######## ***Synthesis of Shoulder Rumble Strip Practices and Policies***

#### 

##### EXECUTIVE SUMMARY

This synthesis provides a review of shoulder rumble strip research and
the rumble strips' crash reduction record. A discussion of shoulder
rumble strips as perceived by the motorist and the bicyclist is followed
by the presentation of results of three nationwide surveys conducted in
2000 of State DOTs regarding shoulder rumble strips. A comparison of
policies, practices and alternative designs is utilized as the basis for
illustrating the components of a bicycle tolerable shoulder rumble strip
policy. Finally, the need for future research is assessed.

##### TABLE OF CONTENTS

[1.0 INTRODUCTION 3](#introduction)

[2.0 LITERATURE REVIEW 4](#literature-review)

[2.1 Previous Research 4](#previous-research)

[2.2 Ongoing and Future SRS Research
6](#ongoing-and-future-srs-research)

[3.0 SRS DESIGNS 7](#srs-designs)

[3.1 Milled SRS 7](#milled-srs)

[3.2 Rolled SRS 7](#rolled-srs)

[3.3 Dimensions and Offset 8](#dimensions-and-offset)

[3.4 Safety Record 9](#safety-record)

[4.0 EFFECT ON DIFFERENT ROADWAY USERS
10](#effect-on-different-roadway-users)

[4.1 The Driver's Experience 10](#the-drivers-experience)

[4.1.1 The Driver and Motor Vehicle Auditory Stimulus
10](#the-driver-and-motor-vehicle-auditory-stimulus)

[4.1.2 The Driver and Motor Vehicle Vibrational Stimulus
12](#the-driver-and-motor-vehicle-vibrational-stimulus)

[4.2 The Bicyclist's Experience 13](#the-bicyclists-experience)

[4.2.1 The Bicyclist and Bicycle Auditory and Vibrational Stimulus
13](#the-bicyclist-and-bicycle-auditory-and-vibrational-stimulus)

[4.2.2 Other Bicyclist's Concerns 14](#other-bicyclists-concerns)

[4.3 Motorcycles 15](#motorcycles)

[4.4 Other Vehicles 15](#other-vehicles)

[5.0 SUMMARY OF SHOULDER WIDTHS AND POTENTIAL SRS PROBLEMS
16](#summary-of-shoulder-widths-and-potential-srs-problems)

[6.0 SURVEY OF STATES' POLICIES AND PRACTICES
17](#survey-of-states-policies-and-practices)

[6.1 Minnesota DOT Survey (February 2000)
17](#minnesota-dot-survey-february-2000)

[6.2 FHWA Survey (Spring 2000) 17](#fhwa-survey-spring-2000)

[6.3 FHWA Survey (September 2000) 17](#fhwa-survey-september-2000)

[7.0 SRS PRACTICES 19](#srs-practices)

[7.1 Skip Pattern 19](#skip-pattern)

[7.2 Transverse Width of SRS 19](#transverse-width-of-srs)

[7.3 Depth of SRS 19](#depth-of-srs)

[7.4 SRS Placement 19](#srs-placement)

[8.0 SRS POLICY 22](#srs-policy)

[8.1 Policy Classification 22](#policy-classification)

[8.2 SRS Installation Warrants 23](#srs-installation-warrants)

[8.3 Recommended Inclusions into any SRS Policy
24](#recommended-inclusions-into-any-srs-policy)

[9.0 PROPOSED RESEARCH 26](#proposed-research)

[9.1 High Priority Research 26](#high-priority-research)

[9.2 Medium Priority Research 26](#medium-priority-research)

[9.3 Low Priority Research 27](#low-priority-research)

[Appendix A 29](#appendix-a)

[Decibel Levels 29](#decibel-levels)

[Appendix B 31](#appendix-b)

[Mn/DOT Survey 31](#mndot-survey)

[FHWA Spring Survey 32](#fhwa-spring-survey)

[FHWA September 2000 Survey 33](#fhwa-september-2000-survey)

[Appendix C 35](#appendix-c)

[Arizona Rumble Strip Policy 35](#arizona-rumble-strip-policy)

[Appendix D 38](#appendix-d)

[Minnesota Rumble Strip Policy 38](#minnesota-rumble-strip-policy)

[Cited References 50](#cited-references)

[BIBLIOGRAPHY 53](#bibliography)

##  

# 1.0 INTRODUCTION

The first shoulder rumble strips (SRS) appeared on New Jersey's Garden
State Parkway in 1955 when 25 miles of "singing shoulders" were
installed in Middlesex and Monmouth counties. The singing shoulder was a
strip of corrugated concrete that produced a sound when driven upon.
These early SRS were later resurfaced into smooth shoulders in 1965. A
more detailed history of SRS usage is provided by Ligon et al. (1) in
"Effects of Shoulder Textured Treatments on Safety."

From the 1960s on, various States have utilized SRS in a variety of
forms. Due to the growing record of documented studies on safety
effectiveness of SRS, an increase in installation on many high volume
roads has occurred in the past ten years. The popularity of SRS has
recently led to their installation on many two-lane rural roadways.

The League of American Bicyclists (LAB) alerted Congressman James L.
Oberstar of safety concerns SRS present bicyclists. In an effort to ease
bicyclists' concerns regarding SRS, the Federal Highway Administration
(FHWA) met with the LAB and Congressman Oberstar. A product of this
meeting was a decision for FHWA to produce a report on current SRS
policies, designs, and usage. While it is documented that SRS are an
effective means of preventing certain types of crashes, FHWA is
concerned about the challenges that SRS present to some roadway users.
Due to this concern, FHWA assigned Science Applications International
Corporation (SAIC) to perform a synthesis regarding SRS practices and
policies.

The following synthesis:

-   Identifies current and near-term SRS research,

-   Reports on the current status of State Department of Transportation
    (DOT) practices and policies, and

-   Highlights areas where further SRS research is required.

# 2.0 LITERATURE REVIEW

## 2.1 Previous Research

Various research and evaluation studies have been performed on SRS since
their conception in the mid-1950s. This literature review focuses on
work performed since 1984.

Higgins and Barbel (2) performed research in Illinois in 1984 regarding
vibration and noise produced by SRS. While it was determined that
outside noise did not significantly vary with different types and
configurations of SRS, it was determined that SRS produced a low
frequency noise that increased the ambient decibel (dB) level an
additional 7 dB over noise levels produced by traffic on normal
pavement. In general, most measured frequencies were between 50 and 160
Hertz (Hz).

Ligon et al. (1) performed chi-squared analyses on before-and-after
accident data for freeways and expressways with SRS in 1985. The
research revealed a 19.8 percent decrease in accidents at test sites
with SRS as compared to a 9.3 percent increase in accidents at control
sites. The researchers concluded that their analyses involving accident
rates did *not* show significant differences when looking at the
following variables on roadways with textured treatment: high ADT versus
low ADT sites; day versus night reduction in accidents; wide versus
narrow shoulder textured treatments; or spaced versus continuous
shoulder textured treatments. The authors recommend the placement of
textured treatments as close to the edgeline as possible on Interstate
shoulder segments as they are resurfaced.

In 1993 Cheng et al. (3) performed a before and after analysis of
1990-1992 crash data on Utah roadways. It was determined that freeways
without SRS experienced a higher rate of run-off-road (ROR) crashes
(33.4 percent) compared to those with SRS (26.9 percent). Additionally,
highway segments with asphalt SRS that were continuous and located near
the travel lane experienced lower accident rates than highway segments
with concrete SRS that were discontinuous (skip pattern) and offset from
travel lane. Also included in the report was an informal survey of 126
cyclists regarding SRS placement, in which 46 percent preferred SRS
placement near the edgeline and 35 percent preferred SRS placement near
the edge of shoulder.

In 1994 Wood (4) evaluated data from the first five Sonic Nap Alert
Pattern (SNAP) projects that were installed on the Pennsylvania
Turnpike. The evaluation showed a 70 percent reduction in drift-off-road
(DOR) crashes and resulted in milled SRS being installed over the entire
length of the Turnpike.

Khan and Bacchus (5) presented economic and safety benefits to
bicyclists derived from highway shoulder use in a 1995 study. The
authors commented that "it is relevant to note that the addition of SRS
improve the benefit-cost ratios considerably because their benefits are
much higher than their costs."

In a follow-up study to the 1994 Wood study, Hickey (6) reviewed the
initial results in 1997 and added traffic exposure in order to compare
accident rates per vehicle-distance-traveled. Additionally, adjustments
were made to account for a decline in all accidents during the study
years. The study revised the initially reported 70 percent crash
reduction to a 65 percent reduction.

Data collected by the New York State Department of Transportation
(NYSDOT) and the New York State Thruway Authority (NYSTA) was utilized
by Perrillo (7) in 1998 to perform a before and after analysis. The
results of the analysis for both agencies revealed at least a 65 percent
reduction in ROR crashes on rural Interstates and parkways due to milled
SRS.

In a 1999 study, Griffith (8) extracted data from California and
Illinois and estimated the safety effects of continuous rolled SRS on
freeways. To perform this study, treatment and downstream freeway
sections were initially analyzed for all fatigued/drowsy crashes. It was
not possible to identify all fatigued/drowsy crashes in this dataset,
therefore, an alternative analysis was performed using
alcohol/drug-impaired drivers as a substitute for fatigued drivers. The
results from this analysis estimated that continuous SRS reduced
single-vehicle ROR crashes on average by 18.3 percent on all freeways
(with no regard to urban/rural classification) and 21.1 percent on rural
freeways.



Moeur (9) tested 28 bicyclists (5 basic, 17 skilled and 6 experienced)
in a 2000 Arizona field study by having them ride over various skipped
SRS sections to determine acceptable skip patterns. It was determined
that 3.7 m (12 ft) skips in ground-in SRS pattern would acceptably
permit bicyclists to cross at high speeds (speeds were assumed to be
between 37-45 kph, (23 - 28 mph)). Either 12.2 or 18.3 m (40 or 60 ft)
cycles for the skip pattern were determined acceptable.

