Post #1624: 80 MPG?

 

Not quite.  But I think I’m finally figuring out how to drive my wife’s Prius Prime.

Above is the gas mileage on my wife’s Prius Prime, after a round trip from Vienna VA to Harper’s Ferry WV.  This is all after resetting the odometer once the battery was depleted.  So it’s straight-up gas mileage.

This trip contained a short section of high-speed driving, but was mostly hilly primary and secondary roads in western Virginia and West Virginia.  And I think I finally understand how I’m getting such great mileage.

The Prius Prime loves hilly roads.  It is an excellent car for a particular style of pulse-and-glide driving.

Continue reading Post #1624: 80 MPG?

Post 1621: Look ma, no battery!

 

Or, “why I truly don’t give a 💩 about high gasoline prices in the U.S.”, the sequel.

Back in June of this year, in Post #1454, I explained why I didn’t give a 💩 about the price of gas.  In a nutshell, I don’t use much.  I drive my wife’s Prius Prime.  The 30-mile battery range covers essentially all our local travel.  One we’ve run through that, the gas mileage is outstanding.

The genesis of the prior post was our annual trip to Ocean City, Maryland, where the car got 72 MPG on the highway.

I figured it was a fluke.  There were no hills to speak of.  We probably caught a tailwind.  Unlikely to be repeated.

Today we went leaf-peeping, driving from Vienna VA to Sperryville, VA and back.  There is just something about the autumn scenery in central Virginia that my wife and I both love.

(Best sign seen on the trip:  “God Allows U-Turns”.  This, at the exit of the parking lot of a little church in Sperryville where we were — yeah — making a U-turn.)

The trip was a combination of interstate highways, then primary and secondary highways traversing hilly terrain. It was a nice drive — once we got off the interstate.  I reset the odometer after the battery was depleted so that I could check the gas mileage.

Lo and behold, in round numbers, 72 MPG.  Straight-up gasoline-powered transport, no battery.  Completely different terrain, time of year, and driving conditions compared to last time.

So, no fluke.  I’m not drafting trucks. I’m not doing 35 in the right-hand lane.  I’m  just keeping up with traffic, and paying a bit of attention to instrumentation on the dashboard that offers guidance for best fuel economy.  (And it didn’t hurt that we didn’t need AC or heat for this trip.)

It’s odd how your expectations change.  These days, if I come in under 65 MPG for the gas portion of a trip, I’m disappointed.

This is not as clean as a pure EV of the same size.  At least, not as clean, at Virginia’s current electrical generating mix.  But it’s not bad for the latest refinement of a gasoline-based technology that Toyota put on the road more than two decades ago.  And the same drive train that gets us 72 on the highway allows us an effortless transition to electrical transport for all our around-town driving.

For us, this plug-in hybrid electric vehicle (PHEV) is absolutely the sweet spot in the spectrum of what’s on the market today.  After a year of driving this car, we have no regrets about buying it.

Post #1620: Musings on putting together a bug-out bag

 

This is a lengthy set of ramblings.  There's a conclusions section at the bottom if you just want the bottom line.

I continue in my quest to Get Rid of Stuff, a.k.a., Swedish Death Cleaning.  At present I’m wondering what to do with four decades’ worth of camping gear.  Most of it is lightweight gear for backpacking.  My answer is to repurpose it into a couple of bug-out bags (or SHTF bags).

For those unfamiliar with the term, a bug-out bag is set of emergency supplies packaged so you can easily pick it up and carry it away.  Typically, it’s a backpack full of stuff.

Many responsible entities suggest that every citizen have one of these on hand.  You can get guidance on what ought to be in a typical bug-out bag from, among others, FEMA, the CDC, the Red Cross, the U.S. Army, the Commonwealth of Virginia, and Fairfax County, VA.  I’m emphasizing that because having a bug-out-bag or emergency kit isn’t something you should associate with end-times preppers.  It’s a completely prudent thing to have and maintain.

Though I have to admit that all the loose talk about nuclear war and dirty bombs does not exactly reduce my anxiety level, given that we live about 15 miles from the Pentagon.  Plus, all the anti-democracy craziness at play in the coming elections suggests a non-negligible chance I might end up on the wrong side of a armed mob.  And then there’s always the odds of the next Carrington Event.  Which, while maybe not quite as destructive as an electromagnetic pulse (EMP) from a high-altitude nuclear explosion, could wreck the power grid, with all that implies for ensuing long-term lack of water, food, fuel, and commerce in general.  But let’s keep it mainstream.  Think blizzard, hurricane, or similar natural disaster.

To be clear, for almost any conceivable emergency, I’m going to shelter in place.  We’re never going to get hurricane-force winds this far inland.  I’m never going to have to go on the lam to avoid arrest.  And in the event of nuclear war, the last place I want to be is in a multi-day traffic jam on I-66.  I’m going to stay where I have a comfortable bed and flush toilets.

