Post #1120: Sidewalk cost per foot, and the Robinson sidewalk bequest.

This post is a little calculation regarding the fraction of the Robinson sidewalk bequest that the Town of Vienna will be able to spend.  Best guess, it looks like the Town might be able to spend about 6% of that bequest money.  Plausibly, the Town will spend less than the interest that fund earns during the five years that have been allotted for the Town to spend it.


Timeline

As you probably know if you’re reading this, former Town Council member Maud Robinson left a large bequest to the Town of Vienna, for the purpose of building sidewalks.

Maud Robinson passed away in March of 2019, at the age of 96.  She made a bequest to the Town of Vienna, leaving (then) roughly $7M to be used for building sidewalks.  (That has since reportedly grown to $9M).  The Town of Vienna appears to have been notified of her bequest in documents dated April 2019.   There’s a time limit of five years, for getting that money spent.

And so, if I have that all correct, the Town has until April 2024 to get those sidewalks completed.

Nothing much appears to have happened during the first year following the bequest.  The first I heard this publicly discussed by Town Council was about a year later, when plans were announced to put sidewalks along three streets (Post #532, February 25, 2020).

A year after that, I went to check on one of those streets, but no construction had begun (Post #1056, March 14, 2021).   I was surprised at the time, but then realized that the Town typically takes two years to get a sidewalk built. 

That two-years-to-build-a-sidewalk estimate is important, because as I understand it, a) the Robinson trust only disburses funds once the sidewalk is actually built, and b) the funds have to be dispersed prior to mid-April 2024.  If it takes two years to get one built, that means the Town has until roughly April 2022 to get those sidewalks started.  Possibly, they could start some later, and hurry the construction a bit.  But so far, there’s not a lot of evidence that they are hurrying.

And now, in April 2021, the Town appears to have a final plan for most of what they proposed to do, to use the Robinson Estate sidewalk bequest.  This will be formally revealed at this Monday’s Town Council virtual meeting.  The documents outlining that plan are available at this Town of Vienna Granicus web page.


A brief calculation

I went looking for one specific figure in the documents outlining the Town’s plan:  What fraction of the money from the Robinson bequest is the Town actually going to be able to spend? 

I came up empty handed.  There’s nothing anywhere near so straightforward in those documents.  Near as I can tell, there isn’t even an estimate of total miles of sidewalk to be built.  There’s an exhibit labeled “Projects — status at a glance, with costs”.  Unfortunately, there are no costs listed in that document.  It’s just a list of recommended projects.

The Town’s great handicap here is that the executor for the Robinson trust insists that the money be spent literally only on the sidewalk, and nothing associated with the sidewalk (e.g., not for the curb and gutter next to the sidewalk).  So, literally just the flat thing you walk on, which is, in fact, the least expensive part of actually constructing sidewalks.

To be clear, there is no such explicit restriction in the bequest itself.  E.g., the words “curb” or “gutter” do not appear in that document, based on reporting from credible sources and an image of the key clauses of that document that was posted on Facebook.  That restriction is the interpretation of the executor, which the Town chose not to challenge legally. 

If you are capable of doing long division, it’s immediately evident that this restriction is completely at odds with the size of the bequest.  In a nutshell, it makes is so that no material portion of the bequest could actually be spent.  Effectively, it makes the bequest logically inconsistent. This was obvious a year ago, see Post #532, February 2020.

“Problem 2:  The Commonwealth of Virginia says that standard 5′ ribbon sidewalk costs about $30 per linear foot.  (See reference in Post #521).  The Robinson Estate has granted the Town up to $7M to spend on sidewalks.  How many linear miles of sidewalk must the Town choose in order to use up the full $7M gift?

Hint 1:  7,000,000 ÷ 30 = 233,333.  Hint 2:  233,333 ÷ 5,280 = 44+

Reference number:  In total, Vienna has about 65 miles of publicly-maintained roadways (reference).”

In any case, per the 44 miles answer in the word problem above, it was obvious a year ago that, with this restriction, the Town was only going to be able to spend a tiny fraction of the available money.   Particularly if the Town would not spend its own money to build curb and gutter.

(By contrast, the full cost of constructing a sidewalk, including everything you need for that sidewalk, can be orders of magnitude higher than the cost of the five-foot-wide concrete ribbon that you walk on.  I did a post more than a year ago that looked at the variation in cost per foot across four projects actually undertaken in the Town of Vienna (Post #521), which ran from $100 to $666 dollars per linear foot.)