The objective of the Pennsylvania Transportation Institute project
performed in 2000 by Elefteriadou et al. (10) was to develop new SRS
configurations that decrease the level of vibration experienced by
bicyclists while providing an adequate amount of stimulus to alert
inattentive or drowsy drivers. Six configurations were tested by 25
intermediate and advanced bicyclists. The researchers recommended the
adoption of two new "bicycle-tolerable" rumble patterns, one for
non-freeway facilities operating near 88 kph (55 mph) and the other for
those operating at 72 kph (45 mph).

Chen (11) performed an analysis of milled, rolled and corrugated SRS in
1994 at 112 differently location on two Interstates in Virginia. A
portion of the report is devoted an a theoretical analysis of tire drop,
which is used to help determine SRS effectiveness. The analysis showed
that tire drop can be up to 50 times greater for milled SRS than rolled
SRS at a critical speed of 105 kph (65 mph). Chen concluded that milled
SRS were more effective than rolled SRS since they were found to produce
12.5 times more vibrational stimulus and 3.35 times more auditory
stimulus. Finally, it was noted in a survey conducted by Chen that an
increasing number of jurisdictions believe that "rolled rumble strips
have very little effect on trucks."

In 2001, the California Department of Transportation (Caltrans) (12)
performed a study of various SRS designs, as well as five prototypes of
incised or pressed rumble strip configurations. This study was based on
the work done by Elefteriadou et al. (10). Six test vehicles, ranging
from a compact automobile to large commercial vehicles were used to
collect auditory and vibrational data while traversing the SRS. Two test
drivers were asked to subjectively rate characteristic of the various
test patterns, based on the driver's perspective. Finally, 55 bicyclists
of various skill levels and ages volunteered to evaluate the SRS
designs. The recommendation of the study was to replace the existing
rolled SRS design with a milled SRS design that is 300 mm (1 ft) in
transverse width and 8 ± 1.5 mm (5/16 ± 1/16 in) in depth on shoulders
that are at least 1.5 m (5 ft) wide. For shoulders less than this width,
the installation of raised/inverted profile thermoplastic was
recommended.

Outcalt (13) led a research effort in 2001 that compared various styles
of SRS in Colorado. The study's recommendations were based upon the
input of 29 bicyclists as well as vibrational and auditory data
collected in four different types of vehicles. While data was collected
on milled and rolled asphalt SRS and milled concrete SRS, no
recommendations were made concerning concrete SRS. Of the ten styles
tested, those that provided the most noticeable vibrational and auditory
stimuli to the vehicle were rated worst by bicyclists. The milled SRS
with a depth of 9.5 ±3 mm (3/8 ± 1.8 in) on 305 mm (12 in) centers in a
skip pattern of 14.6 m (48 ft) of SRS followed by 3.7 m (12 ft) of gap
was recommended.

## 2.2 Ongoing and Future SRS Research

Table 1 presents on-going and proposed rumble strip research efforts, as
of March , 2001.

Table 1. On-Going and Proposed SRS Research Efforts.

  ------------------------------------------ ------------------ ------------
  Study Title                                Researcher         **Status**

  Rumble Strips along the Center of the      Kansas DOT         On-Going
  Travel Lane                                                   

  Cost Effectiveness of Milled Rumble Strips Georgia DOT        On-Going

  Comparison of Accident Experiences         Michigan DOT       On-Going

  Analysis of Accident Data and Shoulder     Virginia DOT       On-Going
  Rumble Strips                                                 

  Centerline Rumble strips                   Colorado,          On-Going
                                             Connecticut, and   
                                             Maryland DOTs      

  Rumble Strip Directly under the Edgeline   Alaska DOT         On-Going

  Location of Roadway Segments with          Oklahoma DOT       Proposed
  Abnormally High ROR Crashes                                   

  Study of the Effectiveness of Shoulder     Nevada DOT         Proposed
  Rumble Strips in Reducing ROR Crashes                         
  ------------------------------------------ ------------------ ------------

#  3.0 SRS DESIGNS

Currently, SRS of various types, patterns, and designs are used in
almost every State. There are four types of SRS designs: milled, rolled,
formed, and raised; the two that are most common are milled and rolled.
Since these are the predominate types installed, the remainder of this
synthesis will deal with these. The differences between these types of
SRS are installation procedure and shape, which affects the amount of
noise and vibration produced.

## 3.1 Milled SRS

Milled SRS can be placed on either new or existing asphalt or Portland
cement concrete (PCC). A milled SRS is made with a machine that cuts a
smooth groove in the roadway's shoulder. A SRS pattern results when SRS
are repeated at regular intervals, as shown in Figure 1. This type of
SRS modifies the pavement surface and provides for a vehicle's tires to
drop, which creates high levels of vibrational and auditory stimuli.

![](media/image1.jpeg){width="2.85in" height="1.85625in"}

**Figure 1. Milled SRS.**

## 3.2 Rolled SRS

Rolled SRS are pressed into freshly laid asphalt pavement, as shown in
Figure 2. Depressions in the hot pavement are made with a roller that
has steel pipes welded to a drum. Rolled SRS are generally rounded or
V-shaped and produce lower levels of auditory and vibrational stimuli
than milled SRS.

![](media/image2.jpeg){width="2.8506944444444446in"
height="2.1395833333333334in"}

**Figure 2. Rolled SRS.**

## 3.3 Dimensions and Offset

The SRS's transverse and longitudinal widths, spacing and depth can be
modified to vary the amount of vibration and auditory stimuli produced.
However, Isackson (14) noted in a nationwide survey conducted by the
Minnesota DOT (Mn/DOT) that the actual dimension of the SRS varies
slightly from State to State. While specific dimensions will be
discussed in a following section, Table 2 and Figures 3 and 4 show the
layout of a typical SRS:

**Table 2. Standard Dimensions of Milled and Rolled SRS.**

  --------------- -------------------- ------------------ -------------------
  **Dimension**   **Measurement**      **Milled (mm)**    **Rolled (mm)**

  A               Repeat Pattern       approx. 130 (5.1   approx. 130 (5.1
                                       in)                in)

  B               Longitudinal Width   180 (7.1 in)       40 (1.6 in)

  C               Transverse Width     400 (15.8 in)      400 (15.8 in)

  D               Tire Drop            13 (0.5 in)        0.75 (0.03 in)

  E               Depth                13 (0.5 in)        32 (1.3 in)
  --------------- -------------------- ------------------ -------------------

![](media/image3.wmf)

**Figure 3. Standard Measurements of SRS.**

![](media/image4.wmf)

**Figure 4. SRS Tire Drop and Depth Illustration.**

Isackson also noted that the offset of the SRS (with respect to the
edgeline) varies greatly from State to State. While the vast majority of
States offset the SRS between 150 -- 600 mm (5.9 - 23.6 in) from the
edgeline, it is possible to find States that place the strip directly
next to or partially under the edgeline or install them as far away as
900 mm (35.4 in). Assuming a SRS with a traverse width of 305 mm (12 in)
on a 1830 mm (6 ft) shoulder, the recovery area can range from 1525 -
610 mm (60 - 24 in).

## 3.4 Safety Record

Even though alternative SRS designs have been used, evaluation studies
have demonstrated that SRS are effective in preventing ROR crashes.
Table 3, taken from a report by FHWA's Wyoming Division Office posted on
FHWA's rumble strip website entitled "Shoulder Rumble Strips B
Effectiveness and Current Practice" (15), presents additional
evaluations conducted since 1985. The success of SRS appears to have led
several States to require the incorporation of SRS on 3R projects
(reconstruction, rehabilitation or resurfacing) on limited access
roadways.

**Table 3. SRS Studies and Associated Crash Reductions.**

  ------------------------ ------------------------ ---------------------
  **State (date)**         **Roadway Type**         **Percent Crash
                                                    Reduction**

  Massachusetts (1997)     Turnpike, Rural          42

  New Jersey (1995)        Turnpike, Rural          34

  Washington (1991)        Six Locations            18

  Kansas (1991)            Turnpike, Rural          34

  FHWA (1985)              Five States, Rural       20
  ------------------------ ------------------------ ---------------------

note: The FHWA study included Arizona, California, Mississippi, Nevada
and North Carolina.

source: "Shoulder Rumble Strips B Effectiveness and Current Practice"
(15)

# 4.0 EFFECT ON DIFFERENT ROADWAY USERS

Simple auditory and vibrational warnings are known to be an effective
means of providing an urgent message to an operator. Auditory stimulus
have been used for many years by human factors engineers and motor
vehicle design engineers as a warning to alert a driver of an important
situation. More recently, vibrational stimulus has been used in motor
vehicles to provide a warning.

## 4.1 The Driver's Experience

The driver that traverses a SRS typically is doing so as their vehicle
unintentionally veers from the travel lane. This driver may be
inattentive, fatigued, or under the influence of drugs or alcohol. In
any case, the driver experiences both an auditory and vibrational
warning when the vehicle's tires roll over the SRS.

Ideally, when a driver encounters a SRS the desired reaction is to have
them regain their attention and steer back onto the travel lane.
However, depending on the level of the driver's inattention, this
desired reaction may not happen. For a semi-alert driver (e.g., one
changing the radio station) it is believed that the driver will simply
refocus their attention and steer the vehicle back onto the travel lane.
For a driver that is asleep the possibility exists that the reaction to
the SRS could be greatly exaggerated, to the extent of sharply turning
the steering wheel and swerving into the adjacent lane or even off the
roadway. Unfortunately, the frequency of this hypothesized scenario is
unknown; no research has been identified to determine what actions a
driver will take when suddenly awakened while driving. What is known is
that to determine the amount of stimulus required to alert an
inattentive driver is compounded by the fact that different types of
vehicles travel the roadway.

