🚀 go-pugleaf

Bentley <bentley@access4.digex.net> wrote:


>Heh. Back at you -- define "medium sized" and "significant!"

A medium sized city (I also said small ones) has under a half million
people in it. "Significant" congestion would, IMO, mean more than an
hour of "rush hour" traffic backups, which would equate to Level of
Service F.

>I know there are specific efficiency levels that transportation engineers
>strive for; there was an excellent article in the Washington Post several
>years ago that described the methodology in non-technical terms.

They are called "levels of service", and range from A (the best) to F
(the worst).

>Unfortunately I have lost it. Anyhoo, I seem to remember that 40mph
>offered the best mix.

Around that speed, the combination of speed and volume of traffic
reach what is called capacity of a controlled access highway. The
curve of speed and capacity is a half parabola on its side with the
open end facing toward the left. As capacity increases (the horizontal
side of the graph), speed begins to gradually decrease (the vertical
side of the graph). At some point the curve steepens, and you get no
further increase in capacity for a comparable reduction in speed.

At that point you've got Level of Service E, which is the maximum
capacity of the road. Speeds tend to reach about 30-40mph at that
point. 

>So. "My" definition of congestion is when highway traffic drops below
>30mph. The clock starts then. A "city" to means a town with a population
>greater than 100,000. 

My numbers are a bit higher in both categories. See above.

>"Significant." Aye, there's the rub. I submit that any of my "cities"
>experiences at least an hour of my "congestion" each year, if simlpy
>because sporting events and weather and accidents cause traffic tie ups. I
>can't prove it. But if Des Moines has a tractor trailer flip on day in
>Decemeber, and it closes the road for an hour, that's really not what
>we're talking about, is it? No, I think the important distinction is
>consistency.

This is correct. Any road can experience backups if there's an
accident on them, regardless of the amount of traffic on it.

> The eastbound approach of the Woodrow Wilson Bridge is backed
>up every day; sometimes it starts at 4:00pm, on Fridays it can start as
>early as 2:30pm. And it's not because of bridge openings or truck
>accidents, it's because it's a bottleneck.

I wasn't disagreeing with your claim that Washington DC has
congestion. Obviously it does. I just disagreed with your claim that
EVERY city has congestion.

> Now, to answer your question, I
>have to say if there are similar bottlenecks in every "city." I don't
>know. I suspect there are. So we have to hash this out a little to come to
>terms. What are the six you're thinking of?

Chattanooga, Wilmington, NC, Asheville, NC, Charleston, SC. I confess
I cannot think of two others that I personally can say don't have a
lot of congestion. I'm sure there are several others around the
country, though.

I'd throw Raleigh-Durham into the mix if I kept out I-40 and US 64,
but that wouldn't be fair...

> I'll throw one out, that I
>have a little experience with: Topeka. I never recall seeing stopped or
>even slow traffic during my half-dozen business trips there.

Then your claim that "all cities have congestion" is thereby
incorrect, without any examples of my own.

John Lansford, PE


The unofficial I-26 Construction Webpage:
http://users.vnet.net/lansford/a10/