Weirdly, with all this perseveration on streets that have curb and gutter, the curb and gutter itself doesn’t cost much.  Per reasonably recent set of estimates via VDOT (.pdf), (same reference as that cited immediately below), if the sidewalk itself costs about $30 per foot, the curb and gutter costs a further $40.  Really, for expensive sidewalk projects, neither the sidewalk nor the curb-and-gutter is the expensive part of the project.

And so, the question isn’t whether or not the Town is going to be able to take full advantage of those funds.  Without challenging that restriction legally, it clearly won’t.  The only question to be answered, now that there is a plan, is just how small a fraction of the current $9M bequest is the Town actually going to be able to use, given the path it has chosen to take.  And that’s what I’m going to calculate next.

The Commonwealth of Virginia, and by reference, Fairfax County estimates that it costs about $30 per linear foot to install sidewalk in this area.  That’s just the sidewalk, not the curb, gutter, or other items incident to the sidewalk.  That’s based on Virginia Department of Transportation project-planning standards, and you can find that approximate figure in in this VDOT report regarding a couple of transit corridors in Fairfax County.

And so, if the trust will only pay for literally the sidewalk, and sidewalk costs about $30 a foot, if the Town would list the total footage, I could figure out the likely total spending from the trust.  And compare that to the $9M that was potentially available.

The Town doesn’t list the footage in the current document.  That means either a) I take the maps provided, attempt to interpret the map key, and tediously measure the road lengths, b) I extrapolate based on the number of projects, from the first three projects where I did measure road lengths, or c) I just take somebody’s word for how much sidewalk the Town is planning to build.

Here, I’m going with c), as Councilman Potter has been quoted that the Robinson trust money will allow 3.3 miles of new sidewalks.  (That’s per this source.)  I can’t quite see that, based on the planning documents cited above, but let me just run with that.

  • 3.3 miles x 5,280 feet/mile x $30/foot = $522,270
  • $522,270/$9,000,000 = 5.8%.

So, best guess, at best, the Town will spend about 6% of the Robinson bequest money.  That assumes that a) everything currently being discussed will be built, b) those sidewalks will all be finished before April 2024, c) the trust only pays for the sidewalk, and d) the Fairfax County estimate of $30/foot is a reasonably accurate estimate for the Town of Vienna.

This is about what I would have guessed, a year ago, when I estimated that the first three projects announced would account for about 1% of the then $7M bequest (Post #532)

Just to ballpark it, the Town’s documents list 11 projects that should get the go-ahead this Monday.  By eye, looking at the maps, the longest of those that are up for approval is DeSale St SW, which would be about 3400 feet of sidewalk, assuming new sidewalk on both sides.  (The project for Hillcrest appears longer, but is not yet approved).  If all 11 projects were as extensive as that one, that would work out to be about 7 miles of sidewalk.  Thus, a published estimate of 3.3 miles from Councilman Potter’s statement appears reasonable.

Something about this whole process still strikes me as deeply, fundamentally wrong.  I guess it’s because I’ve been doing the same simple arithmetic for more than a year now, and I still come up with the same question.  If nothing else, this shows you how at odds this restriction is, with the overall size of the bequest.  For the life of me, I can’t believe that the bequest was made in full understanding of how little of it would actually be spent.

In a very real sense, the Town won’t even be able to spend the interest earned on the money, during the time it is held in trust for the Town’s use.

It’s great that the Town has a plan.  It’s good that the least-logical parts of it have been jettisoned (see Post #1096).  I’m sure that most of the people in most of the areas getting sidewalks are happy to have them.  As I have noted in earlier posts, it’s just plain odd that the only way the Town has to target sidewalks to roads that had curb-and-gutter placed decades ago.  And, oddest of all, with this restriction, the Town will be unable to spend a material portion of the money left in trust for this purpose.

Finally, this ends up being one of those cases that economists want to see avoided at all costs.  Mainly, because the money is “free”, and the Town can’t even really start to touch the principal, let alone spend the interest, there’s a real impetus to produce gold-plated sidewalks.  One thing Maud Robinson was clear about was that these sidewalks were to be done under contract.  Presumably, that was to get a fair, market-established price for the work.  It will be interesting to see, if the information is ever released, what cost per foot of sidewalk the Robinson trust ends up paying.

Post #G21-018: Radiant barrier for keeping a raised bed warm at night, final post.