### 4.1.1 The Driver and Motor Vehicle Auditory Stimulus

Table 4 presents common transportation sounds and their associated
decibel levels. As can be seen, the sound level of city traffic measured
from inside a car is 85 dB and is similar to the sound level measurement
of heavy traffic. Perrillo (7) reported that the sound inside an
operating passenger vehicle is approximately 60 dB. The sound level of a
car traveling on a highway could not be found for this synthesis, but it
can be assumed to be comparable to the sound level of freeway traffic,
70 dB (assuming no radio or conversation occurring in the car). Given
these decibel levels, the auditory warning generated by the SRS must be
able to be heard inside the vehicle. A more detailed discussion of
decibel levels can be found in Appendix A.

Table 4. Common Transportation Sounds and Their Associated Decibel Level

  -------- -------------------------- --- -------- --------------------------
  **DB**   **Sound**                      **dB**   **Sound**

  70       freeway traffic                90       Truck

  85       heavy traffic                  95 - 110 Motorcycle

  85       city traffic inside car        110      car horn
  -------- -------------------------- --- -------- --------------------------

source: League for the Hard of Hearing (16)

The auditory warning created as a vehicle passes over a SRS sounds much
like a low rumble to the driver. Typically, the sound produced inside
the vehicle by the SRS is not much louder that the ambient level already
inside the vehicle, and at times may be even less. Therefore, it is
important to determine the level of auditory stimulus required to be
heard inside the vehicle.

One of the most obvious ways to measure the auditory stimulus produced
by a SRS is to measure its loudness. Various researchers have made this
measurement both inside and outside of the vehicle. Higgins and Barbel
(2) reported that when a vehicle traveled over SRS, an increase in the
order of 7 dB over regular road noise was recorded at locations 15 m
(49.2 ft) from the SRS. Additionally, it was determined that peak noise
levels averaged at 87 dB in a cab of a tractor-trailer while the tests
were performed.

In 1988 various SNAP patterns were tested by the Pennsylvania DOT and
reported by Wood (4) in 1994. Auditory measurements were taken inside
test vehicles as they passed over five different milled rumble strips
designs at different speeds. The data revealed that as speed increased,
associated decibel level increased. The test vehicles used were a sedan
passenger car and a dump truck.

In Chen's (11) research, which compared various types of SRS, one
characteristic of SRS that was measured was the loudness of the auditory
stimulus. At speeds of 105 kph (65 mph), milled SRS were measured
between 85 -- 86 dB and rolled SRS were measured at 74 -- 79 dB. The
measurements were taken 61 m (200 ft) from the vehicle. It was further
noted that a 3 dB difference between the milled and rolled SRS was
noticeable to drivers.

More recently, Elefteriadoiu et al. (10) reported sound levels inside
the passenger compartment of a minivan when traversing six different
milled SRS at speeds of 72 and 88 kph (45 and 55 mph). While at the
slower speed, the sound levels increased from an ambient level of 68 dB
to approximately 79 dB. Likewise, at the higher speeds, the sound levels
increased from an ambient level of 65 dB to approximately 81 dB.

The Caltrans study (12) recorded sound levels inside the cabin of
passenger vehicles and heavy trucks with the vehicle's fan and radio off
and all of the windows closed. Testing revealed an increase in average
auditory stimulus ranging from 11.0 - 19.9 dB for passenger cars at test
speeds of 80 and 100 kph (50 and 62.5 mph). Heavy trucks produced a
lower amount of auditory stimulus when measured inside the cabin,
ranging from an average of 1.8 dB - 4.7 dB. However, due to a space
constraint at the testing facility, heavy trucks were only tested at
speeds of 80 kph (50 mph).

Outcalt (13) compared sound levels for vehicles taveling on SRS against
those traveling on smooth pavement at speeds of 88 and 105 kph (55 and
65 mph). The author used a generally accepted 6 dB increase in cabin
sound level as a "clearly noticeable" sound level increase to alert a
motorist. Overall, sound levels were louder for SRS with larger
longitudinal widths.

Table 5 summarizes the five described studies, associated decibel levels
produced, and the location of the measurement.

**Table 5. Decibel Levels Produced by Milled and Rolled SRS.**

+---------+----------------------------+-----------------+------------+
|         | Decibel Level Produced     |                 | Location   |
|         |                            |                 | of         |
|         |                            |                 | M          |
|         |                            |                 | easurement |
+---------+----------------------------+-----------------+------------+
|         | **Milled SRS**             | **Rolled SRS**  |            |
+---------+----------------------------+-----------------+------------+
| Higgens | increase of 7 dB over      |                 | outside    |
| and     | ambient levels             |                 | vehicle    |
| Barbel  |                            |                 |            |
| (2)     |                            |                 |            |
+---------+----------------------------+-----------------+------------+
| Wood    | 74-80 (auto)               |                 | inside     |
| (4)     |                            |                 | vehicle    |
|         | 86 (truck)                 |                 |            |
+---------+----------------------------+-----------------+------------+
| Chen    | 85-86                      | 74-79           | outside    |
| (11)    |                            |                 | vehicle    |
+---------+----------------------------+-----------------+------------+
| Elefte  | 75-84 (@ 72 kph)           |                 | inside     |
| riadoiu |                            |                 | vehicle    |
| et al.  | 78-89 (@ 88 kph)           |                 |            |
| (10)    |                            |                 |            |
+---------+----------------------------+-----------------+------------+
| C       | increase of 12 -- 21 (@ 80 | 14 (@ 80 kph)   | inside     |
| altrans | kph) (auto)                | (auto)          | vehicle    |
| (12)    |                            |                 |            |
|         | increase of 10 -- 19 (@    | 13 (@ 100 kph)  |            |
|         | 100 kph) (auto)            | (auto)          |            |
|         |                            |                 |            |
|         | increase of 2 -- 5 (@ 80   | 5 (@ 80 kph)    |            |
|         | kph) (heavy vehicle)       | (heavy vehicle) |            |
+---------+----------------------------+-----------------+------------+
| Outcalt | increase of approximately  |                 | inside     |
| (13)    | 10 dB over ambient levels  |                 | vehicle    |
+---------+----------------------------+-----------------+------------+

Research performed by Harwood (17) in 1993 determined that by modifying
the repeat pattern of the SRS pattern, the noise level produced could be
changed. Of the repeat patterns tested, 3048 mm (10 ft) patterns
produced the lowest noise levels. When the repeat pattern varied between
1524 mm (5 ft) and 3048 mm (10 ft), the noise levels produced decreased
linearly with vehicle speed. Repeat patterns ranging from 305 -- 915 mm
(1 --3 ft) produced noise levels that varied erratically and were
considered undesirable.

Another method to measure the auditory stimulus produced by SRS is to
determine the frequency produced. The Higgins and Barbel (2) study was
the only research identified that measured the frequency of the sound
produced by SRS. While the SRS tested produced frequencies on the low
end of the scale (80 Hz -- 315 Hz), some high level frequencies in the
area of 1000 Hz were measured. While it was shown that speed has some
effect on frequency, no research has been identified regarding the
effect of SRS dimensions on frequency.

### 4.1.2 The Driver and Motor Vehicle Vibrational Stimulus

The vibrations produced when a vehicle passes over SRS typically begin
at one of the front tires. Vertical and lateral accelerations of the
tire are transferred though the vehicle to its steering wheel, seats,
and floor in the form of vibrations. These vibrations must be gentle
enough so that the driver of a compact car does not lose control but
strong enough that the driver of a sport utility vehicle (SUV) or large
truck is able to feel them. As assortment of vehicle types may encounter
SRS, therefore, most SRS appear to be designed with large trucks as the
design vehicle.

Recent advances in technology have made vibrational measurements much
easier to obtain. Chen (11) developed a theoretical analysis of the tire
drop to establish a measurement of effectiveness of the SRS. It was
hypothesized that to generate adequate auditory and vibrational stimuli,
the longitudinal width of the strip should be large enough for the tire
to drop into the grove. Based on standard SRS dimensions used in
Virginia, Chen concluded that milled SRS perform better than rolled SRS
since the tires only drop to the bottom of milled SRS. Field tests
verified that milled SRS produced greater vibrational and auditory
stimuli than rolled SRS. However, as noted by Elefteriadoiu et al. (10),
Chen's theoretical analysis was based on solid wheels, not elastic motor
vehicle tires.

The study by Elefteriadoiu et al. (10) compared five proposed bicycle
tolerable SRS designs to Pennsylvania's existing pattern. In this study,
a minivan was instrumented to measure vertical acceleration and pitch
angular acceleration. When the accelerations of the five proposed
designs were compared to accelerations of the existing design, it was
determined that the difference was insignificant. No further in-vehicle
vibration tests were performed. The depth of the five proposed designs
ranged from 6.3 -- 13 mm (0.25 -- 0.5 in) while the Pennsylvania
existing pattern had a depth of 13 mm (0.5 in).

Four accelerometers were mounted to the steering wheel of test vehicles
in the Caltrans study (12) to test for vibrational stimulus. A general
trend was found in the vibrational stimulus produced, as the depth of
the SRS increased, so did the amount of vibrational stimulus. An
interesting observation regarding the heavy vehicles at speeds of 80 kph
(50 mph) occurred; when the existing rolled SRS was compared to the
proposed milled designs, the average vibrational stimulus of the rolled
SRS was slightly greater.

Outcalt (13) had a minivan equipped with two accelerometers to measure
vibration. One was installed on the floor just behind the driver and the
other was installed on the steering wheel. Vibrational measurements were
taken at 88 and 105 kph (55 and 65 mph) on both SRS sections and smooth
pavement. Results showed that SRS with larger longitudinal widths
produced greater vehicle vibrations.

## 4.2 The Bicyclist's Experience

Bicyclists nationwide have reported safety problems associated with
rumble strips. A combination of this concern and laws enacted by some
States have led most bicyclists to ride as far to the right of the
travel lane as practicable or on the shoulder.

When traveling on the shoulder, debris covering the shoulder or a
narrowing of the shoulder due to an overpass may force the bicyclist
onto the travel lane. If the shoulder has SRS placed near the edgeline,
then the bicyclist must travel over the SRS to get off of the shoulder.
The accepted useable shoulder width required for a bicycle to travel is
1220 mm (4 ft), as stated by the American Association of State Highway
and Transportation Officials (AASHTO) (18). In instances when a
guardrail or curb may infringe on this width, the generally accepted
practice is to increase this with to 1525 m (5 ft), so the bicyclist may
ride further away from the guardrail and still have an effective width
of 1220 mm (4 ft).

