Suburban traffic engineers object to AB 1581 bicycle signal timing
guidance
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Bob Shanteau
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Oct 31, 2009 11:21 PST
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The latest flap about AB 1581 implementation is that the representative
for Northern California cities to the California Traffic Control Devices
Committee (CTCDC), a traffic engineer named Jeff Knowles from the City
of Vacaville, as well as Ron Keith, a traffic engineer from Orange
County <http://www.iterisprojects.com/octec>, are objecting to the
bicycle signal timing guidelines. The bill added Section 21450.5 to the
California Vehicle Code, which has this provision:
***
(c) Cities, counties, and cities and counties shall not be required to
comply with the provisions contained in subdivision (b) [the requirement
to detect motorcycles and bicycles at new and modified actuated traffic
signals] until the Department of Transportation [Caltrans], in
consultation with these entities, has established uniform standards,
specifications, and guidelines for the detection of bicycles and
motorcycles by traffic-actuated signals and related signal timing.
***
Note the language about about Caltrans establishing "uniform standards,
specifications and guidelines" for "related signal timing". In response
to this requirement, Caltrans had UC Berkeley study the amount of time
that bicyclists took to cross intersections, with the intent of finding
the minimum time for the green plus yellow plus all-red for a single
bicyclist starting from a standing start a the limit line when the
signal turned green. This research led to a simple formula: the
bicyclist crossing time is equal to 6 seconds plus the width of the
intersection divided by a final crossing speed of 14.7 feet per second
[10 mph]. At its May meeting, the CTCDC recommended this formula for
inclusion as guidance in the California Manual on Uniform Traffic
Control Devices, which Caltrans did in the form of Traffic Operations
Policy Directive 09-06
<http://www.dot.ca.gov/hq/traffops/signtech/signdel/policy/09-06.pdf>
effective Sept. 10. This guidance goes on to say, "A limit line
detection system that can discriminate between bicyclists and vehicles
may be used to extend the length of the minimum green."
The example given in the background of the recommendation to the CTCDC
was where Park Avenue crosses El Camino Real opposite Stanford
University. That intersection is 125 feet wide, so the crossing time is
15 sec. The current minimum green, yellow and all-red intervals are 7, 3
and 1 sec, respectively. Thus the new minimum green time would need to
be increased by 4 sec. Using the formula results in longer minimum green
times than are commonly used now, but the research team found that the
increased minimum green times would have a minimal effect on traffic
congestion because during periods of congestion the side street green
times are usually longer than the minimum green times anyway. Also, the
time needed to serve pedestrian calls has a much bigger impact on
congestion.
Nevertheless, Jeff Knowles and Ron Keith are objecting to the bicycle
signal timing guidance. They both work in suburban areas where
signalized intersections of 6 or 8 lane arterials with multiple turn
lanes are common. Their objection is that since their detection systems
do not currently differentiate between bicycles and cars, they have to
provide enough time for a single car on a minor movement as though it
were a bicycle and that the extra time will take away from the time for
the major movements, causing the intersections to fail.
Clearly, such wide intersections are not designed to serve bicyclists or
pedestrians and have no place in a modern city. Nevertheless, these
intersections do exist and cannot be ignored. The obvious answer is to
adopt detection methods that differentiate between bicycles and cars,
and development of such methods is under way. Until then, agencies
should realize that the bicycle signal timing guidelines are just that:
guidelines. They are not requirements. If an agency believes that there
is an overriding reason why they cannot provide sufficient time for
bicyclists to cross the street, then they are free to provide less time.
Jeff Knowles and Ron Keith will be asking the CTCDC to weaken the
bicycle signal timing guidance at its next meeting in January 2010 in
San Diego. A couple of years ago, Caltrans agreed to let the California
Bicycle Advisory Committee have an opportunity to provide input to the
CTCDC on bicycle related items, so this item will be on the agenda of
the next CBAC meeting on December 3 in Sacramento. I plan to attend the
CBAC meeting, but right now I do not plan to attend the CTCDC meeting. I
will, however, keep CABOforum updated on this issue.
Bob Shanteau
Transportation Engineering Liaison
California Association of Bicycling Organizations
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