At-home preparedness really isn’t the issue.  Almost everyone who lives in a big suburban house pretty much has that covered.  E.g., every person with a standard hot water heater is already storing 50 gallons of potable water.  For us, with a modern wood stove and a car that serves as an electrical generator (see Post #1020), we’ve got heat and light.  We’d suffer no hardships to speak of in (e.g.) a prolonged winter power outage.

When you step back from it, the question isn’t what to put in a bug-out bag. You can get lists of suggestions anywhere.  Heck, you can buy them ready-made on Amazon.  The basics are pretty obvious:  Water, food, shelter, light, sanitation, medicines.  And batteries.  Lots and lots of batteries.  It’s just another version of going camping.

The key question is why have a bug-out bag?  Given that I have all the basics of existence covered at home, why would I even want something I can pick up and carry off?

Let me defer an answer to that for the moment.  Because if you carry through on that thinking, you will immediately arrive at an even more basic question for which — around here at least — there is absolutely one correct answer. To get oriented, all I really need to ask myself is this:  What am I most likely to be facing, if I’m picking up those bug-out bags and heading out of town?

Around here, the answer is obvious.


Scenario 1:  Three-day traffic jam.

Northern Virginia is pretty much one big traffic jam on the best of weekdays.  If there is some general reason to evacuate this area, by far the most likely result will be a multi-day traffic jam.  Similar to — possibly worse than — the Houston evacuation prior to hurricane Rita, or the Florida state-wide traffic jam for the evacuation for hurricane Irma.

Once I started looking into that, it seems that more-or-less every modern mass evacuation in the U.S. has generated horrific traffic jams. So an epic traffic jam isn’t just likely, it’s more-or-less guaranteed in any large-scale emergency evacuation situation in the U.S.  No matter what the underlying reason, if a lot of people around here suddenly decide to go elsewhere, a massive traffic jam will be the inevitable result.

In addition, recall the earlier this year, a snowstorm broke I-95 in central Virginia, leaving people trapped in their cars, in the middle of nowhere, in the snow, in central Virginia, for more than 24 hours (reference).  My point being that you don’t necessarily even need a mass evacuation to find yourself trapped in your car for a day or more.

Accordingly, the first thing I really ought to prepare for, in a set of bug-out-bags, is spending a few days in the car.


A typical evacuation traffic jam.

Traffic jam, Florida, Hurricane Irma.  Source:  Accuweather (AP Photo/Gerald Herbert).

Let me briefly see what I can learn from recent U.S. hurricane evacuation experiences.

Here’s one first-hand account.  Some takeaways:

  • Stores were still open, so if traffic was stopped, you could hop out and use the restroom at local commercial establishments.  Plausibly, you may or may not need a porta-potty or urinal in the car, depending on whether traffic is literally stopped.
  • Once the traffic jam got started, it snowballed due to people running out of gas.
  • That then littered the road and shoulder with stopped cars, which made access for emergency equipment far more difficult.

Here’s a good scholarly article on traffic and hurricane evacuations.

  • Basically, nobody does anything to manage or stage the traffic load.  In most modern instances, while evacuation routes are identified ahead of time, once the evacuation starts, it’s just every man for himself, with the resulting chaos.
  • Roads rapidly fill past the optimum point on the K-Q curve  — the point of greatest throughput — and that throttles down the number of vehicles able to leave an area.
  • This due, in large part, because everybody waits until the last possible moment.
    • Elected officials, hoping that (e.g.) the hurricane will go elsewhere.
    • Residents, ditto
  • If I get one takeaway from that, it’s that if you are going to evacuate, do it as early as possible.

One other takeaway from that one is that people spend a lot of time farting around as they prepare to evacuate.  That adds to the chaos and further slows traffic.  They don’t have a plan, they need to hit the stores for supplies and so on.  They don’t even have a preferred route.  That strongly suggests having a preferred evacuation route in mind, and having your supplies ready to go.

Here’s a weird little tidbit, from this analysis of Florida evacuations for hurricane Irma.  So many people chose Orlando as their destination that you didn’t just have traffic jams on the gulf coast, you ended up with massive traffic jams around Orlando.  The authors described the results as “catastrophic traffic jams throughout the state”.   The clear takeaway there is to avoid what you believe will be the most common destination for people leaving your area.  In fact, the Irma evacuation caused massive traffic jams in Atlanta, Georgia.  I can only guess that was mostly people who couldn’t get a hotel room in Orlando.

This scholarly analysis adds another helpful hint.  When everybody in an area goes out to gas up the car and pick up bottled water, hey, guess what happens?  Gas and water get scarce.  The clear implication there is that you should consider keeping supplies of both water and gasoline on hand.  If nothing else, you won’t be adding to the chaos in the run-up to the evacuation.  (Although, admittedly, stockpiling a bit of gasoline involves some risks and difficulties.)