### 4.2.1 The Bicyclist and Bicycle Auditory and Vibrational Stimulus

When considering the combined weight of a bicycle and bicyclist, the
sound a bicycle makes when traveling over a SRS is not loud enough to
cause much of a problem. However, the vibration that is produced is of a
great concern to a bicyclist.

It has been proposed by Chen (11) that the deeper the vertical drop
(depth) of the SRS, the greater the vibrational stimulus provided to the
errant driver. It was shown by Moeur (9) that the larger the depth of
the SRS the more difficult for the bicyclists to retain control of their
bicycle while crossing the strips, even at low speeds. However, Gårder
(19) concluded from a test of milled and rolled rumble strips 12 mm (1/2
in.) deep, which he and 20 others traversed on a bicycle, that there is
no danger if a bicyclist mistakenly crossed a rumble strip.

In the study by Elefteriadoiu et al. (10), the five proposed bicycle
tolerable SRS designs were evaluated by 25 intermediate and advanced
bicyclists. Once again, vertical acceleration and pitch angular
acceleration were measured, as well as having each participant
subjectively rate the proposed designs on comfort and control. Low,
intermediate, and high approach speed, as well as three approach angles
(0°, 10°, and 45°) were tested. When the acceleration measurements were
examined and the subjects' subjective rankings were tabulated, it was
determined that the most tolerable design for bicyclists had a depth of
6.3 mm (0.25 in) and caused the least auditory and vibrational stimulus
for motor vehicles.

Fifty-five bicyclists in the Caltrans study (12) were asked to
subjectively rate the various test strips on comfort and control level.
Participants were allowed to ride over the test strips as many times as
necessary, both alone and in groups. Milled SRS that were not as deep
were favored by the bicyclists when compared to deeper milled SRS. An
additional analysis based upon major demographic variables found three
bicyclist variables to be significant: riding in inclement weather, age,
and whether a bicyclist has ridden on SRS.

Of the 29 bicyclists surveyed in the Outcalt (13) study, 27 used
bicyclists with narrow, high-pressure tires. Bicyclists rated each SRS
design for control and comfort. Overall, the survey concluded that while
bicyclists can navigate 9.5 mm (3/8 in) deep SRS fairly easily, when
grooves are 13 mm (1/2 in) deep or greater, bicyclists may experience
control problems.

### 4.2.2 Other Bicyclist's Concerns

Many bicyclist believe that SRS near the edgeline force bicycles further
from the "sweeping action" of passing vehicles that push debris from the
travel lane. Thus, the bicyclist is forced to ride in heavier debris.
Harwood (17), Moeur (9), and Gårder (19) have commented that shoulders
may at times be covered with debris and have acknowledged a vehicle's
sweeping action; however, no research has been identified to document
the width of the sweeping action based upon vehicular speed or volume.

At the current time there are two ways to deal with shoulder debris. The
first is to have maintenance crews routinely sweep the shoulders. The
second is to place a skip (or gap) in the SRS pattern to allow
bicyclists to cross from the shoulder to the travel lane when
encountering debris, but this does not ensure that debris will not be in
the skip pattern.

In addition to shoulder debris, other dislikes of bicyclists with
respect to SRS are listed below:

-   SRS are appearing on more and more roads that are frequented by
    bicyclists,

-   SRS often appear without warning,

-   SRS that are placed close to an intersection,

-   Different States have different standards and designs, and

-   "Weaving" SRS (poorly installed SRS that are supposed to be in a
    straight line) are difficult for bicyclists to ride near.

## 4.3 Motorcycles

Caltrans has performed a motorcycle SRS evaluation of various SRS
designs. In its study, participants rode over a series of various SRS at
either 88 or 105 kph (55 or 65 mph) or another speed they were
comfortable with and then asked to rate their comfort and control for
each of the SRS traversed. It has also been reported Kansas and
Massachusetts have tested motorcycles traversing rumble strips. While
the composition of the Kansas test group was unknown, the Massachusetts
test group was comprised of the police motorcycle squad. Both test
groups reported noticing the rumble strips, however, they did not feel
out of control.

## 4.4 Other Vehicles

Little information was identified regarding SRS and maintenance
vehicles, such as those used for snowplows operation. It was commented
in telephone conversations with some State DOTs that when travel lanes
are first plowed, snowplow operators may use SRS to help them maintain
their course. However, when plowing the shoulder, drivers have commented
negatively regarding the vibrations caused by the SRS.

It has been suggested that maintenance trucks equipped with snowplows,
wide loads tractor-trailers and other vehicles that typically ride over
SRS may want to have dampening devices installed on the vehicle to
lessen the effect of the SRS. However, at this time no dampening device
in known to exist.

# 5.0 SUMMARY OF SHOULDER WIDTHS AND POTENTIAL SRS PROBLEMS

To summarize the current problem, when the various shoulder widths were
classified into groups, it is apparent that problems appear only under
certain conditions. Table 6 is used to illustrate the various shoulder
widths and potential problems that may exist between bicyclists and SRS.

Even though shoulders that are less than 1219 mm (3.9 ft) do not have
the minimum usable width recommended by AASHTO (18) for bicycle travel,
bicyclists may choose to ride on these shoulders in order to maintain a
maximum distance from passing motor vehicles. Shoulders that are between
1220 -- 1829 mm (4 -- 5.9 ft) have both bicyclists and SRS competing for
the same area. It is not surprising that these shoulders tend to be
where bicyclists have greatest concern. Shoulders over 1830 mm (6 ft)
typically have enough room for both the SRS and bicyclist to maneuver
around most existing debris.

**Table 6. Shoulder Width and Potential SRS Problems.**

  ------------------- ------------- ---------------------------------------
  **Shoulder Width    **Problem**   **Reasoning**
  (mm)**                            

  0 -- 609 (0 - 1.9   No            Shoulder too narrow for SRS or
  ft)                               bicyclist.

  610 -- 1219 (2 --   Yes           Shoulder may be wide enough for SRS or
  3.94 ft)                          bicyclist.

  1220 -- 1829 (4 --  Yes           Shoulder might be wide enough for both
  5.9 ft)                           SRS and bicyclist.

  1830 + (6 ft+)      No            Shoulder wide enough for SRS and
                                    bicyclist.
  ------------------- ------------- ---------------------------------------

# 6.0 SURVEY OF STATES' POLICIES AND PRACTICES

During 2000, three SRS surveys were distributed to every State DOT, two
by FHWA and one by Mn/DOT. A copy of the three surveys can be found in
Appendix B.

While none of the surveys achieved a response rate of 100 percent, every
jurisdiction responded to at least one survey. Table 2A in Appendix B
relates the surveys a jurisdiction responded to. When viewed alone, the
surveys convey a sampling of SRS practices; when combined, the surveys
provide a complete synthesis of SRS practices and policies.

## 6.1 Minnesota DOT Survey (February 2000)

In the process of reviewing their SRS policy, Mn/DOT's Design Standards
Unit conducted an informal survey of State DOTs in order to gain a
perspective on the use of continuous milled SRS. State and FHWA
officials were contacted via e-mail and asked six questions of specific
interest to Mn/DOT regarding their State's SRS policy.

Since the intent was to collect this information in a short (i.e., two
week) time period, follow-up questions were not pursued. The document
compiled by Isackson (14) should be considered a general summary of
milled SRS dimensions and policies nationwide.

Thirty-nine responses (78 percent) were received out of a possible 50.
As previously reported, there is a great deal of consistency regarding
the dimensions of SRS, except for the offset, which varied greatly.
According to the survey, approximately 70 percent of the States use
milled SRS. Twenty-one of the 39 surveyed States have some type of SRS
restriction based upon shoulder width. Fourteen States responded that
they have some type of SRS restriction based upon bicycle history.

## 6.2 FHWA Survey (Spring 2000)

An attempt to identify proposed SRS research/effectiveness studies was
addressed with a survey sent to the FHWA Division Offices in each State
and Washington, D.C. The surveys were either completed by the FHWA
Division Offices or forwarded to the State DOT. Attached to the survey
were summaries of research/evaluation studies (either completed,
on-going, or proposed) that were conducted by eight States.

Twenty-one responses out of a possible 51 were received (41 percent).
Thirteen States reported SRS research either underway or recently
completed in their State. While few States commented on the attached
summaries, many States suggested future paths for SRS research and
evaluation. These responses ranged from long term effects on pavement to
human factors and bicycle studies for optimal SRS dimensions.

## 6.3 FHWA Survey (September 2000)

In order to complete this synthesis, an additional survey was sent to
FHWA Division Offices in each State and Washington, D.C. Once again, the
surveys were either completed by the FHWA Division Offices or forwarded
to the State DOT.

Forty-two responses were received out of a possible 51 (82 percent).
Responses to this survey dealt with bicyclists' rights to travel on
Interstates, controlled access highways, and non-access controlled
roads. Bicycle travel on rural Interstates is allowed in a heavy
majority of Western States but in very few Eastern States. Nationwide,
bicycle travel is allowed on some access control roads while not on
others. It was unclear from the survey responses what characteristics
made a controlled access highways acceptable for bicycle travel.
Finally, each State that responded sent an updated copy of their SRS
policy and standards.

# 7.0 SRS PRACTICES

Numerous SRS designs have been implemented and evaluated by different
States. In review of the various standards and specifications, key
modifications to the standard SRS are now discussed.

## 7.1 Skip Pattern

Originally SRS were placed continuously on the shoulder. More recently
at least ten States have been identified that install SRS in a skip
pattern, such as ten meters with and ten meters without SRS. This design
is intended to allow bicyclists to cross from one side of the strip to
the other without much difficulty while still maintaining the ability to
alert errant drivers.

