Cities Turning to Bicycles

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

In article ,
Nate Nagel wrote:

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...BookTextView/4
00
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

*Every* car does.

--
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."

Nate Nagel wrote:
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.)

It's only a bad idea if you enter the turn at a speed where *all* of
the available traction is used for cornering, i.e. too fast. But since
many turns are entered before the driver can completely see the
turning radius throughout the turn he should always leave sufficient
margin so there is still traction available for braking in addition to
cornering. Fortunately the mathematics of perpendicular vector addition
help us out here. The equation of a circle is x^2 + y^2 = r^2 where we
can use 'x' for the traction available for braking and 'y' for the
traction available for cornering, and 'r', the resultant is the total
available traction. Let's assume the total traction is 1. Then
entering the turn so fast that cornering alone requires a traction of
1.0 would leave nothing available for braking. But entering even a
little slower, say where cornering only requires a traction of 0.9 now
allows us to use some braking up to a traction of sqrt(1-.9^2) = 0.44

Because the forces are perpendicular we can use our brakes up to almost
44% of maximum and simultaneously corner at 90% of maximum without
exceeding 100% of the available traction. Even if the driver (or
cyclist) cuts it closer and is cornering so fast that he's using
95% of the available traction he can still apply the brakes at 31% of
maximum before risking a skid. And even the real thrill-seeker
who corners at 99% still has 14% of maximum braking available to him
before initiating a skid. So yes, the brakes should be applied
carefully and with some caution while cornering, but there is nothing
about "friction circles" (really just basic vector force addition)
that says no braking should be combined with cornering.

I live near a 3500' hill which I frequently ascend and descend on my
bicycle, usually in the company of other cyclists. The road is very
winding and, as is common of many mountain roads, has turns where the
radius of curvature varies. I use my brakes on the way down in
most of the turns and don't think I've ever seen anyone descend this
hill without doing a substantial amount of braking while in the turns.

Nate Nagel wrote:
Frank Krygowski wrote:


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.)

I don't need to google friction circles. I know all about them.

It's interesting that Brent claimed _I_ was talking about racing, i.e.
limit of adhesion situations, now that you are using a term that really
pertains only to that situation.

If a vehicle is not undergoing extreme lateral acceleration, there is
plenty of friction available for braking as well as turning. And, as on
freeway exit ramps, I have sense to stay away from ten-tenths cornering
moves.

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