For my part, given that the Prius Prime has a 640-mile range at the stated EPA mileage, and that traffic jams actually increase your mileage, my guess is that all I would need is a full tank.  I can’t imagine the scenario where I’d have to run more than 700 miles.  I mean, I’m only 400 miles from Niagara Falls, so that range gets me well up into Canada.  So I shouldn’t need to take gas cans in the car.  Just have enough on hand to be sure to be able to fill the tank.

It almost goes without saying that you are unlikely to be able to obtain a hotel room during a mass-evacuation scenario.  Just to put some numbers on that, in all of Florida, there are under 500,000 hotel rooms (reference).  On any given day, two-thirds of them are already occupied (same reference).  On a good day, for the entire state, you might have 150,000 empty rooms.  The Irma evacuation in Florida involved an estimated 4 million vehicles (reference).  In round numbers, for the entire state of Florida, there was at best one empty hotel room for every 25 evacuating vehicles.  So I’d say, plan for some alternative accommodation is good advice.  Barring that, book well in advance.

Floridadisaster.org puts it a bit more mildly:  ” … hotels and other sheltering options in most inland metropolitan areas are likely to be filled very quickly …”   So, in addition to urging you to leave sooner rather than later, they suggest that you identify someplace safe nearby, ” … minimize the distance over which you must travel in order to reach your intended shelter location. ”  All of that seems like sound advice.

The most important takeaway from that is the idea that you will have already identified your intended shelter location.  If you do it right, you aren’t just evacuating the area, you’re evacuating to a chosen destination.

I have not seen any advice or empirical evidence on whether or not it would be better to use secondary routes rather than interstates or primary highways.  In some places — and Florida comes to mind there — the only through roads are the primary highways and interstates.  But in other areas, you might have a fairly well-developed network of secondary routes.


So what I really need is an instant #vanlife kit?

Yeah, pretty much.  That’s my conclusion, anyway.  No matter what the emergency, if there’s a mass evacuation in this area, we’re all going to be living in our cars for a day or two.

In addition to what you’d put in a normal bug-out bag (water, food, light source, and so on), I should ideally have three more things on hand, ready to go, in case of an emergency evacuation.

Source:  Clipart library.com

First, pre-select a handful of potential destinations, at various distances, and store that list in the car.  Apparently, during many of out recent hurricane-driven evacuations, a lot of people wasted a lot of time trying to figure out where they could go.  This hesitation pretty much guarantees getting stuck in the worst of traffic. Even if you’ve picked a (one) place, there’s going to be a pretty good chance that there will be (e.g.) no hotel rooms or camping spots left.  So pick several.

As I would almost certainly be driving west, and have no relatives living west of me, that would almost certainly be a list of hotels and campgrounds along the interstate and primary highways leading west of here.  Write it down and keep that list in the car.

Source:  Amazon.com

Second, keep some gasoline on hand.  A second clear lesson is that any situation that would generate a mass evacuation will also generate panic-buying of gasoline.  And if there’s anything we learned from COVID, it’s that panic buying can clear out the local inventories in a flash.  In my case, I’d want enough to ensure that I could fill the tank of my wife’s car — about ten gallons.

This is a lot tougher to do well, because gas goes “stale” in a relatively short amount of time, perhaps as little as three months.  This is due largely to the loss of the most volatile components.  As they evaporate, it raises the flash point of what’s left and makes it harder for a spark plug to ignite it.

The upshot is that you have to rotate your stock.  You can’t just put some filled gas cans on a shelf and be done with it.  You need to transfer that stored gas to your car periodically and re-fill you gas cans with fresh gas.

Maintaining adequate gasoline turnover is already a minor issue for some PHEV owners.  If you do almost all your driving on battery, you might keep the same gas in your tank for a prolonged period.  That said, car fuel systems are sealed, so there’s relatively little evaporation.  I believe Toyota recommends at least half a tank of fresh gas every year.

Just by chance, I actually have the right equipment for storing modest amounts of gasoline.  That’s a gasketed metal jerry can, as pictured above.  Those have no vent, and they seal completely when closed, slowing the rate at which the gas goes bad.  I can’t recall exactly how I came to own mine, but I’m sure they can no longer be sold in CARB-compliant areas such as the DC metro area.

I’m undecided as to whether I’m going to store a can or two of gas.  The decision to store gasoline is a commit to the effort it takes to keep it fresh.  I’m not sure it’s worth the effort.

At this point, I think I have the inputs for this process down pat. 

My final concern is for outputs.

What are your alternatives if you’re stuck in the car and can’t get access to a bathroom?  I realize you can stop the car, run into the woods, and take care of business in some fashion.  The interesting question is, what can you do without getting out of the car?

And, in the modern era, well, of course there are multiple websites that will tell you just exactly how to poop and pee in the car.  Typically with some variety of D-I-Y receptacle.  And numerous vendors of commercial products for the same purpose.   And the inevitable YouTube videos.