## 7.2 Transverse Width of SRS

With the exception of one State, all States identified use 3660 mm (12
in) as a minimum transverse SRS width. Arizona (20) was the only State
identified that modifies the width of the SRS, and this modification is
based on right shoulder width. If shoulders on an undivided roadway are
less than 1220 mm (4 ft) in width and SRS are installed, the policy
recommends as a guideline that the right SRS transverse width be 153 mm
(6 in) wide. Additionally, by placing the SRS partially under the
edgeline, Arizona is providing the safety benefit of the SRS while still
providing usable shoulder to the bicyclist.

## 7.3 Depth of SRS

Work preformed by Elefteriadoiu et al. (10) has highlighted the
possibility of using multiple SRS designs in one State. The possibility
exists to examine vehicular traffic to determine if a deeper SRS, which
has been shown to be effective with large vehicles, is required on a
road that does not carry many large vehicles. A shallower rumble strip
may provide adequate stimulus to the inattentive driver of a pickup
truck and be gentler to bicyclists.

## 7.4 SRS Placement

As noted by Isackson (14), an inconsistency exists in determining a
standard offset for SRS placement. The two main theories are to place
the SRS close to the edgeline or close to the edge of shoulder. Most
States are following the practice of installing the SRS near the
edgeline but some States place SRS near the edge of shoulder.

SRS placed near the edgeline allow the remainder of the shoulder to be
utilized by other users, such as bicyclists or pedestrians. This small
offset provides a warning to errant drivers as soon as they leave the
travel lane and generates the largest amount of recovery area for the
errant driver. Furthermore, it also places a warning device between
errant motor vehicles and bicyclists. However, this offset forces the
bicyclist to decide whether to travel in the travel lane (if legal) or
on the right side of the shoulder, which may contain debris.

SRS placed close to the edge of shoulder allow bicyclists to travel
freely between the travel lane and the shoulder. Additionally, it also
allows for the sweeping action of the motor vehicles to clear a larger
section of the bikeable shoulder. The drawback of this large offset is
that it reduces the amount of recovery area available for an errant
vehicle and lessens the SRS's potential safety benefit.

Pennsylvania (21) has a variable offset for SRS placement, even though
it does not modify the traverse width of their SRS from 406 -- 432 mm
(16 -17 in). While their recommended offset is 457 mm ± 12 mm (18 in ± ½
in) from the pavement/shoulder joint, for free (non-limited) access
highways the designer has the flexibility to adjust the offset from
102 - 457 mm ± 12 mm (4 - 18 in ± ½ in). When the offset is designed to
be more than 470 mm (18.5 in), the designer is directed to attach
revised details to show selected offset dimensions accordingly.

Table 7 presents bicyclists' and motor vehicle safety advocates'
perspectives regarding SRS placement. The table emphasizes the fact that
the two groups are on opposite sides when it comes to SRS placement.

**Table 7. SRS Placement Based on Drivers' and Bicyclists'
Perspectives.**

**(for Shoulders 1220 -- 2440 mm (4 - 8 ft) Wide)**

+-----+-------+---------------------------+---------------------------+
| **P |       | **SRS Placement**         |                           |
| ers |       |                           |                           |
| pec |       |                           |                           |
| tiv |       |                           |                           |
| e** |       |                           |                           |
+-----+-------+---------------------------+---------------------------+
|     |       | Near Edgeline             | Near Edge of Shoulder     |
+-----+-------+---------------------------+---------------------------+
|     | Motor | · Large recovery zone     | · Eliminates the recovery |
|     | Ve    |                           | zone                      |
|     | hicle | · Earliest warning for    |                           |
|     | S     | errant drivers            | · Diminished early        |
|     | afety |                           | warning for drivers       |
|     | Advo  |                           |                           |
|     | cates |                           |                           |
+-----+-------+---------------------------+---------------------------+
|     | Bicyc | · Forces bicyclists to    | · Allows bicycles to      |
|     | lists | cross over the SRS        | cross freely into travel  |
|     |       |                           | way                       |
|     |       | · Places warning device   |                           |
|     |       | between cars and bicycles | · Placing bicycle in      |
|     |       |                           | sweep zone                |
|     |       |                           |                           |
|     |       |                           | · Places bicycle closer   |
|     |       |                           | to vehicles               |
+-----+-------+---------------------------+---------------------------+

# 8.0 SRS POLICY

## 8.1 Policy Classification

The SRS policies and practices of 41 jurisdictions were collected in the
September 2000 Survey. After review of the policies, five subjective
categories were created based on the level of detail that the policy
gave to bicyclists and their concerns:

*No SRS or policy.* These jurisdictions do not install SRS. A standard
or spec does not exist.

*No written policy but SRS spec.* These jurisdictions do not have a
formal written SRS policy but they do have a standard or spec detailing
SRS installation. Typically the standard or spec contains notes
regarding installation issues. Some of the jurisdictions in this
category were noted as having unwritten SRS policies.

*Written policy but does not mention bicycles.* The jurisdiction has a
formal, written SRS policy but it does not mention bicycles or a
bicyclist's needs.

*Written policy but only mentions bicycles.* The policy mentions
bicycles but it relies almost entirely on engineering judgment regarding
SRS installation.

*Written policy that deals with bicycles.* A formal, written policy that
was designed in an attempt to address some of the concerns bicyclists'
have with SRS.

Table 8 presents a distribution of the 41 policies that were available
for review, by type of policy.

**Table 8. SRS Policies by Type of Policy.**

+----------------------------------------------------------+-----------+
| **Type of Policy**                                       | #######   |
|                                                          | ## States |
+----------------------------------------------------------+-----------+
| No SRS or policy                                         | 1         |
+----------------------------------------------------------+-----------+
| No policy (written or unwritten policy) but SRS spec     | 14        |
+----------------------------------------------------------+-----------+
| Written policy but does not mention bicycles             | 9         |
+----------------------------------------------------------+-----------+
| Written policy but only mentions bicycles                | 7         |
+----------------------------------------------------------+-----------+
| Written policy that deals with bicycles                  | 10        |
+----------------------------------------------------------+-----------+

According to the surveys, SRS policies of at least seven States are in
the process of being updated. From follow up telephone conversations
with some of these States, it was determined that one of three actions
are being taken with respect to policy update:

-   Awaiting FHWA recommendations,

-   Performing their own SRS research/working with the bicycle
    community, or

-   Awaiting FHWA recommendations and the opportunity to view newly
    revised policies of other States.

Some States that have previously updated their policy, including
California and Wyoming, placed a moratorium on SRS installation while
their policy was under review.

At least eight States have a SRS policy (either written or unwritten) in
which they would install SRS only on roads that prohibit bicycles. While
this is one way to ensure that there will not be a conflict between SRS
advocates and bicyclists, it also limits the number of roadways where
this safety device can be installed.

## 8.2 SRS Installation Warrants

Upon review of the surveys and policies obtained for this synthesis, it
was noted that specific warrants for SRS installation do not exist.
However, numerous States had guidelines, criteria, or recommendations
regarding when to install or not install SRS. The following seven
suggestions were found in at least one State policy.

*Minimum Shoulder Width* -- The suggested minimum shoulder width before
installation ranged from 610 mm (2 ft) in Wyoming (22) to 2438 mm (8 ft)
in New Mexico (23).

*High ROR Crash Location* - Numerous policies mention installing SRS in
high ROR crash locations, but only Ohio (24) provides a threshold (0.25
crashes per million vehicle miles traveled) to help the engineer
identify high ROR crash locations.

*Uninterrupted Length* -- Oklahoma (25) set one of its criteria for SRS
installation to be that they can only be used in locations where driving
may be uninterrupted for a length as calculated by the follow equation,
where length is in miles and design speed is in miles per hour.
$\text{Length} = 1\text{30}\left( \text{DesignSpeed} \right)$.

*Significant Bicycle Usage* - Many policies commented that SRS would not
be installed on roadways with significant bicycle usage, however, no
State provided a threshold to its engineers.

*Minimum Speed Limit* -- Numerous States have recommended a minimum
speed limit of 50 mph on all roads in which SRS are to be installed.

*Fully Controlled Roadways or Roads where Bicycles are Prohibited* --
Many States recommend only installing SRS on roadways where bicycles are
prohibited.

*Rural Roadways Only* -- Numerous States recommend to install SRS only
in rural areas.

## 8.3 Recommended Inclusions into any SRS Policy

Of the States that have provided their SRS policies, two policies stood
out from the rest as model policies.

*Arizona*. Utilizes a skip pattern and different SRS widths based on the
type of roadway and right shoulder width. (20) See Appendix C.

*Minnesota*. Has multiple SRS patterns based on roadway type and
shoulder width. (26) See Appendix D.

The following provisions have been identified in various SRS policies.
They are provided as recommendations for future bicycle tolerable SRS
policies. After each recommendation is the name of one State which
currently uses the provisions. By combining some of the alternative
designs and SRS placement strategies, both SRS and bicyclists can share
shoulders.

-   Provide multiple SRS dimensions based on shoulder width or roadway
    type -- Arizona (20),

-   Provide flexible offset for 1830 -- 2440 mm (6 -- 8 ft) shoulders to
    adjust the offset of the SRS to better address bicyclists' needs --
    Pennsylvania (21),

-   Use SRS in a skip pattern when appreciable bike traffic exists or is
    anticipated and shoulders are less than 2440 mm (8 ft) -- Arizona
    (20),

-   Apply SRS on all roads with a high ROR crash history. (Ohio has set
    a threshold of 0.25 crashes per million VMT) -- Ohio (24),

-   Set shoulder width minimum standards greater for those shoulders
    that have guardrails to ensure an "effective shoulder width" for
    bicycles -- Arizona (20),

-   Keep shoulders free of debris on designated bike routes and/or
    designated high bicycle use areas -- Wyoming (22),

-   Do not install SRS when pavement analysis determines that
    installation will result in inadequate shoulder strength --
    Washington (27),

-   Do not install SRS on: bridges, overpasses, or roads with structural
    re-enforcement -- Washington (27),

-   Do not install SRS in: front of driveways, intersections, suburban,
    urban or residential areas - New York (28),

-   Do not use SRS when strong consideration is being given to using the
    shoulder as a peak travel lane or if construction activity within
    the next year will require the use of the shoulder or if the
    shoulder will be overlaid or reconstructed -- Washington (27),

-   Provide advance warning signs or public service announcements to
    educate the public about SRS use, benefits, and limitations --
    Wyoming (22),

-   Apply SRS 45.7 m (150 ft) upstream on all shoulders approaching a
    bridge overpass or underpass when the shoulder width is reduced or
    eliminated -- New York (28),

-   SRS noise can be offensive to nearby residents. Numerous State DOTs
    have restricted SRS use in residential areas -- Wyoming (22),

-   Provide a map/website for bicyclists that shows road with SRS. (Iowa
    is considering this practice.), and

-   Designate bicycle routes throughout the State. It is suggested on
    these roadways, the shoulders be of adequate width (i.e., 1220 mm (4
    ft)), having signing indicating to drivers that the road is a route
    frequently traveled by bicycles, and attempt to keep the road free
    of debris. However, in the event that ROR crashes become a problem
    on a section of the roadway, the possibility exists for the State to
    install SRS. -- AASHTO (18).

