MAKING SIGNALS DETECT BICYCLES
Many traffic signals do not detect bicycles very well. Here are some tips to improve the
detectability of bicycles:
- First, remember that the signal must finish timing all intervals in phases of the
traffic light cycle that are ahead of yours before changing the light to your phase.
- The green light of a non-actuated phase will not end until its timing is finished.
- The green light of the artery phase of a semiactuated signal will not end until the
proper time in the coordinated background cycle occurs.
- The green light of an actuated phase will not end until no more cars are detected
approaching the intersection, or until the light has been green long enough for the maximum
time feature to operate.
Here are the types of detectors, with remedies:
- Most signals use LOOP DETECTORS:
- A loop detector is a metal detector, like those used for finding cans on the beach.
It detects anything that conducts electricity, including aluminum, but
not composites or fiberglass. Loops are not sensitive to permanent
- Most loops placed at stop lines use "nonlocking presence mode." This means the
metal must stay over the detector until the light turns green. If a bike
stops beyond the loop, the signal assumes it turned right on red and forgets it was there.
- Detectors some distance upstream of the stop line use "locking pulse mode." They
latch when vehicles pass, remembering the actuation until the signal turns green. Then
they unlock, so additional vehicles can extend the green.
- If the speed limit is higher than 30 mi/hr, it is almost impossible for a bike to
actuate a "locking pulse mode" detector while the signal is green and reach it before
the vehicle extension times out. A backup system is usually built into such a system.
The signal usually rests with the "locking pulse mode" phase green when it receives no
actuations from any vehicles.
- Most loop detectors are octagons, diamonds, or rectangles. Usually they are
visible as shapes of sealing tar covering slots where they are buried in the road.
- The loop creates a sensitive zone inside the shape. This zone extends upward in a cone
or pyramid shape, with the base being the loop itself. The most sensitive part is the
center of the shape.
- Hand-hole boxes, lead-ins, and the loop wires themselves are not sensitive.
- If a street is repaved, you have to remember where the loops are.
- Glittery metallic paint can inhibit detection of the painted parts by a loop detector.
The paint "spoils" the flow of current induced in the metal parts. It effectively creates
a "stealth" bicycle. Painting over it does not help.
- Larger loops detect high metal truck beds better. Smaller loops detect bicycles better.
The six foot diameter octagon loops work pretty well on bicycles if adjusted right.
- Some loops have a bicycle detecting "powerhead" at the stop-line end of the loop.
- Loops at intersections on high speed roads are purposely adjusted to reject bicycles,
because they do not belong on the high speed road.
- A large metal part must be over the center of the loop to be detected.
Metal cranks have the best probability of being detected of any part of a bike. Other
usable parts are metal spoked wheels, frames, derailleurs, shift hubs, and kick stands.
- The space between lanes or at the edge of the road is usually not sensitive.
- If the bicycle is not detected, try tilting the frame to expose more metal to the
loop. Tilting a spoked wheel may work too.
- If the bicycle is just barely detected, the detector may drop the call before the
signal reaches your phase. Continuously tilting the bike from side to side may make
detection more reliable.
- A large sheet metal object (a large cookie sheet will do) held horizontally
over the loop will be detected quite well.
- Sometimes a closed loop or hoop of metal works, but it may not activate all sizes
of loop detectors.
- Try mounting two cookie sheets like horizontal wings on either side of the rear hub.
- Radar detectors are white cylinders suspended over lanes. A small cookie sheet
works here. Use it like a mirror to reflect the energy back to the detector. A metal
helmet works too.
- Ultrasonic detectors look like elbow pipe fittings with visors. A small cookie
sheet, a sheet of cardboard, or a large notebook works with these. Again, use it
like a mirror to reflect energy back to the detector.
- Pressure pad detectors purposely require over 300 pounds pressure, to keep kids
from playing with them. Fortunately, they aren't used much anymore. They still
appear on bridges, where metalwork keeps loop detectors from working.
- Television detectors and infrared detectors should have no problem detecting
bicycles, unless the weather is extremely bad. They look like little cameras on poles.
We should be seeing a lot more of these in the future.
- Magnetometer detectors are totally invisible, buried under the pavement. They
require an iron or steel object, or a magnet, to operate them. A strong bar magnet
should trigger them. They are quite rare.
If all else fails, dismount and walk the bike to the near right corner. If a pedestrian
pushbutton exists, push it, wait for the WALK signal, and walk the bike across the
intersection. If not, pedestrians have a legal right to cross carefully against a red signal,
if no vehicles appear to trigger a traffic actuated light after five minutes. Walk the bike
across in this case, yielding to other vehicles.
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