After working through a considerable amount of that, I’ve decided to do two things.

One, I’m going to buy a pack of the “Travel Jane” brand disposable urinals above.  These contain a polymer that gels more-or-less instantly when it comes in contact with urine.  Apparently the shape is more-or-less female-friendly (but guys can use it too.)

Enough said about #1.

And then there are the various contraptions for an in-car #2.  Of which, none of them look like they’ll work for a fat guy in a Prius.  (And a standard steel bedpan won’t work, because it slopes the wrong way to be used in an already-sloping car seat.)  Instead, I’ll be cutting down a five-gallon-bucket-style emergency toilet, to match the dimensions needed to work with a car seat (3″ front, 5″ rear).

Then buying a box of disposable liners.

Then hope like hell I never have to use the thing.  And that’s that.


Some commentary on disaster kit checklists

There’s no point in my offering you a list of stuff to go into your own bug-out bag or disaster kit.  There’s no shortage of experts who will tell you what to keep on hand for disaster preparedness.  By and large, they all say the same things.  And those are pretty obvious:  Water, food, shelter, sanitation supplies, and so on.  I listed some references at the start of this post.

I will add just four refinements that you may not read elsewhere.  These are all about maintaining that emergency kit once you have put it together.

First, never leave the batteries in your devices.  Take them out, and put them in a plastic bag taped to the device.  Although battery corrosion is far less of a problem now than it was decades ago, alkaline batteries will eventually corrode.  And you’ll only find out that the device is ruined when it ceases to function.

Two, invest in a cheap battery tester.  Five dollars will get you a perfectly adequate tester on Amazon.  That will pay you back in terms of batteries that you don’t have to throw away, because they remain within spec even after sitting around for a few years.

Three, separate out all the items that need to be replaced periodically, and put them all in their own bag.  Food, medications, batteries, and so on.  Anything that has an expiration date.  If not, you’ll have to go rooting around in your kit, every year, to check for expired items.  Which means you won’t bother to do it.  Which means that when you go to use your bug-out bag, it will be full of expired items.

Four, use a sharpie to mark the purchase date of every food item.  And every other item that is in your bag of expire-ables.  This takes almost no time, and saves you having to squint at the various packages when checking the contents of your bug-out bag.

In terms of the standard lists of items, oddly, almost all of these lists not only have the same items, they have the same handful of items that I consider to be decades out-of-date.

Some common bits of bad advice

Surely the most out-of-date recommendation found on every list is to carry some travelers’ checks.  Travelers’ Checks?  Do they even make those any more?  (Answer:  Yes, American Express still offers Travelers’ Checks.)  I cannot imagine the situation in which cash would not be superior to Travelers’ Checks.

In the same vein, there’s a suggestion that you carry some change, in addition to paper money.  Maybe there are still vending machines that don’t require electricity and don’t take bills.  I can’t recall having seen one for a long time.  My guess is, that’s a recommendation that dates back to the era of pay phones.  Otherwise, if I’m in a situation, the last thing on my mind will be worrying about having to round up to the next whole dollar.

Arguably, the second most out-of-date recommendation is to carry matches in a waterproof container.  Don’t.  Carry a Bic lighter.  (What the heck, go crazy, carry two.)  Backpackers made that switch decades ago.  Bic advertises 3000 lights from its full-sized model, and most people seem to get a lot more than that.  And it’s inherently waterproof.  I can’t even imagine carrying 3000 matches.

Third worst recommendation is to include a bottle of bleach.  This was to be used to sanitize clear (non-cloudy) water for drinking.  But that’s a bad recommendation for a couple of reasons.

First, household bleach degrades rapidly.  Unless you are prepared to replace that every couple of years (or annually, per most sources), you’ll have no idea what strength the bleach is.  Standard household bleach is either 6% or 8.5% sodium hypochlorite.  Accordingly, use 8 or 6 drops of bleach per gallon of clean, pre-filtered water.  This, per the U.S. EPA.  In round numbers, to be safe, that’s a quarter-tablespoon per gallon of clear water.  Stir and let stand 30 minutes.

But that’s also a bad recommendation for drinking water purification because the technology has improved.  Back in the day, you had your pick of awkward ways to disinfect water.  Boil the water for one minute, or use water purification tablets (foul tasting and only partially effective), or use bleach (merely foul tasting).  There were also systems set up around the use of iodine rather than chlorine.

These days you have many better options.  There are microfiltration systems, such as the Lifestraw or higher-volume units that use (more-or-less) dialysis filtration material to filter pathogens out of the water.  There are systems that use salt and electricity to create chlorine for water disinfection.  There are systems that use battery-powered UV-C lights to disinfect water.  And so on.

For my part, I’m tossing one of the little Sawyer micro-filtration water filters into each bug-out bag.  Plus a handful of coffee filters for pre-treatment.  If I ever get to the point where I’ve run out of potable water, that’s going to be a lot more reliable than whatever happens to be left in an N-year-old bottle of household bleach.

