A Speed Reduction Strategy in Local Street Systems - Institute of ...

Traffic (ADT) at the five out of six sites in Las Vegas
revealed that three out of five sites reported approximately a
20 to 50 percent reduction in ADT. Two sites recxxded
approximately 5 to 9 percent increase in traffic volumes. The
Kansas City site recorded a slight increase in tmffic volumes.
A study of the test sites in Las Vegas indicated that the trafllc
volume change may be due to other factors besides the
installation of speed humps.
HUMP INSTALLATIONS
The use of humps in the USA, while not as popular as in
England, is still gaining popularity rapidly. In genemi, most
communities in the USA seeking to install humps on their
problem-plagued residential streets, are coming from the
citizens and elected offkials. Engineering and enforcement
officials oftentimes are opposed to smh barriers. However,
under political pressure many cities are installing such humps
and evaluating the results carefully.
The following speed hump characteristics have a direct effect
on whether or not the overall speed in a residential street is
going to be reduced
1. Size of the hump crest height.
2. Length of the hump.
3. Len@ of the roadway.
4. Spacing of humps.
Various tests around the world have more or less standardized
the crest height and the length of speed humps. However, the
spacing between humps has still not been tested objectively
and remains to be an approximation. The basic premise for
de@mining the optimal spacing between speed humps should
include the-following: - - - -
Therefore, the installation of warning sign and the next hump
should consider the approach speed of the vehicles to the
section of roadway where there are a group of humps to be
placed. The rate of deceleration by the road users and rate of
acceleration after encountering a hump are also determinant
factors for optimal spacing of humps.
The advance warning signs are an essential part of the hump
installations. Pavement markings are also quite helpful and
aid the motorists in wqn.ition of the situation.
SIGNIFICANCETESTTNG
The before and after data from various cities as reported in
papers, internal studies and as observed by the authors, all
point to substantial reduction in speeds at the midpoint between
humps as well as overall speed. The following before and
after speed data were used for a signifkance testing using the
“t” test:
City Roadway 85th Percentile
s~
Before
(mph)
(:p;)
Las Vegas, Langtry Dr. 29 23
Nevada
Clarice Ave. 38.12 26
Campbell Dr. Not 27
Available
Bonanza Rd. 34 27
Avalon Rd. 37.5 21.86
1.
2.
3.
4.
Drivers slow down at humps, however, they start
accelerating as soon as they cross a hump to makeup
for their lost time.
The sign for the next hump should be placed at a
point so that it is visible by the driver just about the
time it reaches 25 mph speed or less.
The placement of the sign will make the driver return
to deceleration mode expecting the next hump to
arrive soon.
The placement of the next hump should consider the
distauce a typical car will lraverse at a normal rate of
deceleration to bring the vehicle to a much lower
speed.
-d Dr. 29.02 23.1
I’housand Kelly Rd. 43 30
Oalrs,
California Silas Ave. 38 34
Kansas City, 7oth St. 33 25
Missouri
Farmington Lancaster Dr. 35.5 26
Hills,
Michigau Kendallwood Dr. 35.7 30.3
Hearthstone Dr. 37.4 28.7
The sample means and standard deviations of the before and
after 85th percentile speeds at the above noted locations are
94 Resource Papers for the 1997 International Conference Hz=