 

I’ve been looking into simple ways to keep to keep a raised garden bed warm at night.  So far, I’ve figured out the following:

  • What doesn’t work:  Floating row cover (Post #G21-012)
  • What does work:  Space blanket plus “passive solar” (Post #G21-014)
  • Why that works:  The math behind the space blanket (Post #G21-015)
  • You need the extra heat input from passive solar:  (Post#G21-017).

I have now learned one two more things. 

First, space blankets are too fragile to be used on a windy day.  That’s unfortunate, because they are cheap and easy to store.  But the windy conditions two days ago showed me that they just aren’t strong enough.  I had to cover the space blankets with a tarp to keep them from being shredded.

Second, actual radiant barrier, made for use in construction, works better than space blankets.  This is material sold for use in home construction.  This isn’t the the bubble-wrap-type Reflectix (r) insulation.  This is more-or-less a piece of aluminum-coated Tyvek (r), and so it’s a heavy, stiff, strong fabric.  I had a roll left over from a prior project and tried it last night, as the weather report called for near-freezing temperatures. Continue reading Post #G21-018: Radiant barrier for keeping a raised bed warm at night, final post.

Post #1119: COVID-19 trends, update to 4/22/2021.

Looks like the U.S. fourth wave is fizzling out.

You may have noticed that the news media are no longer screaming about Michigan.  That’s because things are getting somewhat better there, and that doesn’t make the news.

Source for this and all other graphs of new cases:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 4/23/2021.  https://github.com/nytimes/covid-19-data.  The NY Times U.S. tracking page can be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html.

More than that, the entire Midwest now seems to have topped at just about exactly the same time as Michigan. That’s the sort of synchronous behavior that makes me ask whether there’s still a large element of seasonality to this current wave of COVID-19.  Think about it.  Those states have widely-varying histories (fraction of population already infected), varying rates of vaccination, and varying policies toward (e.g.) re-opening of schools.  And yet, they all appear to peak within a few days of one another?  It’s tough for me to believe that there isn’t some underlying factor causing that behavior.

Be that as it may, more than four weeks into this fourth wave, the U.S. daily new case rate stands just 14% above the low point of the prior wave (marked in red below).  That works out to a growth rate of just 3 percent per week.  That’s not even remotely comparable to the prior three U.S. waves of COVID-19.

I keep using the term “fizzle out” to describe this U.S. fourth wave.  There are no new hotspots to take the place of Michigan.  On the other hand, the virus isn’t going away.  Not anywhere.  Or, at least, not in any state, not even those states that had a large fraction of the population immune via infection.

Here’s a graph of what was, at some time in the past, my top ten candidates for herd immunity, based on having a large share of the population immune via prior infection with COVID-19.   There’s absolutely nothing to suggest that any state is even close to herd immunity.


Tribe immunity

If I contrast what’s just been happening at William and Mary (Post #1117), versus what has happened in Michigan, I’m starting to see some depth to the herd immunity issue.

The W&M student body is largely isolated from the rest  of the world.  As of ten days ago, three-quarters of them had been vaccinated.  And they now appear to have very nearly eradicated COVID-19 within the student body, having had one positive case in the last 4500 or so tests, in the current round of “census” testing of every student on campus.

In Michigan, by contrast, the crisis arose because the virus found itself a fresh, largely uninfected population:  High school students.  The decision to re-open high schools created a pathway for spread of COVID-19 in a population that had largely been protected from it, or, at least, mostly uninfected by it, up to now.

W&M fits the classic model of herd immunity.  That’s a single, isolated, well-mixed population.  With a high vaccination rate, and almost uniformly good COVID-19 hygiene, they have all-but-eliminated the spread of COVID-19 on campus.

But in Michigan, we have numerous sub-groups of the population, and what we have seen of late is that the pandemic has remained alive by rotating to a new targeted group.  Fresh victims, as it were.  There, a large population of unvaccinated individuals  was newly exposed to a situation where transmission was likely.  And so the rapid spread of the virus continued.

Here’s the point:  Michigan wasn’t a flare-up of the virus in the entire population.  It’s not as if they saw a spike across-the-board.  It was mostly due to the spread of the virus to a new target group, high school students, and to a lesser degree, grade-school students and young adults.  My recollection is that for older adults, there wasn’t much of an increase at all in new cases per day.

Michigan had that sub-population of “fresh victims” standing by.  And Michigan saw that flare-up at a time when, according to the standard model of epidemics, infection rates should be tapering off.  Michigan seems to defy the rules, but that’s because the rules don’t really fit the situation in Michigan.