Some good advice that I wouldn’t have thought of.

By contrast, here are some things I wouldn’t have thought to add:

A lot of lists recommend keeping a complete change of clothes in your emergency kit.  I guess, in the back of my mind, I figured I’d also pack a suitcase.  But if this really is for an emergency getaway, maybe a change of clothes in the bug-out bag is a good idea.  Particularly if you are making some sort of kit to reside in your car.

I would not have thought to include maps of my area.  But that makes perfect sense, as you could easily imagine a situation in which the cell towers are out.  Of course, if I’m traveling by car, I’ll have a set of maps already.

A final general item that I would not have included on my own is a selection of standard over-the-counter medications.  Things like antacids, anti-diarrhea medications, and so on.  I could see where (e.g.) a bad case of acid reflux or heartburn could be a real hindrance if you couldn’t get your hands on some antacids.

Otherwise, those lists are pretty much all the same.  And pretty much common sense if you have any camping experience.


A brief diversion on the space blanket.

Source:  Walmart

Everybody tells you to pack a space blanket.  Few people have ever tried (e.g.) camping with just a space blanket, nothing else.  (I have, and it doesn’t do much to keep you warm.)  Virtually nobody understands how space blankets actually work.  Yet that lack of understanding does not keep people from offering advice on how to use them.  As a result, much of the advice you will get about space blankets is wrong.

A space blanket is, first and foremost, a radiant barrier.  Without even attempting to get into the physics of it, I’m just going to tell you the rules.  It only stops radiant heat if there’s at least a 1″ air gap on at least one side.  It doesn’t matter which side — which kind of belies the use of the word “reflect”.  All that matters is that at least one side faces at least a 1″ air gap.

Ignore that rule, and it’s just a cheap, thin piece of plastic.

If you put one of these under your sleeping bag, it does nothing to reflect heat.  If you drape a regular blanket over it, it does next-to-nothing to reflect heat.  (It only reflects heat in the spots where there’s an air space under it.)

If you’re going to use one of these, put on whatever insulation you are going to use — warm clothes, blankets, and so on — and drape the space blanket over that.  So that that the entire top surface of the space blanket is open to the air.

Think of it as the (shiny) icing on the cake.  That’s how to use it properly.

Now you know.


Conclusions

It has been a long strange trip from “what do I do with my old backpacking gear?” to “how, exactly, does one poop in a car?”.  Let me summarize.

Every U.S. entity that is responsible for emergency management suggests that you maintain some emergency supplies, including but not limited to some form of a bug-out bag.  Something so that, no matter what the chaos is surrounding some unexpected evacuation, you’ll have some basic elements of water, food, light and shelter with you.

Practically speaking, if you are part of some mass evacuation in the U.S., you will be driving your car or other vehicle.  Along with absolutely everybody else.  In a major evacuation the odds appear overwhelming that you are going to be caught in a massive traffic jam.  You will likely end up spending 24 hours or so — maybe more — in your car.  That’s not some one-off mistake.  That’s not some rare occurrence.  That’s seems to happen, like clockwork, with each major American evacuation event.  And if history is any guide, nobody is going to be doing anything to (e.g.) make that go more smoothly, enforce traffic laws, and similar.  Chaos appears to be more the rule than the exception in U.S. evacuation traffic jams.

Plan accordingly.

First, decided on your likely destinations ahead of time.  Have a paper-copy list with (e.g.) address and phone of hotels and campgrounds along your likely evacuation route.  The less time you spend dithering, the earlier you get on the road, and the more likely you can escape the worst of the traffic.  The absolute standard advice is that if you think you may need to evacuate, leave as soon as possible.  The less time spent gathering supplies and pondering your destination, the better.

A lesson from Hurricane Irma in Florida is:  Don’t choose the same destination as everybody else.  If there’s an obvious place to get a hotel room (e.g., in Florida, Orlando), go somewhere else.  Otherwise you get caught in a second major traffic jam at your destination.

Second, don’t assume that you’ll be able to get a hotel room.  Even in tourist-rich Florida, evacuees outnumbered available hotel rooms about 25-to-1.  That surely requires having several potential destinations in mind, and booking early.

Third, keep some gasoline on hand, if you can.  Because gas and bottled water are the first two things to run out when an evacuation is declared.  Gas, in particular, is tricky, because it goes bad.  You need to store it in an unvented container and you need to replace it periodically.

Fourth, include some way to take care of all your needs in the car.  Inputs and outputs.  From shopping Amazon, it’s clear that there are many effective and moderately-priced products that will handle urine.  But poop seems to be a different story entirely.  Most of the devices sold for that would either require a lot of empty floor space in your vehicle, or would require you to stop and get out of your car. A standard bedpan is the wrong shape for use in a car seat — tall at the front, short at the back.  For my part, I’m going to cobble up something from a five-gallon-bucket-style emergency toilet, and then hope that I never have to use it.

