Just for the record, I'm not condoning illegal behavior, and it the
position of the Bicycle Federation of Wisconsin that ALL road users should
obey ALL the laws ALL of the time.
But I thought many folks on this list would find this essay, co-written by
a physicist, interesting. I particularly liked the last paragraph; perhaps
the suggestion made in it should be part of all future employee contract
negotiations the city undertakes. The city already has the "Bikes at Work"
fleet.
From the Environmental and Architectural Phenomenology Newsletter:
Why Bicyclists Hate Stop Signs
By Joel Fajans & Melanie Curry
http://www.arch.ksu.edu/seamon/Fajans.htm
Environmental & Architectural Phenomenology Newsletter
Why Bicyclists Hate Stop Signs
By Joel Fajans & Melanie Curry
Curry is the managing editor of ACCESS, a transportation journal published
quarterly by the University of California Transportation Center at Berkeley
(UCTC, Berkeley, CA 94720-1782;
<mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED]). Fajans
is a physicist and a professor of physics at the University of California
at Berkeley. He writes: It is curious and a bit depressing that this
essay, along with another on bicycling physics, has attracted far more
attention than any of my real research! (Physics Dept. MS7300, UC
Berkeley, Berkeley CA 94720-7300;
<mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED]). All we EAP
editors can say is were glad you and Curry wrote the piecea fine example
of a kind of hands-on phenomenological research. The essay originally
appeared in the spring 2001 issue of ACCESS (no. 18, pp. 28-31), and we
thank Curry for permission to reprint. © 2001 The Regents of the University
of California.
A commuter has much to consider before leaving for work. What route to
take, considering hills and traffic? What clothes to wear, considering ease
of movement, comfort, perspiration, distance, and weather?
But these questions fade when compared to the safety, speed, and energy
issues bicyclists deal with en route. Transportation planners know that
incorporating bicycles into the transportation system can help ease traffic
congestion by substituting bikes for cars; they also know that mixing cars
and bikes can be tricky.
Seldom, however, do these same planners account for the bicyclists
concernsmatters that dont occur to the typical car-driving planner.
Unless planners take bicyclists concerns seriously, their efforts will do
little to increase the numbers of bicycles or help bicyclists and drivers
coexist safely.
Take a simple stop sign. For a car driver, a stop sign is a minor
inconvenience, merely requiring the driver to shift his foot from gas pedal
to brake, perhaps change gears, and of course, slow down. These annoyances
may induce drivers to choose faster routes without stop signs, leaving the
stop-signed roads emptier for cyclists.
Consequently streets with many stop signs are safer for bicycle riders
because they have less traffic. Indeed, formal bike routes typically
include traffic-calming devices like barriers, speed bumps, and stop signs
to discourage car traffic and slow down those cars that remain.
A route lined with stop signs, however, is not necessarily desirable for
cyclists. While car drivers simply sigh at the delay, bicyclists have a
whole lot more at stake when they reach a stop sign.
Energy Efficiency
Bicyclists can work only so hard. The average commuting rider is unlikely
to produce more that 100 watts of propulsion power, or about what it takes
to power a reading lamp. At 100 watts, the average cyclist can travel about
12.5 miles per hour on the level. When necessary, a serious cyclist can
generate far more power than that (up to perhaps 500 watts for a racing
cyclist, equivalent to the amount used by a stove burner on low).
But even if a commuter cyclist could produce more that 100 watts, she is
unlikely to do so because this would force her to sweat heavily, which is a
problem for any cyclist without a place to shower at work.
With only 100 watts worth (compared to 100,000 watts generated by a
150-horse-power car engine), bicyclists must husband their power.
Accelerating from stops is strenuous, particularly since most cyclists feel
a compulsion to regain their former speed quickly. They also have to pedal
hard to get the bike moving forward fast enough to avoid falling down while
rapidly upshifting to get back up to speed.
For example, on a street with a stop sign every 300 feet, calculations
predict that the average speed of a 150-pound rider putting out 100 watts
of power will diminish by about forty percent. If the bicyclist wants to
maintain her average speed of 12.5 mph while still coming to a complete
stop at each sign, she has to increase her output power to almost 500
watts. This is well beyond the ability of all but the most fit cyclists.
We decided to test these calculations on an officially designated bike
route in BerkeleyCalifornia Street, which is about 2.2.5 miles long and
nearly flat (average grade 0.5 percent). Traffic is very light, which is
nice for cyclists. But California Street has 21 stop signs and a traffic
light. More that two-thirds of the routes 31 intersections require a stop
thats one every 530 feet.
A parallel route, Sacramento Street, runs one block west of California
Street. Sacramento has four lanes of traffic and can be very busy,
especially during rush hours. With cars parked along both sides of the
street, Sacramento has little room for cyclists. But it has only eight
traffic lights along the section parallel to Californias bike route, and
no stop signs. Since, on average, only half the lights will be red, theres
only one stop every 2,800 feet.
