Cities Turning to Bicycles

"Frank Krygowski" wrote in message
...
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.
We have wandered away from what we were originally talking about
and I wasn't clear enough in what I wrote. The only place where
I feel that varying radius curves shouldn't be used is on the exit ramps
where a clover leaf design is used. I have seen overturned trucks
on these and learned for myself one time just how dangerous
they can be if you enter the ramp even a little too fast.

I could picture what I thought we were talking about, but I wasn't
aware that the scope of this had broadened to cover the open
highway.

In the hills, varying radius curves are used all the time. I have driven
in the mountains, and you need to pay attention to the posted limits
if you value your life. This is particularly true if you are unfamiliar
with the area.

Alan Baker wrote:

I've driven my brother's Nissan Pathfinder (even before it had its
shocks replaced) and it can easily -- easily -- more than double the
advisory speeds on most ramps.

Advisory speeds are based on the comfort level of a driver driving a
1939 Ford Vehicle. The lateral force would be enough to have a "ball on
a string" deviate 10 degrees from the vertical position. Most drivers
take curves such that the deviation would be between 12 and 14 degrees,
IIRC.

Mark Jones wrote:
"Frank Krygowski" wrote in message
...

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.


IOW, you seriously think all curves must be constant radius. Astonishing!

I might expect this idea to come from a novice driver just learning to
steer - and unaware of the complexities of real life engineering. But
for a licensed driver to say this is amazing.

I suggest you get a 1:24000 USGS map of any hilly area you plan to drive
through. Examine it in detail before you leave. You'll find _many_
curves you'll want to avoid.

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

Brent P wrote:

In article , 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.

Yes, braking with the brakes, Brent. While in a curve. Every day.
It's quite normal.


--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
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Nate Nagel wrote:

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.

Seems to me you should _always_ allow a reasonable cushion in your
speed. If you ever find yourself driving at ten tenths on a public
road, you've made a mistake.

Now, mistakes happen. But it's a bit immature to admit your mistake,
describe it in great detail, then try to pass it off as impossible to
avoid. And that's pretty ineffective, too, when others can point out
that they did _not_ make that mistake.

And if you meant the mistake was merely difficult (not impossible) to
avoid - then those who have avoided it have demonstrated greater
competence than you did, haven't they?

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
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Mark Jones wrote:


This has devolved from the original discussion concerning freeway
exit ramps.

It's now far removed from the issue which concerns me - which is
controlling irresponsible drivers in non-freeway situations. I should
bow out.


--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
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edu]

In article , Frank Krygowski wrote:
Brent P wrote:

In article , 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.

Yes, braking with the brakes, Brent. While in a curve. Every day.
It's quite normal.

Not surprising given your other foolishness. It also shows that you
likely putter along at sidewalk speeds. At the road speeds I ride
braking in a turn on a bicycle begins to overtax the avialable traction.

A bicycle like any other vehicle has a finite amount of traction. It can
be used for braking, accelerating, or turning and any combination there
of. This is why it is proper form to brake before entering the turn. I
brake to the speed I can take the turn at, remain at that speed or coast
into the turn and accelerate out.

Arif Khokar wrote in message ...
Alan Baker wrote:

I've driven my brother's Nissan Pathfinder (even before it had its
shocks replaced) and it can easily -- easily -- more than double the
advisory speeds on most ramps.

Advisory speeds are based on the comfort level of a driver driving a
1939 Ford Vehicle. The lateral force would be enough to have a "ball on
a string" deviate 10 degrees from the vertical position. Most drivers
take curves such that the deviation would be between 12 and 14 degrees,
IIRC.

found this site:

http://manuals.dot.state.tx.us/dynaw...ult;ts=default

I don't see any mention of a 1939 Ford, but essentially that appears
to be correct. They do apparently allow higher G-forces for very slow
speed turns, but 10 degrees is the recommended value for 35 MPH or
higher. In any case the maximum value allowed is 14 degrees, still
far less than people seem to find acceptable in day to day driving. I
wouldn't be surprised if a 10 degree ball bank indicator reading *was*
perfectly safe and comfortable in a bone stock '39 Ford, honestly.
Perhaps it's time to revisit these standards; how often is a vehicle
in regular use anywhere in the US older than the mid-late 1960's?

