Cities Turning to Bicycles



Tim McNamara wrote:

> [email protected] (Brent P) writes:
>
>
>>In article <[email protected]>, Tim McNamara wrote:
>>
>>
>>>Indeed, my review of some of the traffic management literature
>>>(e.g.,
>>>http://ops.fhwa.dot.gov/Travel/traffic/freeway_management_handbook/chapter5.htm)
>>>suggests that traffic flow obeys the mathematics governing
>>>hydraulic flow, and that there is a maximum throughput in any
>>>hydraulic system before turbulence is created. Turbulence in turn
>>>creates drag and slows throughput dramatically. You can set the
>>>speed limit at the 85th percentile, but that will not "smooth out"
>>>traffic flow when there are just too many cars on the road at the
>>>same time- which is about 8 hours of every day in major urban
>>>areas.

>>
>>A smooth flow can sustain a higher throughput delaying the onset of
>>traffic jams and lessening how long they last.

>
>
> In an ideal world, sure. But you're dealing with a situation where by
> definition 85% of drivers are driving below the posted limit- which
> means the faster drivers are tailgating, trying to pass, and creating
> turbulence in the traffic flow. This rapidly becomes congestion.
> You're also dealing with drivers of radically different driving skills
> and driving preferences, so you get people driving 45 mph in the
> center lane on a road posted at 80 mph (in your ideal scenario of
> using the 85th percentile).


Whoa! Hod it right there! That person should get a ticket - no matter
what the speed limit is. That's a completely separate issue, and
another pet peeve of mine. Slow traffic stays to the right, faster
traffic passes to the left, that way nobody gets "held up" until the
highway is completely full. that's the way it's *supposed* to work,
anyway. The idea is to make it more like a laminar flow than a
completely turbulent one.

nate

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Brent P wrote:

>
> I would suggest Frank ride his bicycle through a decreasing radius turn
> that wasn't visable until he was in it such that it forced him to brake
> hard. This would probably be the best lesson as to why this sort of
> design should be avoided. Braking while turning is as ill-advised on a
> bicycle as it is driving. Probably more so.


:)

Almost every time I make a turn on the bike, it's done with a decreasing
radius, and with braking while in the turn! This is normal for a bicycle!


Sheesh. Newbies!


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--------------------+
Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]
 
"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> The computer modeling for this makes it very clear and closely mimics
> life. A traffic jam during rush hour can literally be caused by one
> car hitting the brakes, with other drivers reacting and creating a
> chain of events that lead to slow or stopped traffic. The "stopped"
> part of the traffic sort of cascades backwards from the original site,
> with the driver who caused it normally being blithely unaware of the
> havoc he wreaked when he dropped his cell phone. If somebody going 80
> mph and needing significantly more stopping distance than someone
> going 55 mph rear-ends this joker, you've got a much worse traffic jam
> on your hands.


I was in one of these one time and nearly got creamed from behind.
My Corvette had plenty of stopping power, but the cars behind me
couldn't stop that quick. Luckily, one car was able to go around and
stop on the left shoulder and the other car went around and stopped
to my right. I was even letting up on the brakes to get as close as
possible to the car in front of me because I could see what was
happening behind me.

Someone up ahead less than an 1/8 of a mile had come to a
complete stop for no apparent reason. We were all lucky that there
were no collisions because we were driving at about 60 mph
when this happened. I could see ahead and there was nothing in
the road and I didn't see anything when we started moving again.

This type of thing is why speeding and tailgating can be so
dangerous. People can do things for no apparent reason and
you need some room to react.
 
Frank Krygowski wrote:

> Mark Jones wrote:
>
>>
>> I really find it hard to understand how he could justify a decreasing
>> radius turn as being a reasonable thing to build. Just because a
>> roading program can spit out the stakeout points for a particular
>> piece of roadway, that doesn't mean that it is a good idea to build it.

>
>
> I can tell you're finding it hard to understand! Look, let's think
> about this:
>
> Say you're laying out a two-lane road. Are you prepared to say every
> curve MUST be a constant radius - that is, a circular arc? Of course
> not. That's impractical, given difficulties with contours, rivers,
> right-of-way access, etc.
>


Any curve where the next straightaway is not visible from the entrance
to the curve, i.e. "blind" curve, yes.

