copyright 1996, Tracy-Williams Consulting
Rumble Strips: A Growing Threat to America's Cyclists?
by John Williams
Published in Bicycle Forum #14, April 1987
Recently, the Montana
Department of Highways began installing rumble strips on the shoulders of
rural highways. They did this as a test with the intention of installing
more if these proved successful. Rumble strips are devices placed along
the edge of a roadway and are used to wake up sleepy, inattentive or intoxicated
drivers by producing either a noise or a vibration or both. Some are raised
bumps, while others are depressions. They are installed roughly perpendicular
to the direction of travel; some run continuously along the road edge while
others are spaced at 50' or longer intervals.
The new interest in rumble strips seems to be at least partly the result
of a Federal Highway Administration Notice issued in 1986. The text of the
Notice is included at the end of this article. As a cycling organization,
Bikecentennial was naturally concerned when we learned of Montana's experiment
and we alerted our local members. They, in turn, voiced their objections
to the Highway Department, who then reconsidered their previous approach
and issued a Draft Policy on Rumble Strips.
The Draft Policy was a significant step in the right direction, in that
it addressed some of the safety concerns of cyclists and it limited use
of rumble strips to the traffic-side of wide highway shoulders. However,
we were still leery of the whole approach. In preparing our response to
the Draft Policy, we considered the national implications of a heightened
interest in rumble strips and decided to find out what some of the most
progressive cycling states were doing. Here's what we learned:
From Dick Unrein, Bicycle Program Manager of the Oregon Department of Transportation,
we learned that "no rumble strips are used in Oregon at the present
time. The main disadvantages are the reluctance of slow-moving traffic to
use the shoulder area and the potential liability issues from bicycle accidents."
Rick Knapp, Deputy District Director for the California Department of Transportation
District One Office, sent us a copy of CalTrans Policy & Procedure Memo
P78-14, which specifically rejects rumble strip treatments where bicycle
traffic is allowed. It says "Asphalt concrete dikes, raised traffic
bars or other similar devices shall not be placed between the traveled way
and paved roadway shoulders. These devices represent a hazard to bicyclists
and motorists and prevent bicyclists from entering and exiting the shoulder
area." Mr. Knapp was one of the principal authors of the CalTrans Standard,
which was the model used in developing the 1981 AASHTO Guide for the Design
of Bicycle Facilities. He mentioned liability and safety as their primary
concerns with respect to rumble strips.
Paul Graham of the Ohio Department of Transportation said that "Our
shoulder policy specifically states that rumble strips shall not be extended
across shoulders or other areas intended for bicycle travel. The only alternative
that has been tried that I know of is a 'reverse' rumble strip. This is
an indentation pressed into a concrete shoulder. However, this feature happens
to be along a section of I-70, on which bicycles are prohibited to travel
by law. "If you had a wide enough shoulder, you could try installing
rumble strips (or reverse ones) on just the half abutting the lane. That
way, a bicyclist could leave the travel lane if necessary and only hit a
bump or two before coming to the smooth half of the shoulder which would
accommodate bicycle travel. This would provide a good area to travel until
the bicyclist could get back into the travel lane."
S. A. Moon, Locations-Design Engineer for the Washington State Department
of Transportation sent us copies of their Rumble Strip Policy, which was
developed with input from the State's Bicycling Advisory Committee. He mentions
in his letter that "These are being placed and tested in areas of high
numbers of 'run off road' accidents." According to Don Lund of Moon's
office, to date, there are two locations in the State of Washington with
rumble strips, both of which had serious run-off-the-road accident problems.
Further, the Policy states that "where bicycles are of a concern, and
shoulders are six feet or more, leaving a three-foot minimum untextured
strip on the outside edge of the shoulder allows bicyclists to be separated
Alex Sorton, Associate Director of the Engineering Division of the Traffic
Institute, in conversation with the author, suggested that rumble strips
only be used on wide shoulders (eight feet or greater) where there is a
demonstrated history of run-off-the-road accidents. In such situations,
he suggested keeping the rumble strips narrow (perhaps as narrow as one
foot) to maximize the useable width of the shoulder. Mr. Sorton said that
narrow shoulders (four feet wide, for example) would likely not benefit
from placement of rumble strips because, without a recovery area beyond,
a sleepy motorist would be off the road before he or she was able to wake
up and react. Further, he stated that such rumble strips would be potentially
dangerous for cyclists who would be forced to ride in the traffic lane on
high speed roadways.
