Cities Turning to Bicycles

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."

In article ,
(Nate Nagel) wrote:

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...okTextView/400
9;cs=default;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

It also shows how stupid the system is.

A ball bank indicator? One big problem with it: in addition to the
movement of the ball due to lateral g forces, you also get movement due
to the roll of the vehicle. And since different vehicles roll different
amounts, you automatically get inconsistent results.

--
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."

Alan Baker wrote:

In article ,
Wayne Pein 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.



Such a turn could be designed explicitly for the purpose of slowing
traffic. In that case, a sign can warn of it.

Wayne



An off-ramp from a freeway that has a stop light at the end of the ramp.
One must slow or stop anyway, and the forced slowing with a decreasing
radius geometric additionally sends the message that the road about to
be entered is not a freeway.

Wayne

In article ,
Wayne Pein wrote:

Alan Baker wrote:

In article ,
Wayne Pein 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.



Such a turn could be designed explicitly for the purpose of slowing
traffic. In that case, a sign can warn of it.

Wayne



An off-ramp from a freeway that has a stop light at the end of the ramp.
One must slow or stop anyway, and the forced slowing with a decreasing
radius geometric additionally sends the message that the road about to
be entered is not a freeway.

Wayne

Why not have a constant radius turn of the same radius as your proposed
decreasing radius ramp at its tightest? What would be the disadvantage?

--
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."

Wayne Pein wrote:

Alan Baker wrote:

In article ,
Wayne Pein 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.



Such a turn could be designed explicitly for the purpose of slowing
traffic. In that case, a sign can warn of it.

Wayne




An off-ramp from a freeway that has a stop light at the end of the ramp.
One must slow or stop anyway, and the forced slowing with a decreasing
radius geometric additionally sends the message that the road about to
be entered is not a freeway.

Wayne


Why would you want to do that? I would think that would lead motorists
to misjudge the exit to be safe at a faster speed than if it were a
constant radius the whole way through. I would think the correct ramp
shape would be a constant radius curve, with an "stop ahead" sign over
the advisory speed sign to alert motorists to the signal.

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

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.



google for "friction circle" to see why that's a bad idea (yes, on a
bike too.)

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Alan Baker wrote:

In article ,
(Nate Nagel) wrote:


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...okTextView/400
9;cs=default;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


It also shows how stupid the system is.

A ball bank indicator? One big problem with it: in addition to the
movement of the ball due to lateral g forces, you also get movement due
to the roll of the vehicle. And since different vehicles roll different
amounts, you automatically get inconsistent results.


Maybe *YOUR* car has perceptible roll at under 0.5G G

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Alan Baker wrote:

An off-ramp from a freeway that has a stop light at the end of the ramp.
One must slow or stop anyway, and the forced slowing with a decreasing
radius geometric additionally sends the message that the road about to
be entered is not a freeway.

Wayne


Why not have a constant radius turn of the same radius as your proposed
decreasing radius ramp at its tightest? What would be the disadvantage?


Starting with a larger radius is more consistent with the high speed
entering the off ramp. As speed is lost, the turn can be tighter to
ensure just that.

Wayne