Originally Posted by cyccommute (Post 15780345)

I would not say 'some' jurisdictions set the loops to be less sensitive but would say that all do it to avoid just the problem you detail.

Originally Posted by jputnam (Post 15801222)

Fortunately, in Washington State, that's no longer true -- they're required by law to adjust sensors to detect bicycles. If they want to avoid false positives from adjacent lanes, they need to upgrade their hardware. An extra signal cycle that isn't needed isn't nearly as dangerous as forcing cyclists to make a left turn across oncoming traffic.

Originally Posted by genec (Post 15777327)

No, it won't... but drivers hold to mind many myths. Some driver even think bikes should be on sidewalks. LOL

Emergency lights are triggered either by a special strobe on the emergency vehicle or an RF signal, neither of which is a rush at high speed toward the light.

Originally Posted by cyccommute (Post 15780345)

You have to have the wheels directly over the most sensitive part of the loop. For a figure 8 sensor, that means being directly over the middle wire. For the round detectors, that means being over the wire that leads from the loop to the box. In both cases, those wires are a double wire which increases the sensitivity greatly.

Originally Posted by jputnam (Post 15801222)

[stuff]

Originally Posted by bshanteau (Post 15823954)

You're right about figure-8 loops (technically called quadrupole loops), but not about circular loops. Although it is true that there are "double wires" in the slot leading from the loop to the box, the current in those wires is in opposite directions, resulting in no magnetic field over them. For round and square loops both (which are dipole loops), you need to have your wheels directly over the wire in the loop itself.

Originally Posted by cyccommute (Post 15826216)

I don't agree. A quadrupole loop has the current on the center leg traveling in opposite directions for each of 2 wires that make up that center leg because of the way that the loop is configured. The 2 wires actually increase the sensitivity as opposed to a dipole loop. The magnetic fields are additive and don't cancel each other out. The wires leading from the detection box to a circular loop would work the same way.

Originally Posted by bshanteau (Post 15827798)

Yes, the magnetic field is additive, but it is additive for current in two wires flowing in the same direction (and subtractive for current flowing in opposite direction).

Now apply that principle to quadrupole loops. This is a detail from Caltrans Standard Plan ES-5B showing the winding detail for what they call a Type Q loop:

Loops run on radio frequency AC current, but assume for the moment that the current is flowing in the direction of the S and F arrows. If you follow the the S arrow, you will see that it points up in the left wire, down in the center wire, and up again in the right wire. Thus the current is flowing up in the left and right wires and down in the center wires. The total current in the center wires is double that in the upper and lower wires, meaning that the magnetic field is double also. That is why the center wires are the "sweet spot" for quadrupole loops.

Also, the S and F arrows in the lead-in wires are pointing in opposite directions, making the net current in the lead-in zero.

Originally Posted by bshanteau (Post 15827798)

Yes, the magnetic field is additive, but it is additive for current in two wires flowing in the same direction (and subtractive for current flowing in opposite direction).

Now apply that principle to quadrupole loops. This is a detail from Caltrans Standard Plan ES-5B showing the winding detail for what they call a Type Q loop:

http://bikeforums.net/attachment.php...hmentid=328019

Loops run on radio frequency AC current, but assume for the moment that the current is flowing in the direction of the S and F arrows. If you follow the the S arrow, you will see that it points up in the left wire, down in the center wire, and up again in the right wire. Thus the current is flowing up in the left and right wires and down in the center wires. The total current in the center wires is double that in the upper and lower wires, meaning that the magnetic field is double also. That is why the center wires are the "sweet spot" for quadrupole loops.

Also, the S and F arrows in the lead-in wires are pointing in opposite directions, making the net current in the lead-in zero.

Originally Posted by genec (Post 15828165)

Bob, so are the Quad loops the newest designs?

Originally Posted by bshanteau (Post 15828503)

Not for bicycles, no. There is new language in the California Manual on Uniform Traffic Control Devices that, for all new detector installations, bicycles that are anywhere in the "limit line detection zone", which is a 6'x6' square with its front edge at the limit line, need to be detected.

The only loop configurations that can detect bicycles are diagonal quadrupoles, such as a Caltrans Type D (which was invented by 3M in the 1980's) or a quadracircle (which was invented in Palo Alto in about 1990).

http://bikeforums.net/attachment.php...hmentid=328060 http://bikeforums.net/attachment.php...hmentid=328061



You need to look to see if you can tell which loop is the newest. Look closely at the loop sealant covering the slots. You may be able to see a continuous strip of loop sealant in one direction or the other. I don't see the photo attached to your original post any more, but when I looked at it a few days ago I couldn't see enough detail to tell which strip of loop sealant was continuous. You may be able to tell in person.

By the way, you may want to look at my FAQ entry at traffic loops for the rec.bicycles archive.

Originally Posted by bshanteau (Post 15828503)

Not for bicycles, no. There is new language in the California Manual on Uniform Traffic Control Devices that, for all new detector installations, bicycles that are anywhere in the "limit line detection zone", which is a 6'x6' square with its front edge at the limit line, need to be detected.

The only loop configurations that can detect bicycles are diagonal quadrupoles, such as a Caltrans Type D (which was invented by 3M in the 1980's) or a quadracircle (which was invented in Palo Alto in about 1990).

http://bikeforums.net/attachment.php...hmentid=328060 http://bikeforums.net/attachment.php...hmentid=328061



You need to look to see if you can tell which loop is the newest. Look closely at the loop sealant covering the slots. You may be able to see a continuous strip of loop sealant in one direction or the other. I don't see the photo attached to your original post any more, but when I looked at it a few days ago I couldn't see enough detail to tell which strip of loop sealant was continuous. You may be able to tell in person.

By the way, you may want to look at my FAQ entry at traffic loops for the rec.bicycles archive.

Originally Posted by genec (Post 15828671)

That is largely the problem... as the street wears and gets dirty, it is difficult to tell which loop is newer or active.

The photo in the original post is just representative of what I see from time to time... and this is on regular residential streets. Newer streets with BL do have loops in the BL. But I live in a 60 year old neighborhood.

Fortunately for me the traffic in this area often opens up enough for me to run the light, or a car comes along and triggers it... otherwise this would be a very very annoying problem.

http://bikeforums.net/attachment.php...hmentid=328072

Originally Posted by genec (Post 15828671)

That is largely the problem... as the street wears and gets dirty, it is difficult to tell which loop is newer or active.

Originally Posted by bshanteau (Post 15831044)

In California, the requirement for limit line detection zones kicked in on September 10, 2009, and is now incorporated in the CA Manual on Uniform Traffic Control Devices. After that date, if any substantial changes were made to the detection at a traffic actuated signal, then limit line detection zones are required. Perhaps informing your city staff of that would be helpful.

Here are the relevant definitions in in the CA MUTCD:

QUOTE]104b. Limit Line Detection Zone – a Referenced Bicycle-Rider must be detected in a 6 x 6 feet area immediately behind the limit line, centered either in a normal width lane or if the lane is more than 12 feet wide, centered 6 feet from the left lane line. For a lane of 20 feet or greater, two minimum 6 x 6 feet areas shall constitute the Limit Line Detection Zone.

171a. Reference Bicycle-Rider – a minimum 4 feet tall person, weighing minimum 90 lb, riding on an unmodified minimum 16 inch wheel bicycle with non-ferromagnetic frame, non-ferromagnetic fork and cranks, aluminum rims, stainless steel spokes, and headlight.