> If there is ANY deviation from a perfectly circular arc, there MUST be
> either a decreasing radius or an increasing radius. And if the radius
> increases for drivers heading west, it MUST decrease for drivers heading
> east on the two-lane road.


And when this occurs, it *must* be visible to a driver entering the curve.

>
> Obviously, this happens all the time. It's normal. And drivers handle
> it in a normal fashion. If a driver has an inability to negotiate such
> a curve, he's simply not competent.


ASSuming that the curve is completely visible from its entrance, yes,
this is a correct statement.

>
> If a driver can handle it on a two lane, but not on a freeway, it can
> only be because he has unrealistic expectations. I know of no design
> manual that forbids these things.
>
> If anyone _does_ know of such a manual, let's have a quote or two.
>


I suspect that this is probably hidden in the AASHTO Green Book, but it
is not on the web; if you want to read it you'll have to purchase a copy
from them.

nate


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In article <[email protected]>, Tim McNamara wrote:
> [email protected] (Brent P) writes:


>> A smooth flow can sustain a higher throughput delaying the onset of
>> traffic jams and lessening how long they last.

>
> In an ideal world, sure. But you're dealing with a situation where by
> definition 85% of drivers are driving below the posted limit- which
> means the faster drivers are tailgating, trying to pass, and creating
> turbulence in the traffic flow. This rapidly becomes congestion.


Less rapidly with 85th% limits and KRETP, than the current LLBing
situation with under posted limits.

> Seems to me you are only looking at the up side which fulfills your
> desire to drive faster than you legally can now.


85th percentile limits won't allow me to drive any faster than I do now.
Legally isn't even a consideration because enforcement of the underposted
limits is effectively zero for the speeds I drive.

I am selfish in that I want better flow. I grow tired backups caused by
one LLB who refuses to yield the passing lane to the 15 people behind
him.

> There are serious
> problems to raising speed limits and with the 85th percentile
> proposal.


A loss of revenue being the only one.
 
In article <[email protected]>, Frank Krygowski wrote:
> Mark Jones wrote:
>
>> "Frank Krygowski" <[email protected]> wrote in message
>> news:[email protected]...
>>
>>>I'm not interested in excuses about how difficult decreasing radii can be..

>>
>>
>> This is bad design. For a PE to say what you just said is ridiculous.
>> To resort to a decreasing radius means that the overall design is flawed.
>>
>> You should be able to go through a curve without needing to slow
>> down the whole time. This is how you end up with trucks on their
>> side with their cargo spilled all over the place.

>
> Are you saying you couldn't handle a decreasing radius curve? Do _you_,
> personally, need to have only _increasing_ radius curves to be able to
> successfully stay on the road?


Right for the insulting comments. Typical Frank.
 
Mark Jones wrote:

>
> I really find it hard to understand how he could justify a decreasing
> radius turn as being a reasonable thing to build. Just because a
> roading program can spit out the stakeout points for a particular
> piece of roadway, that doesn't mean that it is a good idea to build it.


I can tell you're finding it hard to understand! Look, let's think
about this:

Say you're laying out a two-lane road. Are you prepared to say every
curve MUST be a constant radius - that is, a circular arc? Of course
not. That's impractical, given difficulties with contours, rivers,
right-of-way access, etc.

If there is ANY deviation from a perfectly circular arc, there MUST be
either a decreasing radius or an increasing radius. And if the radius
increases for drivers heading west, it MUST decrease for drivers heading
east on the two-lane road.

Obviously, this happens all the time. It's normal. And drivers handle
it in a normal fashion. If a driver has an inability to negotiate such
a curve, he's simply not competent.

If a driver can handle it on a two lane, but not on a freeway, it can
only be because he has unrealistic expectations. I know of no design
manual that forbids these things.

If anyone _does_ know of such a manual, let's have a quote or two.


--
--------------------+
Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]
 
"Frank Krygowski" <[email protected]> wrote in message
news:[email protected]...
> Again: people who defend night driving at 75+ mph on rural two-lane
> roads lack the judgement to comment on mitigating neighborhood speeding.

I can't think of any two lane roads near where I live that I would
consider doing 75+ mph at night. Too risky when you consider
that it isn't just other motorists that you need to be concerned
with. Wild animals tend to roam about at night and may wander
out onto the roadway. Hitting a deer would ruin your night.
 
fbloogyudsr wrote:


> Yes, he's a prof at Youngstown, has a BS & MS in Engineering (looks like
> the general engineering type of degree), along with a PE license (in
> Penn, not OH).