According to the FHWA Notice itself, "Shoulder-texture treatments are
recommended for use when resurfacing highways with long tangent or monotonous
sections and a history of run-off-the-road accidents. On other sections
of highways with high run-off-the-road accident histories, the FHWA encourages
consideration of these treatments because of their low cost and potentially
high benefit/cost ratios. Where these treatments are installed, the highway
agency should evaluate their effectiveness." It goes on to say, "If
bicycling is desired on the shoulder, the type of treatment and its benefit
should be weighed against the probability that bicyclists will ride in the
traveled way to avoid them. The decision to use a shoulder-texture treatment
or the exact design should be determined on a case-by-case basis."
It further quotes research that has shown that "accident reductions
of 20% were observed on rural Interstate sections with long tangents or
gently curving alignments."
According to the best available car/bike accident study (Cross 1977), rural
roadways tend to be the locations for one of the most serious accident types:
overtaking. Nationwide, roughly 250 cyclists per year are killed and another
1600 seriously injured when a motorist fails to overtake in a safe manner.
Factors in these collisions include: · Narrow roadways without rideable
shoulders · Most often two travel lanes · High speed limits With
these factors in mind, it is easy to imagine rumble strips contributing
to the problem, especially when installed on narrow shoulders. These strips
would force the cyclist closer to the passing stream of high speed traffic.
And, it goes without saying that accidents involving high speed motorists
tend to be fatal for the cyclist.
According to the Background section of the FHWA Notice, "This type
of treatment may be particularly effective when drivers may be drowsy, under
the influence of alcohol, or otherwise inattentive." These are precisely
the situations in which overtaking car/bike accidents happen. For example,
approximately 30% of all drivers involved in overtaking crashes had been
drinking. In many more cases, the motorist involved 'just didn't see the
bicyclist in time.' The accident typically happens after dark, when drivers
are also most likely to be "drowsy". Thus, it seems likely that
a blanket policy of rumble strip treatments would save some lives-drunk
drivers, for example-at the expense of lawfully riding cyclists.
Next, cyclists, like other road users need to cross the roadway at various
places. They do this in order to turn left or to avoid an object in their
path-for example, a disabled car. If cyclists have to pay undue attention
to the roadway itself, in order to avoid crashing on the rumble strips,
this will make it harder to pay attention to traffic. Clearly, anything
that distracts cyclists from the task at hand is hazardous to their safety.
Further, debris tends to accumulate on the highway shoulders. In the "Snow
Belt" after a winter of sanding and plowing, there is often little
more than a narrow strip of clean pavement to the right of the edge line.
Rumble strips just to the right of the edge stripe may well exacerbate this
problem by forcing the cyclists to ride either in the travel lane or off
in the sand and debris.
Even in parts of the country with mild climates, debris tends to accumulate
on the shoulders. Bottles, cans, old tires, mufflersthese are some of the
obstructions found on the extreme right edge of the pavement. Cyclists will
do all they can to avoid these. Our Recommendations With these factors in
mind, we suggest that states looking at rumble strip policies consider the
1. Overall, since rumble strips constitute a hazard for bicycle travel,
they should not be used where bicyclists are allowed. Bicyclists are legitimate
users of the roadways and their safety should not be compromised in an attempt
to solve other problems.
2. When deemed necessary, rumble strips should be only used as FHWA suggested
in their Notice: as a "supplement [to] other activities undertaken
to improve highway safety through special delineation and pavement markings."
In fact, strong enforcement of drunk driving laws (and stiff penalties)
may well do more for run-off-the-road accidents than a blanket policy of
providing rumble strips. Further, since the best results from the use of
rumble strips are only on the order of a 20% reduction, they should certainly
not be the first countermeasure considered when a problem is identified.
3. Highway Departments should only consider rumble strips where there is
a well-documented safety problem rather than as a general practice. This
would mean using rumble strips as specific countermeasures to identified
4. On narrow roadways with shoulders less than eight feet in width, rumble
strips are inappropriate. Their utility is questionable when there is no
recovery area beyond and they seriously jeopardize the safety of all cyclists
using these roadways.
5. Rumble strips should not be used on sections where there are intersections
or driveways. Such sections would tend to happen closer to towns and would
be more likely to have young riders and riders crossing the roadway. These
would tend not to be the places where run-off-the-road accidents occur anyway.