One of us (Joel Fajans) found that keeping exertion constant, he could ride
on Sacramento at an average speed of 14.2 miles per hour without straining.
(note1) At the same level of exertion, his speed fell to 10.9 mph on
California if he stopped completely at every sign. Thus Sacramento was
about 30 percent faster that California. By increasing his exertion to a
fairly high level, his average speeds increased to 19 mph on Sacramento and
13.7 mph on California, so Sacramento was then 39 percent faster.
While a drop of a few miles per hour may not seem like much to a car
driver, think of it this way: the equivalent in a car would be a drop from
60 to 45 mph. Because the extra effort required on California is so
frustrating, both physically and psychologically, many cyclists prefer
Sacramento to California, despite safety concerns. They ride California,
the official bike route, only when traffic on Sacramento gets too scary.
These problems are compounded at uphill intersections. Even grades too
small to be noticed by car drivers and pedestrians slow cyclists
substantially. For example, a rise of just three feet in a hundred will cut
the speed of a 150-pound, 100-watt cyclist in half. The extra force
required to attain a stable speed quickly on a grade after stopping at a
stop sign is particularly grating.
Conserving Energy
One way cyclists conserve their energy at stop signs is to slow down but
not stop. A cyclist who rolls through a stop at 5 mph needs 25 percent less
energy to get back to 10 mph that does a cyclist who comes to a complete
stop. Blasting through a stop sign is a bit dangerous (though less
dangerous than it seems because visibility at most intersections is good
from a bicycle, and if the cyclist has slowed to some reasonable speed,
theres typically plenty of time to stop). (note2)
Of course a sensible cyclist will always slow substantially at a stop sign
if theres a car anywhere nearby. But the car-bike protocol at stop signs
is not clear. Drivers (and bicyclist) are unpredictable. Will drivers take
turns with bikes in an orderly way as they do with other cars? Will they
start to go, notice the bicyclist, and suddenly stop again to wait, whether
the cyclist is stopped or not? Will they roll through the stop without
seeing the bicyclist? Will they roll through the stop even thought they see
the bike?
An experienced cyclist knows anything is possible. For example, if she
guessed correctly that the car will wait for her, shell want to start
pedaling again as soon as possible, preferable without having slowed much,
thereby conserving energy and inertia. Indeed, traffic flow is improved
where cyclists do not come to a complete stop, for drivers need not wait as
long for the bikes to clear the intersection.
Clearly, stop signs are tricky for bicyclists. On one hand, they increase
safety by decreasing the number of cars on a road and slowing the remaining
ones. On the other hand, they make cyclists work much harder to maintain a
reasonable speed. For a commuter choosing between a car and a bicycle, the
extra exertion can be a serious deterrent.
Getting Along
Car drivers say they are confused by the presence of bicycles on the road,
and some wish the two-wheelers would just go away. Bicyclists know that
cars cause most of their safety concerns. Traffic planners need to find
ways to help bikes and cars coexist safely.
A good place to begin is by taking the special concerns of bicyclist
seriously, and not assuming that they will be served by a system designed
for cars. Reducing the number of stop signs on designated bike routes would
make bicycle commuting considerably more attractive to potential and
current riders. Allowing bicyclists to treat stop signs as yield signs, as
some states do, could solve the problems in a different way.
Perhaps cities should buy bikes for their traffic engineers and require
that they ride them to work periodically. Theres probably no better way
for them to learn what its like to ride a bike in traffic than actually to
experience its joys and hazards. (note3)
Notes
1. One can keep ones exertion approximately constant by fixing ones heart
rate. For instance, the slower speeds (14.2 and 10.9 mph) were obtained by
maintaining a heart rate of 125 beats per minute (bpm). This is an easy
rate for many cyclists. The faster speeds (19 and 13.7 mph) required a
heart rate of 165 bpm. This high a rate is difficult enough to discourage
commuting at this pace.
2. Because bicyclists can see over the roofs of cars, they can anticipate
the flow of traffic many cars upstream. They cannot see over the roofs of
SUVs, pickups, and vans, however, and the growing number of these vehicles
dramatically decreases riders safety. The problem is compounded by the
increased use of tinted glass, which prevents cyclists from seeing through
the windows to the traffic ahead.
3. For further information, see J. Forester, Effective Cycling (Cambridge:
MIT Press, 1984); F. R. Whitt & D. G. Wilson, Bicycling Science (Cambridge:
MIT Press,1982); and
<http://www.socrates.berkeley.edu/~fajans/Teaching/bicycles.html>http://www.socrates.berkeley.edu/~fajans/Teaching/bicycles.html.
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