Beyond that, you can get reasonably good lists of what to include or not in a bug-out bag from any number of sources.  Or simply buy a ready-made kit from Amazon.  I have nothing to add to those other than the handful of minor refinements listed above.

In summary, the real eye-opener to me was the auto-centric focus you need for your personal planning.  If you’re not going to shelter in place, and you live in the typical urban American setting, then evacuation means getting to your shelter by car.  For most of us, any evacuation event means that we’re going to get a brief taste of #vanlife.  And I judge that most advice for constructing your bug-out bag pays little to no attention to that basic fact.

Post #1619, COVID-19, still at 12 new cases per 100K per day

 

We’ve definitely hit a plateau in daily new cases.   We’ve approaching three weeks at 12 new COVID-19 case / 100K / day.  There’s a little uptick in the Mountain states (Colorado and New Mexico).

But so far, in terms of a U.S. winter wave, that’s it.

Elsewhere, there’s no uptick in Canada.  And Europe still looks like it has passed the peak of its winter wave.  No upticks in Japan or South Korea.

No winter wave anywhere in the northern hemisphere, to speak of.

Graphs follow.

Continue reading Post #1619, COVID-19, still at 12 new cases per 100K per day

Post #1618: There ain’t no disputin’ Sir Isaac Newton: Efficient driving in an EV.


Driving an electric vehicle (EV) efficiently is forcing me to learn some new driving habits.  And, in particular, I have to un-learn some cherished techniques used for driving a gas-powered car efficiently.

When I look for advice on driving an EV efficiently, all I get is a rehash of standard advice for driving a gas car.  But the more I ponder it, and the more I pay attention to the instrumentation on my wife’s Prius Prime, the more I’m convinced that’s basically wrong.

An electric motor is fundamentally different from a gas engine.  With an electric motor, you want to avoid turning your electricity into heat, rather than motion.  That boils down to avoiding “ohmic heating”, also known as I-squared-R losses.

To minimize those heating losses, you want to accomplish any given task using or generating constant power.  That task might be getting up to speed after stopping at a red light, or coming to a stop for a red light, in some given length of roadway.

Here’s the weird thing.  Assuming I have that right — assuming that an efficient EV driving style focuses on providing or generating constant power over the course of an acceleration or deceleration — that implies a completely different driving style, compared to what is recommended for efficient driving of a gas-powered vehicle.

In particular, the standard advice for gas cars boils down to accelerating and decelerating with constant force.  When you take off from a stop light, aim for a constant moderate rate of acceleration.  When you are coming to a stop, aim for a steady rate of deceleration.  Constant acceleration or deceleration boils down to constant force on the wheels, courtesy of Sir Isaac Newton’s F = MA (force is mass times acceleration).

But power is not force.  As I show briefly, in the next section.  In a car, power depends on speed.  Constant force on the brake pedal (and so, on the brake rotors in a traditional car) generates far more power at high speed than at low speed.  Similarly, a constant rate of acceleration consumes more power at high speed than at low speed.

And so, there seems to be a fundamental conflict between the way I was taught to drive a gas car efficiently, and what seems to be the right way to drive an EV efficiently.

In a nutshell, to drive an EV efficiently, you should be more of a lead-footed driver at low speeds.  And taper off as the car speeds up.   Conversely, hit the brakes lightly at high speed.  And press the brakes harder as the car slows.

That’s the driving style that aims for production and consumption of power at a constant rate, over the length of each acceleration or deceleration. And that’s completely contrary to the way I was taught to drive a gas vehicle.

Think of it this way.  Suppose you apply a certain level of force to the brake pedal of a traditional car.  The resulting friction between brake pads and rotors will generate heat.  That rate of heat production is, by definition, power, as physicists define it.  You’re going to generate a lot more heat per second at 80 MPH than you are at 4 MPH.  (In fact, 20 times as much.)  Restated, for a given level of force, you are bleeding a lot more power off the car’s momentum at 80 MPH than at 4 MPH.  And those big differences in power, over the course of an acceleration or deceleration, are exactly what you want to avoid in an EV with regenerative braking, in order to avoid I-squared-R losses.

 


Force and power:  A brief bit of physics and algebra

1:  Two definitions or laws of physics

Work = Force x Distance

Power = Work/Time

2:  A bit of algebra

Substitute for the definition of work:

Power = (Force x Distance) / Time.

Re-arrange the terms:

Power = Force x (Distance/Time)

Distance/time = speed (definition)

Power = Force x speed.

For a constant level of force applied to or removed from the wheels, the rate of power consumption (or production) is proportional to the speed.

Upshot:  To accelerate or decelerate at constant power, the slower you are going, the heavier your foot should be.  The faster your are going, the lighter your foot should be.  For the gas pedal and the brake pedal.


