There are a few basic types of traffic calming devices that
have different effects on the motoring public. It is important to
understand how each type of device works and its impacts on motorists
and emergency vehicles. The following discussion is divided to explain
each type of device and the associated policies:
A. Horizontal shift and constriction devices.
(1) Horizontal shift devices include traffic circles, chicanes and medians.
Constriction devices include curb extensions, neckdowns and chokers.
Both horizontal shift and constriction devices slow traffic by physically
forcing motorists to maneuver around the devices. The use of landscaping
within these devices not only enhances the aesthetics of the streetscape
but also increases their effectiveness by breaking up the motorist's
line of sight, which reduces the comfortable speed of travel. Therefore,
these devices, when used in conjunction with one another, are effective
for a longer stretch of roadway rather than just in the immediate
vicinity of the device. These devices also tend to have relatively
lower impacts on emergency response times in that the vehicles can
continue to move around the devices without stopping. However, use
of these devices usually requires prohibition of on-street parking
adjacent to the device.
(2) Policies on horizontal shift and constriction devices:
(a)
Policy No. 4: No horizontal shift and constriction devices such
as medians, traffic circles and chokers shall be used as acceptable
traffic calming devices.
(b)
Policy No. 5: Residents fronting the proposed devices must approve
any required parking restrictions.
B. Vertical deflection devices.
(1) Vertical deflection devices include speed lumps, speed humps, speed
tables, and raised crosswalks and intersections. The only vertical
deflection device that is included in this program is the speed lump.
Speed lumps are similar to speed humps, except they are divided into
three lumps with one foot of space between each lump. The space between
the lumps is specifically designed to accommodate the axle width of
fire trucks. All other vehicles with smaller axle widths have to go
over the humps from at least one side of the vehicle. Speed lumps
are typically 12 feet to 14 feet long and three inches high. One of
the concerns associated with speed lumps is the potential increased
noise in the immediate area where the speed lumps are installed because
of braking and accelerating vehicles. It is important that residents
immediately adjacent to the speed lumps concur to their installation.
(2) Policies on vertical deflection devices:
(a)
Policy No. 6: Speed lumps and raised crosswalks are the only
approved vertical deflection devices to be used.
(b)
Policy No. 7: Residents fronting the proposed speed lump or
raised crosswalk must give their approval prior to installation.
C. Diverters, street closures and turn restrictions.
(1) Diverters, street closures and turn restrictions are measures that
alter the existing transportation circulation system. In developing
a solution it is important not to shift the problem to another neighborhood.
Turn restrictions and street closures can cause a tremendous amount
of traffic diversion over a wide area. These types of measures have
impacts that would need to be evaluated in a greater scope than just
within a particular neighborhood. The impacts would include the environmental
impacts due to changing the transportation circulation system. Many
other boroughs have policies that ban or discourage street closures.
For these reasons, diverters, closures and turn restrictions are not
to be used as traffic calming measures. However, the use of diverters,
street closures and turn restrictions may be used outside of this
program and should be evaluated as part of a larger area-wide study
if their use is to be considered.
(2) Policy on diverters and closures:
(a)
Policy No. 8: Diverters, street closures and turn restrictions
shall not be used as part of this program.
D. Stop signs.
(1) Stop signs are not traffic calming devices. Residents, however, often
request stop signs in an effort to calm traffic. Although residents
believe that stop signs will reduce vehicle speeds, studies have shown
that vehicle speeds after the vehicle has passed through the stop-controlled
intersection are as high, and occasionally higher, than without a
stop sign, as motorists try to "make up" time lost at the stop sign.
The acceleration and deceleration near stop signs generate noise and
adversely affect air quality.
(2) Inappropriate use of stop signs also creates significant adverse
impact to emergency vehicles. Emergency vehicles are required to verify
that a stop-controlled intersection is clear of vehicles prior to
entering. Many times this means that the emergency vehicle must nearly
come to a stop. The delay to an emergency vehicle at a stop sign is
similar to that caused by a vertical deflection device.
(3) Stop signs are traffic control devices that should be used when appropriate
to assign right-of-way to conflicting traffic movements, not to calm
traffic. Stop signs should be installed only at locations where conditions
meet established criteria, which has been the past practice of the
Borough. Studies have shown that stop signs that do not meet established
criteria (known as unwarranted stop signs) have a higher violation
rate. Unwarranted stop signs also create disrespect of traffic control
devices in general and affect behavior at other stop-controlled intersections.
It is for these many reasons that unwarranted stop signs are not to
be used in this program.
(4) Policy on stop signs:
(a)
Policy No. 9: Unwarranted stop signs shall not be used as a
part of this program.