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Treatment Descriptions 39
R&T, 2007) Milled continuous shoulder rumble strips are easy to install on existing and new
pavement, maintain the integrity of the pavement structure, and produce more noise and vibra-
tion than other types of rumble strips. (FHWA Safety, 2007)
4.4.4 Speed Effects
At the high-speed intersection approaches tested through NCHRP Project 3-74, rumble strips
produced statistically significant speed reductions at the perceptionresponse time data collec-
tion location, where a mean speed reduction of 1.3 mph (standard error of 0.5 mph) was
observed. At each site, this data collection point was beyond the rumble strips, and about 250 ft
upstream of the intersection. Overall, no statistically significant speed reduction was observed at
the data collection point where the rumble strips were installed or at the accident avoidance data
collection point (roughly 100 ft upstream of the intersections).
Transverse rumble strips have been used with mixed results. On stop-controlled approaches,
transverse rumble strips have repeatedly resulted in more gradual deceleration by drivers and
increased the percentage of drivers making a full stop at the stop sign by about 30%. (Kermit and
Hein, 1962; Owens, 1967; Zaidel et al., 1986; Harder et al., 2001) However, they have also
increased speed variance. (Morgan and McAuliffe, 1997) The research conducted by Owens
found an increase in speed variance on the intersection approach, indicating that some drivers
slowed down more than others.
University of Minnesota research involving a driving simulator concluded that drivers started
to slow down and finish braking at the same time with and without rumble strips, but braking
occurred earlier with rumble strips. It was also found that drivers brake more and brake earlier
with full-width rumble strips than with wheel-track rumble strips. (Harder et al., 2001)
Miles et al. (2005) found that transverse rumble strips produced mostly small changes in traf-
fic operations at both horizontal curve and stop-controlled intersection sites. This research con-
cluded that the treatment was not successful in significantly reducing approach speeds to an
intersection.
4.4.5 Safety Effects
NCHRP Synthesis 191 (Harwood, 1993) summarized 10 before-and-after studies that investi-
gated the safety effectiveness of transverse rumble strips. The synthesis concluded that transverse
rumble strips may effectively reduce crashes, although more rigorous evaluation is needed to bet-
ter understand the safety effects. (Harwood, 1993) However, a 2006 Texas Transportation Insti-
tute (TTI) study found that transverse rumble strips produced marginal safety benefits at best,
only slightly reducing erratic lane movements. The study did note a 46% reduction in shoulder
encroachments. (Miles et al., 2005)
4.5 Longitudinal Rumble Strips
4.5.1 Overview
No test sites provided documented applications for the high-speed intersection treatments
discussed in this section. Longitudinal rumble strips provide audible and tactile warning to
reduce comfortable speed and to minimize off-the-road or crossover crashes. These treatments
can be applied to rural, undivided highways. Design variations are paved, rolled, or milled; raised
or depressed; painted or unpainted; and cluster spacing. Noise, as well as adverse effects for
motorcycles and bicycles, should be considered.
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40 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections
4.5.2 Applicability and Considerations
Like transverse rumble strips, longitudinal rumble strips are raised or grooved patterns
installed on the roadway travel lane or shoulder pavements to warn drivers of an upcoming need
to act. Longitudinal rumble strips are placed parallel to the direction of travel and may be located
in the centerline or along the shoulder. Refer to Section 4.4 for more information on rumble
strips.
Longitudinal rumble strips are most commonly used to reduce head-on, sideswipe, and
run-off-road crashes along roadway segments. The treatment may be a useful speed manage-
ment treatment for high-speed intersections that exhibit these crash patterns. Bicycle and
motorcycle impacts should be considered as the treatment for intersection applications is
designed.
Continuous shoulder rumble strips are the most common type of longitudinal rumble strip.
These are placed on the roadway shoulder to help prevent drivers from running off the road and
are generally used along expressways, interstates, parkways, or two-lane rural roadways. (FHWA
Safety, 2007) Continuous shoulder rumble strips are typically installed with breaks or gaps only
at exits and entrances to ramps and at street intersections or major driveways. This allows driv-
ers and bicyclists to maneuver near the intersections and driveways without having to cross over
the rumble strips.
Centerline rumble strips are placed on either side of the centerline (see Exhibit 4-8), located
either along the width of the centerline pavement markings (see Exhibit 4-9), or extend slightly
into the travel lane (see Exhibit 4-10). Centerline rumble strips are generally installed to reduce
head-on and sideswipe crashes along undivided roadways. Their primary function is to use tac-
tile and auditory stimulation to alert inattentive or drowsy drivers that their vehicles are
encroaching on the opposing lane. Centerline rumble strips may also discourage drivers from
cutting across the inside of horizontal curves.
(Credit: MnDOT, 2004)
Exhibit 4-8. Centerline rumble strips.
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Treatment Descriptions 41
(Credit: Torbic et al., 2004)
Exhibit 4-9. Centerline rumble strips on the centerline
pavement markings.
(Credit: Torbic et al., 2004)
Exhibit 4-10. Centerline rumble strips extending
into the travel lane.