Ohmic heating:  Why a long, hard acceleration trashes your battery reserve.

Anyone who drives a PHEV — with a relatively small battery — will eventually notice that one long, hard acceleration will consume a big chunk of your battery capacity.  On a drive where you might lose one percent of battery charge every few minutes, you can knock several percent off in ten seconds if you floor it.

Another way to say that is that getting from A to B by flooring it, then coasting, consumes much more electricity than just gradually getting the car up to speed.

I’m not exactly sure why that is.  But I am sure that it is universally attributed to I-squared-R or ohmic heating losses in the motors, batteries, and cables.

Any time you pass electric current through a wire or other substance, it heats it up.  From the standpoint of moving your car, that heating is a loss of efficiency.  The more current you pass, the more it heats up the wire.  And that heating is non-linear.  Watts of heat loss are proportional to I-squared-R, in the argot.  They go up with the square of the current that you pass through that wire.

Again, I’m not completely sure here, but my takeaway is that your heating losses, at very high power, are hugely disproportionate to your losses at low power.  At constant voltage, I believe those losses increase with the square of the power being produced by the electric motors.  In other words, ten times the power produced to move the car creates 100 times the ohmic heating losses.

And that’s how ten seconds of pedal-to-the-metal can use up as much electricity as 10 minutes of moderate driving.

That said, I have to admit that I’m relying on “what everybody says” for this.  For sure, hard acceleration seems to trash your battery capacity far in excess of the distance that you travel at that rate of acceleration.   Whether the root cause for that is I-squared-R losses, or something else about the car, I couldn’t say.

Either way, my takeaway is that if losses are proportional to the square of power consumed or generated, then to accomplish any given task (any fixed acceleration or deceleration episode), your aim should be to do that at constant power.  Because that’s what will minimize the overall energy loss from that acceleration or deceleration episode.


Drive like you are pressing on an egg — that was a real thing.  EV drivers should chuck the egg.

Source:  Duke University Libraries, via Internet Archive.

Those of us who grew up during the 1970s Energy Crisis will probably recall public service announcements that asked you to drive as if there were a raw egg between your foot and the gas pedal.  I managed to find a Texaco ad of roughly that era, laying out that egg-on-gas-pedal meme.  The picture above is from that video.

As kids, that was pretty much beaten into us.  Responsible driving means no jackrabbit starts, no tire-smoking stops.  Easy does it.  We’re in the middle of a prolonged gasoline shortage, after all.

So now I come to the part that is absolute heresy for someone of my generation.  If you’ve absorbed the prior two sections, you realize that this advice probably isn’t correct for an EV.  Why?  To consume power at a constant rate over the course of an acceleration, you should start off with a brisk rate of acceleration, then diminish that as the car speeds up.

In other words, if you drive an EV, drive with a lead foot.  Not all the time.  But at the start of every acceleration.  And the end of every deceleration.

If you drive an EV, chuck the egg.


The Prius Prime Eco display

Source:  Underlying picture is from Priuschat.

With that understanding in hand, I’m finally starting to make some sense of the “eco” display on my wife’s Prius Prime.

In theory, this little gauge is giving you guidance on how to drive the car most efficiently.  In practice, I could never make head or tail out of it, except that it seemed to be telling me to drive with a lead foot.

Which, I now understand, it was.

On this display, if you put your foot on the gas, it will show you your actual throttle (gas pedal) position, and the gas pedal position that will, in theory, give you greatest efficiency.

By contrast, when you put your foot on the brake, it doesn’t show you the brake pedal position.  Near as I can tell, it shows you the amount of power than you are generating.  That is, a constant brake pedal position will lead to a shrinking bar, as the car slows down and less energy is generated.

Watch what happens if I try to accelerate gently:

It’s possible that all the meter is actually telling me is that a very lightly-loaded electric motor will operate inefficiently.  I don’t think the Prius eco monitor is actually trying to get me to drive at constant power.

Edit 3/11/2024:  After driving around with a ScanGauge III, my conclusion is that accelerating at constant power is exactly what the eco-meter is trying to get you to do.  It wants you to start off with a heavy foot, and then, as you accelerate, it wants you to back off.  Near as I can tell, that bar is set up to keep you at around 23 HP of power output, or 50 amps of discharge current, or a “2 C” rate of discharge, for this battery.

In particular, my diagram above is labeled wrong. The two red arrows should be labeled “desired power output” and “actual power output”.  You will notice that if you don’t move the gas pedal, the “actual power output” line will creep up as you speed up.  The only way to keep that line in the same place is to back off the gas as your speed increases.  So that line isn’t the throttle position, it’s the power output (power = force x speed).

But no matter how I arrive at it — from theory, or from finally paying full attention to the Prius eco meter — the whole drive-like-there’s-an-egg-between-foot-and-gas-pedal is clearly obsolete.  Gentle acceleration may get you your best mileage in a gas-powered vehicle.  But it’s not the correct way to drive an EV.

