive a full EV aren’t going to use the full capacity of their battery on most days.

But with this PHEV setup — where the first 30 miles is electric, then it switches to gas — just how much gas would the average American save?

More precisely, how much would total U.S. private passenger vehicle gasoline consumption decline if the first 30 miles of everybody’s driving day were done on electricity?  As if everybody had a Prius Prime, but nobody could recharge mid-day.  And with no change in behavior otherwise.

Turns out that you can’t just look that up.

You can find some glib statistics on (e.g.) the fraction of individual car trips that are short.  And yeah, sure, most car trips are for just a few miles.  I don’t think anybody’s shocked by that. But that’s not the question.

So I turned to the National Household Travel Survey (NHTS) to get an answer.  If you ever want to know anything about how Americans get from A to B, that’s the place to look.

I took their file of vehicle trips, reduced it to travel by private passenger vehicle (car, SUV, van, pickup), focused on the vehicle driver only (to avoid duplicating drivers and passengers), and summed up the total miles that each driver drove, each driving day.   That yielded about 150,000 distinct person-days of vehicle driving.  At that point, I (arithmetically) substituted up to 30 miles of that with electricity, and tabulated the results.

Source:  Calculated from 2017 NHTS trip file, weighted estimate.

And there’s your answer.  If you were to substitute the first 30 miles of everybody’s private vehicle driving-day with electrical transport, you’d reduce gasoline-powered miles by 55%.  That’s all the miles on days under 30 miles, and 41 percent of the miles on days over 30 miles.

The upshot is that with PHEV, that 30-mile battery is enough to cut average private-vehicle gasoline consumption more than in half.  All of that, without the truly huge batteries required for full EVs.  And without a whole new electrical infrastructure required to keep EVs going, at least for those of us who can recharge at home out of a standard wall socket.

So I’m back to where I ended up in my last post about electrical transport.  People seem to get all caught up in their underwear about this huge, dramatic, risky blah-blah-blah.

And it’s all nonsense.  If you have a standard outlet available, you have the option to shift most of your personal transportation to electricity.  Right now.  With absolutely no other change in your lifestyle.  And a Federal tax credit, to boot, depending on what you choose.

Well, OK, in truth, we have made a few lifestyle changes.  I buy fewer lottery tickets now.  But that’s probably a good thing.  Otherwise, except for remembering to plug it in, there’s no practical difference between our last (all-gas) car, and our current (nearly-all-electric) car.

And now, judging from the U.S. numbers, we’re probably not alone in terms of the advantages from that small PHEV battery.

Think of it as a case of diminishing returns.  Your first few miles of electric capability get the most bang-for-the-battery-buck.  Here’s the picture, same data source and analysis above, just plotted for PHEV batteries of various sizes.

Source:  Calculated from 2017 NHTS trip file, weighted estimate.

Sure, you can be a purist and insist on nothing but electrical travel.  And more power to you.  But even with zero change in behavior, and no mid-day charging, a PHEV with a modest battery size can get you a long way toward that goal.