# 9.0 PROPOSED RESEARCH

While much research has been done on the effectiveness of SRS, more
research would be useful. In the following section, needed research has
been assigned to one of three levels: high, medium, and low priority.

## 9.1 High Priority Research

High priority research can be classified into two categories: SRS design
and driver interaction.

Much research has already been done regarding the longitudinal width and
depth of the SRS. Several States, such as California and Pennsylvania
have studied various SRS designs in order to determine which are the
most favorable to bicyclists while still meeting threshold vibration and
auditory requirements set forth by motor vehicles. It is recommended
that future research focus on the SRS's transverse width and offset.
Considering that over the last ten years states have begun to experiment
with narrower widths and variable offsets on newly installed SRS, it is
apparent that the SRS does not require the entire shoulder to remain an
effective safety countermeasure.

Since the SRS's specific intent is to alert errant drivers, research
needs to be performed to determine how an inattentive driver reacts to a
SRS. Evaluation of the driver's reaction time and subsequent reaction
will provide excellent design data that will be used to help design
effective SRS. For example, determining the amount of exposure time a
driver will require to make corrective action will lead directly into
determining a minimum transverse width of the SRS. Additionally, Watts
(29) indicates that a need exists to determine the amount of auditory
stimulus required to alert errant drivers, both those that are awake but
inattentive and those that are drowsy or not awake.

## 9.2 Medium Priority Research

Research into skip patterns of SRS needs to be refined to determine its
effectiveness relative to continuous SRS patterns in alerting drivers.
In order to do this, the skip pattern (and SRS transverse width) must
take into account both errant vehicle speed and trajectory as well as
the speed of bicyclists. While the Mouer study in Arizona has done work
in this area based on the bicyclist's needs, further research is
required regarding the length of the skip and SRS width when using a
skip pattern.

Alternative SRS designs and applications should also be further
investigated. Thus, textured edgelines and chip and seal shoulders need
to be evaluated on both a safety and economic analysis.

Reports from Northern States that experience freeze/thaw cycles have
related instances of SRS increasing the degradation of the pavement.
These reports need to be evaluated to determine whether installing SRS
decreases the expected life of the pavement.

Additionally, a narrow SRS placed in the middle of the travel lane is an
option that merits further attention. As previously reported, these SRS
originally were dismissed as being potentially dangerous to motorcycles
or cause an increase in fatigue to drivers of cars and trucks. However,
this dismissal was based on existing SRS designs and patterns.
Alternative SRS designs may prove that this option is feasible and will
not cause difficulty for motorcyclists.

## 9.3 Low Priority Research

Low priority SRS research can be viewed as helping to fill-in the gaps
in current SRS knowledge.

Further investigations are needed to determine the effectiveness of SRS.
Most studies to date have been based on data from Interstates. Now that
data are available on full-access roads where bicycles are allowed to
travel, research should be conducted on these roads and should include
the type of vehicle involved in the crash, time of day, day of week and
time of year.

-   Substitution of raised pavement markers (RPMs) or Botts Dotts for
    SRS,

-   Maximum vibrational threshold for bicycles,

-   Minimum (acceptable) width of shoulder for bicycle travel,

-   Angle of ROR crashes to aid in the proper design of transverse
    width,

-   Method to determine prioritization of existing shoulders for SRS
    retro-fit,

-   Width of sweeping action of vehicles,

-   Minimum width required for a "weave" maneuver required for a
    bicyclist to weave around a SRS (assuming a skip pattern),

-   Noise pollution created by SRS,

-   Cost effectiveness of the skip pattern, and

-   As Intelligent Transportation Systems (ITS) technologies advance,
    further research into the advancement of lane departure warning
    systems and their economic viability will need to be investigated.
    Systems such as these would provide the opportunity to replace SRS.

Appendices

# Appendix A

## Decibel Levels

The loudness of sound is expressed as a ratio comparing the sound to the
least audible sound. The range of energy from the lowest sound that can
be heard to a sound so loud that it produces pain rather than the
sensation of hearing is so large that an exponential scale is used. The
lowest possible sound that can be heard is called the threshold of
hearing. The sound level at the threshold of hearing is:

I~o~ = 10^-12^W/m^2^

Intensity of sound is measured in Watts per square meter. To calculate
the intensity level in decibels, find the ratio of the intensity of
sound to the threshold intensity. Since an exponential scale is being
used, you will find the logarithm of the ratio. If you stopped at this
point the intensity level would be expressed in Bels. This unit was
named in recognition of Alexander Graham Bell. To express the intensity
level in dB (decibels) multiply the logarithm of the ratio by 10. The
resulting equation is:

β = 10∙log(I/I~o~)

Experts agree that continued exposure to noise above 85 dB over time,
will cause hearing loss. To know if a sound is loud enough to damage
your ears, it is important to know both the decibel level and the length
of exposure to the sound. In general, the louder the noise, the less
time required before hearing loss will occur. According to the National
Institute for Occupational Safety and Health (1998), the maximum
exposure time at 85 dB is 8 hours. At 110 dB, the maximum exposure time
is one minute and 29 seconds.

Table 1A. Common Sounds and Their Associated Decibel Levels

  -------- --------------------------- --- -------- ---------------------------
  **dB**   **Sound**                       **dB**   **Sound**

  0        Softest sound a person can      95-110   Motorcycle
           hear                                     

  60       Normal conversation             110      Shouting in ear

  70       Freeway traffic                 110      Leafblower

  80       Ringing telephone               110      Car horn

  85       Heavy traffic                   117      Football game (stadium)

  85       City traffic inside car         130      Stock car races

  90       Truck                           150      Firecracker

  90       Shouted conversation            170      Shotgun

  90       Train whistle at 500 ft         194      Loudest sound that can
                                                    occur
  -------- --------------------------- --- -------- ---------------------------

Taken from:

"Physics Tutorials; Sound; Decibel Levels" Online Posting:
http://www.memphis-

schools.k12.tn.us/admin/tlapages/sound_decibel.htm. October 2000.

"Noise Center; Noise Levels in our Environment Fact Sheet" March 1999.
Online Posting: http://www.lhh.org/noise/decibel.htm. October 2000.

# Appendix B

## Mn/DOT Survey

Question 1: What state do you represent?

Question 2: Does your state use continuous milled shoulder rumble strips
on: (Urban and/or rural - Freeways, Expressways, and/ or Two-lane
Roads)?

Question 3: Do you have any restrictions on usage (Accident Rates,
Shoulder Widths, Bicycle Usage)?

Question 4: Has the bicycle community expressed concern about your
design or use of rumble strips? If so, how has your design and/or policy
changed?

Question 5: What are the dimensions of the milled shoulder rumble strips
that you use?

Question 6: Have you ever installed intermittent milled rumble strips on
a bituminous shoulder? If so, please explain.

## FHWA Spring Survey

Question 1: What comments do you or your State have on the research and
evaluation studies identified in the attachment?

Question 2: What other research or evaluation studies are underway or
have been completed in your State?

Question 3: What further research or evaluation studies do you believe
are needed regarding shoulder rumble strip design and evaluation?

## FHWA September 2000 Survey

Question 1: By State law, are bicyclists allowed on any Interstate
routes? Please be specific, i.e., all, rural sections only, rural
sections with no parallel alternative routes, only where permitted by
signs, none, etc. Is this usage restricted to shoulders only, or may
bicyclists ride in a travel lane? Are any roadway speed limits (maximum
or minimums) regarding when bicyclists are permitted on the shoulders or
traffic lane?

Question 2. Same as above for other controlled access highways such as
freeway, expressways, and parkways\...

Question 3. Same as above for non‑access controlled roads and
streets\...

Question 4. Does your State highway agency have a written policy and/or
design for the use of shoulder rumble strips, and particularly that
addresses bicyclists' concerns? If yes, please fax or mail a copy of
that policy.

Table 2A. Survey Responses by Survey and State.

<table>
<colgroup>
<col style="width: 13%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 3%" />
<col style="width: 13%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 3%" />
<col style="width: 13%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 5%" />
</colgroup>
<tbody>
<tr class="odd">
<td><strong>State</strong></td>
<td><blockquote>
<p><strong>Mn/DOT</strong></p>
</blockquote></td>
<td><blockquote>
<p>Spring FWHA</p>
</blockquote></td>
<td><blockquote>
<p><strong>Sept. FHWA</strong></p>
</blockquote></td>
<td></td>
<td><strong>State</strong></td>
<td><blockquote>
<p><strong>Mn/DOT</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Spring FWHA</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Sept. FHWA</strong></p>
</blockquote></td>
<td></td>
<td><strong>State</strong></td>
<td><blockquote>
<p><strong>Mn/DOT</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Spring FWHA</strong></p>
</blockquote></td>
<td><blockquote>
<p><strong>Sept. FHWA</strong></p>
</blockquote></td>
</tr>
<tr class="even">
<td>Alabama</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Kentucky</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>N. Carolina</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Alaska</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Louisiana</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Ohio</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Arizona</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Maine</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Oklahoma</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Arkansas</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Maryland</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Oregon</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>California</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Mass.</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Penna.</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Colorado</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Michigan</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Rhode Isl.</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Connect.</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Minnesota</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>S. Carolina</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Delaware</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Missouri</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>S. Dakota</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>D. C.*</td>
<td>n/a</td>
<td></td>
<td></td>
<td></td>
<td>Mississippi</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Tennessee</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Florida</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Montana</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Texas</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Georgia</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Nebraska</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Utah</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Hawaii</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Nevada</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Vermont</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Idaho</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>New Jersey</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Virginia</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Illinois</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>New Mex.</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Wash.</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Indiana</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>N. Hamp.</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>West Virg.</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td>Iowa</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>New York</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Wisconsin</td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td>Kansas</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>N. Dakota</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td>Wyoming</td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>

\* The District of Columbia was not contacted in the Mn/DOT survey.