Nope. Ohio too.


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Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]
 
Nate Nagel wrote:

[I-79 curve]
> To return to the original point of this whole example - it is clear that
> there are times and places where greatly reduced speeds may be necessary
> for safety reasons.


IIRC, that particular curve is accompanied by a series of reduced speed
ahead and reduced speed limits rather than advisory speeds. I believe
that within a mile it drops from 65 to 55, then 45, then 35, and finally
25 mph. If there were only advisory signs, there would be a lot more
crashes because a decreasing radius curve that can be negotiated at 35
mph max is the last thing one expects on an interstate (and exemplifies
the inherent problem with chronic misuse of advisory signs on most roads).
 
In article <[email protected]>, Tim McNamara wrote:

> But will it narrow the distribution of speeds? Will the people who
> drive no faster than 50 or 55 mph now suddenly decide they'll happily
> drive at 75 or 80 just because the speed limit got raised?


If you are driving 50 or 55mph on a chicago interstate it's because you
can't get another ticket, you believe in slavish obedence to the law,you
are carrying drugs, you are carrying explosives, your vehicle shouldn't
be on the road at all, you are in no condition to be driving, or you are
doing some sort of traffic experiment.

Because I see even old women drive their age on local interstates. And they
aren't younger than 70.
 
"Frank Krygowski" <[email protected]> wrote in message
news:[email protected]...
> Are you saying you couldn't handle a decreasing radius curve? Do _you_,
> personally, need to have only _increasing_ radius curves to be able to
> successfully stay on the road?
>
> How about on a two lane road? Do you want to see only increasing curve
> radii when you're heading, say, east?
>
> And Mark - what sort of engineering tricks do you want used when you
> turn around and drive west?


They are called constant radius curves. Much safer than decreasing
radius curves.
 
In article <[email protected]>, Frank Krygowski wrote:
> Brent P wrote:
>
>>
>> I would suggest Frank ride his bicycle through a decreasing radius turn
>> that wasn't visable until he was in it such that it forced him to brake
>> hard. This would probably be the best lesson as to why this sort of
>> design should be avoided. Braking while turning is as ill-advised on a
>> bicycle as it is driving. Probably more so.

>
>:)
>
> Almost every time I make a turn on the bike, it's done with a decreasing
> radius, and with braking while in the turn! This is normal for a bicycle!


> Sheesh. Newbies!


Not braking by coasting frank. braking with the brakes. Coasting is
normal on the road, not squeezing the hand brakes.
 
Nate Nagel wrote:

>
> Blind curves should *never* be decreasing radius. Never. If a road has
> traffic in two directions, a blind curve should be, by necessity,
> constant radius.


:) I thought you had driven in West Virginia. And Western Pennsylvania.

So every road that has to curve around an Appalachian hill should have
the hillside sculpted into a perfect circular arc?



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--------------------+
Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]
 
"Frank Krygowski" <[email protected]> wrote in message
news:[email protected]...
> How about on a two lane road? Do you want to see only increasing curve
> radii when you're heading, say, east?


Might have to ask my brother what kind of problems he has seen
with these. He is a policeman and has had to work a lot of vehicle
accident scenes.
 
Nate Nagel wrote:

> Frank Krygowski wrote:
>
>>
>> Perhaps you should start with how you see miles in the dark in Nevada.
>> Then tell how it works in Virginia.
>>

>
> It's really easy, you just flip on the high beams.


It's fantasy time! ;-)


>
> A nice bonus of the flat terrain is that the moonlight actually helps
> you, as the only shadows are from the trees.


So, how many miles would you say you can normally see? I'm curious
about your estimate. (Those are some headlights!)

--
--------------------+
Frank Krygowski [To reply, remove rodent and vegetable dot com,
replace with cc.ysu dot edu]
 
"Frank Krygowski" <[email protected]> wrote
> fbloogyudsr wrote:
>> Yes, he's a prof at Youngstown, has a BS & MS in Engineering (looks like
>> the general engineering type of degree), along with a PE license (in
>> Penn, not OH).

>
> Nope. Ohio too.


Then update your "home page" on the Y. U. site.

Floyd
 
Frank Krygowski wrote:

> Nate Nagel wrote:
>
>>
>> Blind curves should *never* be decreasing radius. Never. If a road
>> has traffic in two directions, a blind curve should be, by necessity,
>> constant radius.