Key quote: "The speed to be posted on the curve should not be reduced
arbitrarily below that determined by the procedures provided in this
section." Hmm, looks like *that* recommendation isn't followed across
the board...

Note that there really isn't *any* hard standard for advisory speeds
for exit ramps, although obviously I have no way of knowing if that
section of this document is derived from the Green Book or is unique
to the state of TX.

nate

Brent P wrote:

In article , Frank Krygowski wrote:

Yes, braking with the brakes, Brent. While in a curve. Every day.
It's quite normal.


Not surprising given your other foolishness. It also shows that you
likely putter along at sidewalk speeds. At the road speeds I ride ....

Wait a minute! Are you _purposely_ imitating Fabrizio? ;-)


... braking in a turn on a bicycle begins to overtax the avialable traction.

Looks like physics education isn't what it used to be.

It's not the speed that matters; it's the acceleration. If the total of
your longitudinal plus radial accelerations are within reasonable
limits, you'll have no problems braking in a curve. IOW, you can
certainly brake to a reaonable degree in a turn. Pretending this is
impossible shows you are either _amazingly_ inexperienced, or amazingly
closed-minded.

Or, if you prefer, from the r.b.FAQ (in an article by Jobst Brandt):

"Braking in Corners

Why brake in the turn? If all braking is done before the turn, speed
will be slower than necessary before the apex. Anticipating maximum
speed for the apex is difficult, and because the path is not a
circular arc, speed must be trimmed all the way to that point. Fear
of braking in curves usually comes from an incident of injudicious
braking at a point where braking should have been done with a gentle
touch to match the conditions.

Substantial weight transfer from the rear to the front wheel will
occur with strong use of the front brake on good traction just before
entering the curve. When traction is poor or the lean angle is great,
deceleration cannot be large and therefore, weight transfer will be
small, so light braking with both wheels is appropriate. If traction
is miserable, only the rear brake should be used, because although a
rear skid is recoverable, a front skid is generally not. An exception
to this is in deep snow, where the front wheel can slide and function
as a sled runner while being steered.

Braking at maximum lean

For braking in a curve, take the example of a rider cornering with
good traction, leaning at 45 degrees, the equivalent of 1G centrifugal
acceleration. Braking with 1/10g increases the traction demand by one
half percent. The sum of cornering and braking vectors is the square
root of the sum of their squares, SQRT(1^2+0.1^2)=1.005 or an increase
of 0.005. In other words, there is room to brake substantially during
maximum cornering. Because the lean angle changes as the square of
the speed, braking can rapidly reduce the angle and allow even more
braking. For this reason skilled racers nearly always apply both
brakes into the apex of turns."



Regarding puttering along at sidewalk speeds: Well, we can't really
prove anything without you and I riding side by side, but no, I'm not
considered slow. In fact, without knowing anything about your riding
speed, I wouldn't have any fear of keeping up with you. That comment of
yours was mistaken and foolish.

Yet again.


--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

In article ,
Frank Krygowski wrote:

Nate Nagel wrote:

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.

Seems to me you should _always_ allow a reasonable cushion in your
speed. If you ever find yourself driving at ten tenths on a public
road, you've made a mistake.

Now, mistakes happen. But it's a bit immature to admit your mistake,
describe it in great detail, then try to pass it off as impossible to
avoid. And that's pretty ineffective, too, when others can point out
that they did _not_ make that mistake.

And if you meant the mistake was merely difficult (not impossible) to
avoid - then those who have avoided it have demonstrated greater
competence than you did, haven't they?

The huge mistake is for advisory limits to be set so inconsistently that
one doesn't have an honest idea for what speeds can be used in such
situations.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."