Traffic signals are typically either programmed to change according to pre-set
timing or change based on the detection of vehicles on the roadway. At many signals
that are triggered by loop detectors or induction loops in the roadway, the equipment
is not set up to detect a bicycle - it is too light to trigger a response and
make the lights change. Where there is a lot of other traffic to trip the signals,
this may not be an issue. But at low volume intersections, or in off-peak hours,
or in turn lanes (see later) bicyclists can be left stranded unable to change
the lights. As a consequence, many bicyclists have come to anticipate that the
signals will not detect them and do not wait for them to change. This can lead
them to ride out at signal-controlled intersections when motor vehicle traffic
is still crossing.
A good discussion of this and other signal-related issues can be found in Implementing
Bicycle improvements at the Local Level (http://www.bikewalk.org/PDF/chapt9.pdf),
a report prepared for the Federal Highway Administration by the National Center
for Bicycling and Walking.
The guide suggests signals can usually be adjusted to detect bicyclists. The
Florida DOT's bicycle facilities manual (section 4 page 21) describes some of
the ways in which bicyclists can more easily be detected http://www.dot.state.fl.us/safety/ped_bike/handbooks_and_research/bhchpt4.pdf
and the Oregon DOT provides similar advice in its manual. http://www.odot.state.or.us/techserv/bikewalk/planimag/II7f.htm.
Both manuals include the suggestion that agencies may highlight the most sensitive
part of the induction loop for bicyclists with a small bike logo on the pavement.
While this marking has not yet been approved for inclusion in the Federal MUTCD,
a number of states and localities (e.g. the city of Portland, Ore. www.trans.ci.portland.or.us/Traffic_Management/Bicycle_Program/BikeMasterPlan/appenda2.htm#Signal)
have adopted its use and it may appear in an updated version of the MUTCD before
very long. The symbol is included in the AASHTO Guide for the Development of
Bicycle Facilities (page 66).
More information on bicycle signal detection: http://www.bta4bikes.org/info/pubs/lights.html