6. Further, we suggest experimenting with rumble strips narrower than three
feet. According to Alex Sorton of the Traffic Institute, the Cook County
Road Department is trying these and we suspect they'd have nearly the same
effect as wider ones AND they would leave more of the shoulder useable.
Further study on this topic is needed.
7. Finally, designers should develop rumble strip treatments that do not
impair the safety of the cycling public. Clearly, accident countermeasures
should not cause accident problems of their own.
TEXT OF THE FHWA NOTICE
U.S. Department of Transportation
Federal Highway Administration Notice
Shoulder Texture Treatments for Safety
N 7560.9 April 28, 1986
Expiration Date: April 28, 1987
1. Purpose: To endorse the use of and encourage implementation of special
shoulder-texture treatments as an effective method of improving highway
safety. Special shoulder-texture treatments can effectively supplement other
activities undertaken to improve highway safety through special delineation
and pavement markings.
2. Background: Several State highway agencies are implementing shoulder-texture
treatments as a countermeasure to reduce run-off-the-road accidents on long
highway sections. Recent research studies, including a study sponsored by
the Federal Highway Administration (FHWA) titled "Effects of Shoulder-Texture
Treatments on Safety," by AMAF Industries, Inc., have concluded such
treatments can be effective in reducing run-off-the-road accidents on long
sections of highway which may be monotonous to drivers. Accident reductions
of 20 percent were observed on rural Interstate sections with long tangents
or gently curving alignments. This type of treatment may be particularly
effective when drivers may be drowsy, under the influence of alcohol, or
otherwise inattentive. The AMAF study found found that with construction
costs reaching as low as $.07 per foot, very high benefit/cost ratios of
up to 50:1 occurred. In another study, Nevada's evaluation of the bituminous
indented strip showed a benefit/cost ratio of 33:1. The Nevada study was
based on over 700 miles installed at a cost of approximately $300 per mile.
3. Current Practices: Shoulder-texture treatments can be implemented on
newly-constructed shoulders, resurfaced shoulders, or on existing shoulders
(either portland cement concrete or bituminous). Descriptions of several
current methods are included in the Attachment to this Notice. Although
no significant maintenance problems have been identified with these treatments,
certain precautions should be taken:
a. In areas requiring snowplowing, raised treatments should not be used
and quality control procedures for depressed or indented treatments should
ensure that the pavement cross slope is not distorted (hence causing a snowplowing
b. Depressed treatments may "silt up" in areas where aggregates
are used for treating "icy road" conditions. Other treatments
may be considered such as surface treatment on bituminous shoulders.
c. Care should be taken to ensure that roadway surface drainage is not affected
by shoulder-texture treatments. An offset from the longitudinal lane-shoulder
joint is recommended to facilitate joint sealing and minimizing surface
d. Design thickness of new shoulders should consider the loss of section
if depressed treatments are used. Information on shoulder design is contained
in FHWA Technical Advisory T 5040.18, Paved Shoulders, dated July 29, 1982.
a. Shoulder-texture treatments are recommended for use when resurfacing
highways with long tangent or monotonous sections and a history of run-off-the-road
accidents. On other sections of highways with high run-off-the-road accident
histories, the FHWA encourages consideration of these treatments because
of their low cost and potentially high benefit/cost ratios. Where these
treatments are installed, the highway agency should evaluate their effectiveness.
b. If bicycling is desired on the shoulder, the type of treatment and its
benefit should be weighed against the probability that bicyclists will ride
in the traveled way to avoid them. The decision whether to use a shoulder-texture
treatment or the exact design should be determined on a case-by-case basis.
5. ADDITIONAL INFORMATION: Additional information is available in a short
slide/audio tape presentation distributed to all FHWA regional and division
offices by memorandum dated May 9, 1985, from the Offices of Implementation
and Highway Safety. The research report number, FHWA/RD-85/027, "Effects
of Shoulder-Texture Treatments on Safety" has been printed and distributed
to all regional and division offices. Copies of the report are available
for official use while the supplies last from the FHWA, Research, Development
and Technological Report Center, HRD-11, 6300 Georgetown Pike, McLean, VA
22101. Additional copies for the public are available from the National
Technical Information Service (NTIS), U.S. Department of Commerce, 5285
Port Royal Road, Springfield, VA 22161. A charge may be imposed for each
copy ordered from the NTIS.
6. CONTACT: Further information can be obtained by contacting the Office
of Highway Safety at (202) 426-2131.
R. Clarke Bennett
Director, Office of Highway Safety
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