By contrast, within the W&M student body, there is no group of fresh victims for the virus to turn to.  That’s a more-or-less a homogeneous mass of people, living in its own little world.  The refer themselves as the Tribe, and that’s oddly appropriate in this context.  They are a most-vaccinated tribe, and the results are following the standard theory of epidemics.  Tribe immunity, if you will.


Prostatectomies per 100,000 men;  COVID-19 cases per 100,000 non-immune individuals.

In the field of public health, some disease rates are not calculated on a per-person basis.  For example, you won’t see figures for prostatectomies per 100,000 persons.  You will see figures for prostactomies per 100,000 men.  That’s for the obvious reason that women are irrelevant to that calculation, and it makes more sense to calculate incidence of surgery per 100,000 potentially eligible for that surgery.  (You might not think that matters, but if you stratify by age, you’ll find that men account for just 40% of the population age 75+).

A recent Washington Post opinion piece offered a truly profound insight into the current situation with COVID-19.  (Opinion: This is the most dangerous moment to be unvaccinated, by Robert M. Wachter, April 19, 2021).  Or, at least, I found it to be truly profound.  Let me summarize the gist of it, with a little twist.

If you start counting up all the people who are now immune to COVID-19, you realize that the rate of new infections among those who are still capable of being infected is really pretty horrendous.  

The current U.S. new-infection rate doesn’t look too bad, but that’s because we calculate it as new infections divided by the total population. When we do that, we get an average of about 20 new cases / 100,000 population / day.

But when you think about it, that’s like prostatectomies per capita, not per male.  It’s not really an accurate picture of what’s going on.  A large fraction of the population is now immune to  COVID-19, starting with more than half of the adult population having been vaccinated. 

Let me bring my “herd immunity” chart up to date, and then discuss that point.

Source:  Calculated, with a separate assumption as to the ratio of total infections to reported infections, based on the CDC COVID Data Tracker as of 4/22/2021.

By my best-guess estimate, more than two-thirds of the U.S. population should be fully immune to COVID-19 at this point.  And so, when you see the U.S. new-case rate of 20/100K/day,  based on the total population, you should mentally triple that, and say, that’s 60 new cases /100,000 population /day within the population that’s still at risk for infection.

Once you get that in perspective, you see the current situation in a new light.  The U.K. variant is raging within the population still at risk.  The only reason we don’t see that is that two-thirds of the population is no longer at risk.  And when we average those two populations together — 60/100K/day and 0/100K/day — we end up with the seemingly-OK published value of 20/100K/day.

That gets back to the fundamental question for the end of the pandemic:  If two-thirds of us are immune, and we continue to engage in COVID-19 hygiene, why is there still no sign of herd immunity?  That immunity by itself should be able to handle a virus with a basic replication factor (R-nought) of 3.  Toss in the COVID-19 hygiene, and that plausibly should handle the U.K. variant, with an estimated R-nought of maybe 3.5.  Why isn’t that happening yet?

I think the explanation is that the new, more infectious U.K. variant is now finding fresh victims.  It’s jumping to people who would not have been infected, in their normal course of business with the older, less-infectious variant.  As a result, cases are skyrocketing among the portion of the population that remains at risk for infection.

So the U.S. as a whole, with the new U.K. variant being spread, perhaps does not fit the standard model of a pandemic.  It’s not like William and Mary, with a homogenous and well-mixed population.  It’s more like Michigan, with pockets of fresh victims ready to be infected, if only some pathway opens up for the virus to reach them.  And, plausibly, the greater infectiousness of the U.K. variant is the pathway by which the virus continues to spread within the remaining small, non-immune population.

In conclusion:  I haven’t quite figured out what this means for the end of the pandemic.  But, at least, I think this explains why we’re not seeing a swift and clean end of the pandemic, as seems to be occurring at William and Mary.  All across the country, the introduction of the more-infectious U.K. variant means that we’re finding the equivalent of Michigan’s high school students.  We’re finding fresh victims who would not otherwise have become infected.  And we’re now going to have to wait for that process to work itself out before we finally get the total level of immunity in the population both high enough, and homogeneous enough, to suppress further transmission of the virus.

Post #1117: William and Mary, another good day, the math of herd immunity.

Today’s test results were 1-for-1772.  Three days of census testing are highlighted in yellow below.  In short, they’ve tested three-quarters of campus enrollment and found one COVID-19 case.