Of the 51 jurisdictions responding to the surveys, only the District of
Columbia does not install shoulder rumble strips.

# Appendix C

## Arizona Rumble Strip Policy

Typical drawings of the Arizona rumble strip can be obtained on the
Arizona DOT website by following the link below and then selecting
section 480 (Continuous Longitudinal Rumble Strips)

http://www.dot.state.az.us/ROADS/traffic/pgp.htm

  -----------------------------------------------------------------------
  **480 CONTINUOUS LONGITUDINAL RUMBLE STRIPS**

  -----------------------------------------------------------------------

480.1 **[INTRODUCTION]{.underline}**

The purpose of this policy is to define when and where continuous
longitudinal rumble strips may be applied on the state highway system.

The purpose of continuous longitudinal rumble strips is to enhance
safety by preventing run-off-road (ROR) collisions with fixed object and
rollovers due to driver over-correction type crashes. These rumble
strips are intended to alert drivers by creating a audible (noise) and
tactile (rumble or vibratory) warning sensation that their vehicle is
leaving the traveled way (traffic lane) and that a steering correction
is required. Before and after accident studies have indicated that ROR
type crashes may be reduced significantly by the use of continuous
longitudinal rumble strips.

480.2 **[POLICY]{.underline}**

Continuous longitudinal ground-in rumble strips may be applied to the
mainline roadway on projects per the recommendations and requirements of
this document.

The following table should be used as a guideline in determining the
groove width of the rumble strips to be installed:

+-----------------------+-----------------------+-----------------------+
| Type of Roadway       | Right Shoulder Width  | Groove Width          |
|                       |                       |                       |
|                       |                       | [(both                |
|                       |                       | sh                    |
|                       |                       | oulders)]{.underline} |
+-----------------------+-----------------------+-----------------------+
| Undivided             | less than 4'          | 6"                    |
+-----------------------+-----------------------+-----------------------+
| Undivided             | greater than or equal | 8"                    |
|                       | to 4'                 |                       |
+-----------------------+-----------------------+-----------------------+
| Divided               | less than 6'          | 8"                    |
+-----------------------+-----------------------+-----------------------+
| Divided               | greater than or equal | 12"                   |
|                       | to 6'                 |                       |
+-----------------------+-----------------------+-----------------------+

For divided roadways, the groove width for the left shoulder of the
roadway should be the same as the width applied to the right shoulder,
where possible.

On undivided two lane highway with shoulders four (4) feet and greater
in width, longitudinal rumble strips should be applied. The use of
longitudinal rumble strips on shoulders less than four (4) feet may be
considered on a case by case basis when supported by a written traffic
evaluation.

On divided highways, longitudinal rumble strips should be applied on the
right (outside) shoulders with a width of four (4) feet or more and on
left (median) shoulders which have a width of two (2) feet or more. The
use of longitudinal rumble strips on divided highways with narrower
shoulders than those noted may be considered on a case by case basis
when supported by a written traffic evaluation.

**The use of longitudinal rumble strips on all roadway shoulders less
that six (6) feet wide with sections of guardrail and/or barrier shall
be evaluated. The effective clear width of the shoulder in these areas
if a continuous longitudinal rumble strip is installed shall be
determined.** The effective clear shoulder width is defined as the
distance between the outside edge of the proposed rumble strip and the
front face of the guardrail or barrier.

The effective clear shoulder width is important for the following
reasons:

(a) Constructibility- To allow for installation equipment, i.e.
    grinding, a minimum effective clear shoulder width of two (2) feet
    is needed from the outside edge of the rumble strip groove to the
    front face of the barrier or guardrail. If the barrier is on a sharp
    curve additional width may be needed. This constructibility issue
    applies to all shoulders and all types of highways.

(b) Bicycle Traffic- If appreciable bicycle traffic exists or is
    anticipated then a minimum effective clear shoulder width of
    three-feet and five-inches (3'-5") should be provided from the
    outside edge of the rumble strip groove to the front face of the
    barrier or guardrail. If this clear area cannot maintained then a
    change of configuration and/or deletion of the rumble strip should
    be considered.

If these minimum clear shoulder width dimension criteria cannot be
maintained, then there are four possible solutions that may be
considered. These possible solutions should be considered in the order
that they are presented here. The first solution is to reevaluate lane
widths; if the lanes are wider than 12 feet it may be permissible to
reduce their width. The second solution is to move the location of the
rumble strip closer to the traveled way and /or use a narrower strip
width (6 inch or 8 inch). If the strip is moved closer to the traveled
way it shall not infringe on the actual traffic lane. The third solution
is to consider using an alternative rumble strip treatment such as
profile pavement markings and/or raised pavement markers; this solution
only applies to non-snow removal areas. The fourth solution is to omit
the use of the longitudinal rumble strip in the area of the guardrail or
barrier.

**Details for rumble strip configuraion and placement shall be shown on
the plans.** Typically the details will be included in conjunction with
project striping plans. **In addition, the limits of the various type of
improvements shall be indicated on the plans.**

Where appreciable bicycle traffic exists or is anticipated on
non-access-controlled highways with shoulders less than eight (8) feet,
the provision of a 10-foot gap for bicyclists to traverse the rumble
strip treatment may be provided. For such situations, the rumble strip
pattern shall consist of 30-foot long segments of rumble strips at
12-inch centers, with 10-foot segments of no rumble strips, on a 40-foot
cycle.

Generally, continuous longitudinal rumble strips should not be applied
on the shoulders of roadways within developed and urban areas. In
suburban and developing areas, the design team should decide whether
rumble strips are appropriate. These types of rumble strips can produce
noise that may be objectionable to citizens that reside nearby. The use
of continuous longitudinal rumble strips in urban areas should only be
considered if there are no other reasonable alternatives and/or it is to
mitigate a specific area problem.

480.3 **[OTHER CONSIDERATIONS]{.underline}**

Continuous longidinal rumble strps may be achieved through a number of
different techniques and patterns (e.g. formed rumble strip, raised
pavement markers like ceramic buttons, or profile pavement markings).
This policy is not intended to restrict or prohibit the use of any of
these other alternatives. If an alternative technique is shown to offer
an advantage over the ground-in rumble strip, then its use may be
pursued.

Ground-in rumble strip can be installed in portland cement concrete
pavement (PCCP). However, at the writing of this policy it still has not
been done in Arizona. Grinding of PCCP requires a diamond tip saw blade
grinding drum that is water cooled. The grinding of asphaltic cement
pavement (ACP) can be done with a steel grinding drum without water
cooling. Thus, doing PCCP ground-in rumble strip would require a
significantly different operation and payment structure than what is
currently reflected in ADOT's ACP grinding practice. Careful study needs
to be given prior to the application of ground-in rumble strip on PCCP.

The make-up of the new pavement or the thickness, condition, and type of
existing pavement needs to be determined prior to the application of
ground-in rumble strip. The installation of ground-in rumble strip on
pavement that is of questionable thickness, condition, or type (e.g. AC
over PCCP) needs to be evaluated to ensure that the installation of the
rumble strip will be possible without adverse impact to the pavement or
the performance of the strip.

This policy or the rumble strip standard drawings do not account for all
possible applications (e.g. rural gore areas). Therefore, it may be
necessary for the designer to develop special application plans or
details for the application of ground-in or alternative longitudinal
rumble strip treatments. **All such plans and details shall be submitted
to the Traffic Engineering Group for review prior to their use on a
project.** This includes the use of centerline rumble strip on two-way
highways.

480.4 **[WRITTEN TRAFFIC EVALUATION]{.underline}**

The use of continuous longitudinal rumble strips on roadways with
shoulders less than four (4) feet shall require a written traffic
evaluation approved by the Manager of the HES Section.

# Appendix D

## Minnesota Rumble Strip Policy

![](media/image5.png){width="1.261111111111111in"
height="0.8527777777777777in"}
![](media/image6.png){width="0.7097222222222223in"
height="0.7013888888888888in"}

######### MINNESOTA DEPARTMENT OF TRANSPORTATION

**Program Support Group**

**Technical Memorandum No. 00-08-DS-01**

**May 9, 2000**

> **TO:** Distributions 57, 612, 618, 650
>
> **FROM:** Patrick C. Hughes
>
> Director, Program Support Group
>
> Assistant Commissioner
>
> **SUBJECT:** Rumble Strips on Shoulders of Rural Trunk Highways

##### EXPIRATION

> This Technical Memorandum supersedes Technical Memorandum 99-15-DS-01
> and Section 4-4.0 of the Road Design Manual. It will be in effect
> until December 24, 2005,
>
> or until included in the Road Design Manual, which ever comes first.

##### Implementation

> This policy shall be in effect for all projects with a scheduled
> letting date after July 1, 2000. District personnel should make every
> effort to implement this policy for projects which have been let prior
> to July 1, 2000 and on which rumblestrip construction has not yet
> begun.

##### Introduction

##### 

> This Technical Memorandum establishes a policy for placement of rumble
> strips on shoulders of rural, state-owned highways. Rural is defined
> as roadway segments that
>
> have minimal residential or commercial development and little or no
> further development is anticipated in the near future.