Post #1617: When will the tear-down boom end, the sequel.

 

It hasn’t been possible to buy a small house in Vienna, VA for at least a decade now.   Every small house that goes up for sale is purchased by developers, who then proceed to tear it down and build the largest house that will fit onto that lot.

This sustained destruction of middle-class housing, replacing it with lot-filling McMansions, is what I have termed “the tear-down boom”.

I have written about the various implications of the tear-down boom.  Among other things, this continual replacement of small houses with gigantic houses means that:

  • Post #519.  Town revenues from residential real estate have been pushed materially higher by the resulting increase in the price of the houses.
  • Post #308.  There’s a tremendous mis-match between the stock of houses in the Town of Vienna, and the houses available for sale.  Middle-class people can live here — if they already own a house — but they can’t move here, because all the middle-class houses are replaced with McMansions before being re-sold.  As a result, increasingly, Vienna is a town for the wealthy, not the middle class, something I termed the “Mcleanification” of Vienna.

And yet, some of the economics of the tear-down boom just didn’t seem to make a lot of sense, simply as way to generate housing stock.  People really don’t need 10,000 square foot houses, and everything I read about the next Gen X and later is that they have no interest in buying such gigantic pieces of real estate.  Seemed like a classic case of “sell it to whom?”.

The best explanation I could give for the tear-down boom is that it was the result of two toxic Federal economic policies.  These were the huge tax advantages to home ownership, including both tax sheltering of current income and tax-exemption of any capital gains, and near-zero real (inflation-adjusted) interest rates.   In 1997, the Federal government eliminated capital gains on housing.  (With some limits.)  That was on top of the tax sheltering that housing provides via income-tax deductibility of mortgage interest and property taxes.  Then, in 2008, the Fed dropped inflation-adjusted interest rates to zero or below, following the near-collapse of the U.S. financial system.

Between those two policies — the tax advantages and the free money — it became ludicrously cheap to finance the purchase of a mega-home.  And that mega-home was a highly-leveraged investment that was, ultimately, better than tax-free.

But trees don’t grow to the sky.  Back in 2019, I asked “When will the tear-down boom end?”  That was Post #217.

Even then, the market was showing some oddities.  Oddity #1 is that these mega-homes were appreciating less rapidly than adjacent lower-priced homes.  Oddity #2 is that the changes in tax law in 2018 made it much more expensive to own homes costing over about $850,000.  Here’s the analysis of just how much more expensive it became to carry the cost of a $1.4M house after the 2018 changes in Federal tax law:

Not only did it suddenly cost a lot more to carry that $1.4M house, almost all of the additional cost came from the housing value just in excess of $850,000.  Basically, the law reduced the size of what I would term the “tax efficient” house, that is, the house that earns you the maximum tax breaks as a percent of cost.

As a result, in 2019, I looked at that and said, isn’t this going to put the brakes on the tear-down boom? 

And so far, the answer is no.  Just casually driving around town, these still seems to be a tear-down on pretty much every block.

So far.


Today’s mortgage interest rates.

In this last section, all I want to do is assess the impact of the rise in mortgage interest rates.  Literally, dig up the spreadsheet above, and replace the then-current 4% mortgage interest rate with the current 7% (or so) rate.

Source:  Federal Reserve Bank of St. Louis (FRED) system.

Redoing the analysis, I find that the carrying cost of a $1.4M (small) McMansion in Vienna is now about 50% higher then it was back in 2018.  And 86% higher than it was in 2017, before they changed Federal tax law to reduce the tax advantages of owning an expensive home.

So, to be clear:  Those houses are still big money-makers for the owners, as housing prices have risen steeply in the past year.  That said, if home prices merely stabilize, new McMansions will have after-tax carrying costs in today’s environment that are 86% higher than they were in 2017.

My belief is that this plausibly is going to put a damper on tear-downs in Vienna.

I’ve been wrong about that before.

But I believe it strongly enough that I spent last week painting the front of my house.   That’s a real change for me, because I had simply stopped doing any maintenance on my house that didn’t directly affect occupant health and safety.  I figured, why bother to keep the place up, when they’re just going to tear it down when I eventually move?

I was letting the house deteriorate, peeling paint and all.  But now I have about a decade’s worth of deferred basic maintenance to do. Because in today’s environment, it’s no longer a given, I think, that this house will be torn down when I leave it.

Post #1614, COVID-19, new case plateau

 

We’ve definitely hit a plateau in daily new cases.   We’ve been at 12 / 100K / day for well over two weeks now, and it’s reached the point where that flat spot is easily visible on the graph of new cases.

Still, there’s no uptick in Canada, no clear north/south differential in the U.S., and Europe seems to be getting over its “winter wave”, such as it was.

So this level of virus in circulation in the U.S. may just be the new normal.

Graphs follow.

Continue reading Post #1614, COVID-19, new case plateau