Again, obviously good news.

This is a follow-up to my last post, and in this I try to explain why you might not want to, or be able to, relax the William and Mary COVID-19 hygiene rules just yet.  Despite this good news. Continue reading Post #1117: William and Mary, another good day, the math of herd immunity.

Post #1116: Town of Vienna, a small lesson from WHOIS, edited.

Edit:  I’ve taken this down, because it offended one of the candidates for Town Council.

My only point is that there has been a lot of ugly stuff said, on social media, about David Patariu.  Not said by other candidates, but said by the peanut gallery.

And a lot of that is just hard to square with the simple observation that he actually helped the incumbents get elected.  And that he wasn’t going to withdraw that little bit of help, now that he’s running against them.  Because that would be dysfunctional, in the greater scheme of things.

There’s a simple point here:  This observation, which I took the time to document, doesn’t fit with the “Dave is a mean asshole” narrative being pushed on social media. 

But my attempt to point that out, without being so crude, managed to backfire, and offended a candidate anyway.

I don’t quite grasp why revealing that Patariu helped the incumbents with their websites, and hasn’t dropped that help despite running against them, was deemed offensive.   But I’ve erased the original post.

I hope this is now completely clear.

Post #1115: William and Mary, zero cases in a further 1599 tests? Sure looks like herd immunity.

Edit:  Oh, no.  My wife tells me this is prompting calls to ease up on the COVID-19 hygiene at William and Mary.    I know it’s tough to grasp, but that arithmetic of epidemics says that would be unwise. 

It’s too late this evening, but I’ll write up the math on that one tomorrow.  Until the virus is no longer in circulation anywhere, the way you keep it from entering and spreading in the W&M student body is via the combination of vaccination and COVID-19 hygiene.  I realize that “herd immunity” is rarely discussed this way, but it’s the combination of those two effects that reduces the transmission rate enough to get you over the herd immunity threshold. 

You risk firing this right back up again if you drop the COVID-19 hygiene portion of this system, given the incidence of new cases in the community.

Original post follows:

Yesterday W&M reported zero new cases in 1488 tests.  Today they reported zero new cases in a further 1599 tests.

Like so:

It’s extremely unlikely that we would observe this, if the recent rate of new infections was continuing.  That’s what yesterday’s math showed. Continue reading Post #1115: William and Mary, zero cases in a further 1599 tests? Sure looks like herd immunity.

Post #1114: COVID-19 update to 4/20/2021.

Not much to say.

Nationally, the rate of daily new cases still appears to befalling, a bit.   Michigan and Minnesota now clearly appear to have peaked.  It doesn’t look like there are any new hotspots arising to take their place.  So it looks like the U.S. fourth wave may have, in fact, peaked.

Whatever the U.K. variant is going to do, it’s pretty much doing it right now.  Per the latest Helix Corporation COVID dashboard data, as of 4/13/2021 more than two-thirds of new U.S. cases were the U.K variant.

The rate of daily vaccinations appears to have slowed, a bit.  In addition, although it is hard to tell from a couple of daily snapshots, the fraction of the elderly who have been vaccinated may finally be topping out.

A few graphs follow. Continue reading Post #1114: COVID-19 update to 4/20/2021.

Post #1113: William and Mary, zero cases in 1400+ tests. Herd immunity?

William and Mary has started another round of “census” testing, administering COVID-19 tests to all students on the campus.  Yesterday, an email from the W&M administration said that test results should start appearing on the W&M COVID-19 dashboard.  And they have.

Yesterday, W&M reported test results for 1448 students.  They found no (zero) positives.  Zero new COVID-19 cases, out of 1448 tested. Continue reading Post #1113: William and Mary, zero cases in 1400+ tests. Herd immunity?

Post #G21-017: Warming a raised bed at night 3: passive solar helps.

This is a continuation of a series of posts on how to keep the surface of raised beds warm during cool spring nights.  So far I have shown:

  • What doesn’t work:  Floating row cover (Post #G21-012)
  • What does work:  Space blanket plus “passive solar” (Post #G21-014)
  • Why that works:  The math behind the space blanket (Post #G21-015)

Here, I answer two more questions.  Yes, you need the passive solar input (jugs of water than have warmed in the sun).  Or, at least, that clearly helps quite a bit.  And no, you won’t kill your plants if you forget to remove the space blanket the next day. Continue reading Post #G21-017: Warming a raised bed at night 3: passive solar helps.