>
>
> :) I thought you had driven in West Virginia. And Western Pennsylvania.
>
> So every road that has to curve around an Appalachian hill should have
> the hillside sculpted into a perfect circular arc?
>


There's a huge difference between a western PA goat track and an
Interstate highway. A road cut into a hillside you expect to be
surprised, and allow a little extra cushion in your speed. Especially
when said Interstate highway has a curve in it that looks for all the
world like a standard cloverleaf kind of thing until you're already
committed to it.

I'll post this again, since you clearly didn't look at it the first time:

http://www.gribblenation.com/hfotw/exit_50.html

Notice how there appears to be maybe a 55 MPH typical cloverleaf as you
enter the turn, but once you get maybe 20 degrees in you suddenly
discover that it's actually a sharp hairpin and what you thought was the
actual curve was really nothing much at all. Again, poor highway design.

But the point is, **** happens. Sometimes highways get built with less
than optimal design features, and we have to deal with them. This one
is particularly bad, as it's deceptive. So there are warning signs to
alert drivers to the special hazards of the situation. The question
that has remained unanswered throughout this long, tedious thread is,
"how do you communicate to motorists the concept of 'yes, I know every
exit ramp on the East Coast is signed at 25 MPH which is generally 20
MPH pessimistic, but even though this sign looks exactly like all those
other signs and you aren't even exiting the freeway, we really, really
mean it this time, so slow down.'"

To extend it to the discussion of your neighborhood, the analogy is "I
realize that you do most of your driving on the freeway, where the speed
limit signs are generally 20 MPH or more pessimistic, but even though
this 25 MPH sign looks just like those freeway speed limit signs, we
really, really mean 25 MPH, so slow down."

Heck, perhaps you should just have *that* printed on a sign, to go on
the same post as the speed limit sign. At the very least, I'd get a
chuckle out of any municipality that had the balls to post something so
honest.

nate

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"Frank Krygowski" <[email protected]> wrote in message
news:[email protected]...
> Nate Nagel wrote:
>
> >
> > Blind curves should *never* be decreasing radius. Never. If a road has
> > traffic in two directions, a blind curve should be, by necessity,
> > constant radius.

>
> :) I thought you had driven in West Virginia. And Western Pennsylvania.
>
> So every road that has to curve around an Appalachian hill should have
> the hillside sculpted into a perfect circular arc?

This has devolved from the original discussion concerning freeway
exit ramps. That is where I do not consider decreasing radius
to be a good idea.

In the mountains, you just have to slow down and understand that
the curves can have varying radii and can even switch directions
part way through them.

These are two very different design situations and drivers in the
mountains should expect the road to be very complex. You get
all kinds of compound curves and elevation changes going
both up and down over relatively short distances. If you drive
fast in a unfamiliar place in the mountains, it may be the last
thing you ever do.
 
Arif Khokar wrote:

> Nate Nagel wrote:
>
> [I-79 curve]
>
>> To return to the original point of this whole example - it is clear
>> that there are times and places where greatly reduced speeds may be
>> necessary for safety reasons.

>
>
> IIRC, that particular curve is accompanied by a series of reduced speed
> ahead and reduced speed limits rather than advisory speeds. I believe
> that within a mile it drops from 65 to 55, then 45, then 35, and finally
> 25 mph. If there were only advisory signs, there would be a lot more
> crashes because a decreasing radius curve that can be negotiated at 35
> mph max is the last thing one expects on an interstate (and exemplifies
> the inherent problem with chronic misuse of advisory signs on most roads).


You may be right, it's been a couple years since I've been up that way,
and I was unable to find a good picture on the web of the actual
signage. However, you just described to a tee the signage on I-70 as
you approach US-30 in Breezewood, which is a complete non-event - yeah,
there's a tee intersection with a traffic light, but you can see it from
a mile away. Same thing with the rumble strips and reduced speed signs
two miles before a toll plaza. Obviously PA highway engineers never
heard of Chicken Little.

Speaking of which, whose brilliant idea was it to plunk down a toll
plaza right in the middle of the PA Turnpike? Freaked me right out the
first time I saw it. One thing the 'pike had going for it over other
toll roads was that you paid when you entered the state or got onto the
'pike, and then didn't have to stop again until you got off or left the
state on the other side.

nate

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