CVV Newsletter Aug-Sep 2003

Bike Sensitive Traffic Signals

Have you ever cycled up to a stoplight that never changes to green for you?  You probably know
that some stop lights give the green to the major flow of traffic and only give the green to the
side street when it detects traffic there.  And you probably know that your bicycle is often not
noticed by the signal control system.

Most of these "demand-actuated" stop lights are controlled by a wire loop in the pavement.  An
electric current in the loop creates an electromagnetic field (EMF) that is affected by the
presence of metal.  When enough metal is detected, the controller starts a timed sequence of
changing the signal lights.  

Some of those loops never register enough EMF difference when a bike comes along, but more
often a bike will be detected if it is stopped in the right spot.  If you can still see the pavement
cuts where the loop is installed you may have good luck by stopping on one of the cuts.  If the
street has been repaved or chip-sealed, you may not be able to tell exactly where the loop is.

What do you do if the light won't change for you when riding your bike?  With any luck, a car
will come along and trigger the change for you.  If not, you might be faced with a long wait or
you might decide to just stop, yield and go when the way is clear.  You may have a "favorite"
intersection where this is always a problem for you.  You may even count on the light not
changing for you and always just plan to yield and go when the way is clear.

What are the consequences of this?  Your yield-and-go may be interpreted by others as
lawlessness if all they notice is a bike running a red light.  This may be bad for the image of
cyclists in our community.  If you are unlucky, a police officer might interpret it as a moving
violation.

If there is a lot of cross traffic, you may be significantly delayed waiting for a gap in traffic or
you may take some risk crossing in a small gap.  The law says you have the rights and duties of a
vehicle operator, but you aren't given the right of a signal-protected crossing like larger vehicles
get.

Another inconvenient and sometimes hazardous trick some cyclists employ is to ride up onto the
sidewalk and press the pedestrian button to gain a green light.  This puts the cyclist in the wrong
lane position to go straight through the intersection or to make a left turn.  Right turning cars
generally don't trigger a signal change, but those right turners can be hazards when you are on
your way to or from the ped button.

The ped button also generally results in a green signal that is long enough for a pedestrian in the
crosswalk, delaying other traffic long after you have pedaled through the intersection.

My two favorite examples of this problem are on 700 North at 1200 East (on the east side of the
USU campus) and on 1400 North at 800 East (north of campus).  In both cases, north-south
traffic gets the green unless east-west traffic is detected.  In both cases, when I am not
accompanied by other crossing traffic, the light sometimes changes for me and sometimes
doesn't.  One feature employed in other states, to assist cyclists in this situation, is to mark the
"sweet spot" in the pavement where you should stop your bike for maximum effect on the EMF.

You'll see these markings in California, Oregon, Idaho and a number of states to the east of us.
Often when the "sweet spot" is marked, the sensor is also calibrated for optimal sensitivity for
bikes.

In some of these other states, they also employ a double loop sensor instead of a single loop. 
Double loops make a more concentrated EM field that is better at sensing the small amount of
metal in a bike while not sensing large amounts of metal like a truck in an adjacent right-turn
lane.

Let me know your experiences and concerns with unresponsive stop lights in Cache Valley.  Is
this troublesome for you?  Which intersections?  How do you deal with unresponsive signals? 
Does it delay you?  Does it add to your risks of cycling?  If you have information or an opinion,
please share them with me at 752-8386 or bob@cc.usu.edu.

Remember: ride visibly, predictably and legally.