##### Purpose

> To provide rumble strips to reduce run-off-the-road (ROR) accidents
> and to guide motorists during snowy conditions when striping
> visibility is poor.

##### Guidelines

> Rumble strips shall be placed on all rural highway projects where
> shoulders are constructed, reconstructed, or overlayed and where the
> posted speed limit is 50 mph (80 kph) or greater. This applies to both
> multi-lane and two-lane highways with shoulders 6 feet (1.8 m) or
> greater in width. They shall also be placed on the left shoulder of
> multi-lane roads. Districts should also consider placing rumble strips
> on inplace shoulders at locations with a high ROR accident rate and on
> which no reconstruction is scheduled in the near future. The District
> Materials Engineer should make recommendations regarding the
> structural adequacy of inplace shoulder to receive rumble strips.
>
> Types and applications of rumble strips can be found in Table 1. See
> Figures 1 and 2 for section and plan views of rumble strips on
> bituminous shoulders. The intermittent pattern is shown in Plan View B
> in Figure 2. Figure 3 gives section and plan views of structural
> rumble strips in concrete pavement that have been modified for safety.
> Guidelines for appropriate breaks in the rumble strips due to
> entrances, turn lanes, acceleration lanes, intersections, and
> deceleration lanes on all roads can be found in Figure 4. Rumble
> strips in bituminous shoulders should be produced by the milling
> method. Districts may fog seal rumble strips milled into bituminous
> pavement.
>
> Shoulder widths of 4 feet (1.2 m) or less with rumble strips will not
> adequately accommodate bicycles. Therefore, rumble strips should not
> be placed on these roadway sections unless the District Traffic
> Engineer has documented a serious ROR accident problem and little or
> no bicycle traffic is expected. Districts shall contact the State
> Bicycle Coordinator to determine the amount of bicycle traffic on a
> roadway.
>
> Because rumble strips will require bicycles to ride farther out from
> the vehicle induced wind sweep shoulder edge, brooming may be
> necessary to remove debris to safely accommodate the bicyclist in bike
> use areas.

Technical Memoradum No.: 00-08-DS-01

May 9, 2000

Page 2

> TABLE 1 B Types and Applications of Rumble strips

+----------------------+-----------------------------------------------+
| ####### Applications | > **Rumble Strip Types**                      |
+----------------------+-----------------------------------------------+
| > Freeway right      | > ***Type 1A - 1\' 4" (400 mm) Continuous***  |
| > shoulders^1^       | >                                             |
|                      | > Continuous milled rumble strips used on     |
|                      | > bituminous shoulders that are 1\' 4" (400   |
|                      | > mm) wide and located 2' (600 mm) from       |
|                      | >                                             |
|                      | > the painted edge-line (see Figures 1 and    |
|                      | > 2).                                         |
+----------------------+-----------------------------------------------+
| > Freeway left       | > ***Type 1B - 1\' 4" (400 mm) Continuous***  |
| > shoulders^1^       | >                                             |
|                      | > Continuous milled rumble strips used on     |
|                      | > bituminous shoulders that are 1\'4" (400    |
|                      | > mm) wide and located 4" (100 mm) from the   |
|                      | > painted edge-line (see Figures 1 and 2).    |
+----------------------+-----------------------------------------------+
| > Two-lane roadway   | #####                                         |
| > shoulders (left    |                                               |
| > and right)         | ##### Type 2 - 1\' (300 mm) Intermittent      |
|                      |                                               |
|                      | > Intermittent milled rumble strips used on   |
|                      | > bituminous                                  |
|                      | >                                             |
|                      | > shoulders that are 1\' (300 mm) wide and    |
|                      | > located 4" (100 mm) from the edge-line.     |
|                      | > Intermittent rumble strips shall be milled  |
|                      | > in a 60' (18 m) cycle. (48' (14.4 m) of     |
|                      | > rumble strip followed                       |
|                      | >                                             |
|                      | > by a 12' (3.6 m) gap as shown in Figures 1  |
|                      | > and 2).                                     |
+----------------------+-----------------------------------------------+
| > Multi-lane roadway |                                               |
| > right shoulders    |                                               |
+----------------------+-----------------------------------------------+
| > Multi-lane roadway | #####                                         |
| > left shoulders     |                                               |
|                      | ##### Type 3 - 1\' (300 mm) Continuous        |
|                      |                                               |
|                      | > Continuous milled rumble strips used on     |
|                      | > bituminous shoulders that are 1\' (300 mm)  |
|                      | > wide and located 4" (100 mm) from the       |
|                      | > painted edge-line (see Figures 1 and 2).    |
+----------------------+-----------------------------------------------+
| > Multi-lane and     | #####                                         |
| > two-lane highways  |                                               |
| > with 27= (8 m)     | ##### Type 4 - Modified Structural            |
| > wide concrete      |                                               |
| > pavement (new or   | > Structural rumble strips shall be modified  |
| > existing) in lieu  | > such that they are 3' (1 m) long and placed |
| > of Type 2.         | > on every other concrete panel. They shall   |
|                      | > be centered at the mid-point of the panel.  |
|                      | > The right edge of the painted edge-line     |
|                      | > shall be placed adjacent to the left        |
|                      | >                                             |
|                      | > edge of the rumble strip (see Figure 3).    |
+----------------------+-----------------------------------------------+

^1^ Type 4 rumble strips may be used on 27\' (8 m) wide concrete
pavement on freeways in lieu of Type 1A and Type

1B at the Designer's discretion.

Technical Memoradum No.: 00-08-DS-01

May 9, 2000

Page 3

##### Questions

Any questions regarding the content or implementation of this technical
memorandum should be referred to Amr Jabr, Design Standards Engineer
(651/296-4859).

Any questions regarding the publication or distribution of this
technical memorandum should be referred to Amr Jabr, Design Standards
Engineer (651/296-4859) or Susan Berndt, Office and Administrative
Specialist (651/296-9570).

Attachments:

Figure 1: Shoulder Rumble Strip - Section View (English)

Figure 2: Shoulder Rumble Strip - Plan View (English)

Figure 3: Modified Structural Rumble Strip (English)

Figure 4: Shoulder Rumble Strip - Appropriate Breaks (English)

Figure 1: Shoulder Rumble Strip - Section View (Metric)

Figure 2: Shoulder Rumble Strip - Plan View (Metric)

Figure 3: Modified Structural Rumble Strip (Metric)

Figure 4: Shoulder Rumble Strip - Appropriate Breaks (Metric)

**-END-**

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height="8.127777777777778in"}

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height="8.997222222222222in"}

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# Cited References

1\. Ligon, Claude, et al. *Effects of Shoulder Textured Treatments on
Safety*. Federal Highway Administration, FHWA/RD-85/027, 1985.

2\. Higgins, J. S. and W. Barbel. *Rumble Strip Noise.* [Transportation
Research Record]{.underline}. No. 983, 1984, 27-36.

3\. Cheng, Eric, et al. *Application and Evaluation of Rumble Strips on
Highways.* Utah Department of Transportation. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/resources/chengite.htm. August
2000.

4.  Wood, Neal E. *Shoulder Rumble Strips: A Method to Alert "Drifting
    Drivers.* Pennsylvania Turnpike Commission. January 1994. Online
    Posting.
    http://safety.fhwa.dot.gov/rumblestrips/resources/snap4pub.htm.
    August 2000.

5\. Khan, A. and A. Bacchus. *Economic Feasibility and Related Issues of
Highway Shoulder Rumble Strips*. [Transportation Research
Record]{.underline}. No. 1498, 1995, 92-101.

6\. Hickey Jr., John. *Shoulder Rumble Strips Effectiveness;
Drift-Off-Road Accident Reductions on the Pennsylvania Turnpike.*
[Transportation Research Record]{.underline}. No. 1573, 1997, 105-109.

7\. Perrillo, Kerry. *The Effectiveness and Use of Continuous Rumble
Strips.* August 1998. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/resources.rumblekp.htm. August
2000.

8\. Griffith, Michael. *Safety Evaluation of Continuous Shoulder Rumble
Strips Installed on Freeways.* [Transportation Research
Record]{.underline}. No. 1665, 1999, 28-34.

9\. Moeur, Richard. *Analysis of Gap Patterns in Longitudinal Rumble
Strips to Accommodate Bicycle Travel.* [Transportation Research
Record]{.underline}. No. 1705, 2000, 93-98.

10\. Elefteriadoiu, L. et al. *Bicycle Tolerable Shoulder Rumble
Strips*. Pennsylvania Department of Transportation, 2000.

11. Chen. A Study of Effectiveness of Various Shoulder Rumble Strips on
    Highway Safety. Virginia Department of Transportation, 1994.

12. California Department of Transportation. *Evaluation of Milled-In
    Rumble Strips, Rolled-In Rumble Strips and Proprietary
    Applications*. California State. Draft Report. February 2001.

13\. Outcalt, William. *Bicycle-Friendly Rumble Strips.* Report No.
CDOT-DTD-R-2001-4. Colorado Department of Transportation, 2001.

14\. Isackson, Cassandra. *Continuous Milled Shoulder Rumble Strips;
Nationwide Survey.* Minnesota Department of Transportation, February
2000.

15\. Federal Highway Administration, Wyoming Division Office. *Shoulder
Rumble Strips B Effectiveness and Current Practice.* April 1998. Online
Posting. http://safety.fhwa.dot.gov/rumblestrips/effectiveness/wy.htm.
July 2000.

16\. League for the Hard of Hearing. *Noise Levels in our Environment
Fact Sheet.* March 1999. Online Posting.
http://www.lhh.org/noise/decibel.htm. October 1999.

17\. Harwood, Douglas. *Use of Rumble Strips to Enhance Safety.*
National Cooperative Highway Research Program, Synthesis of Highway
Practice 191, 1993.

18\. American Association of State Highway and Transportation Officials.
*Guide for the Development of Bicycle Facilities*. Washington, D.C.
AASHTO, 1999.

19\. Gårder, Per. *Rumble Strips or Not Along Wide Shoulders Designated
for Bicycle Traffic?* [Transportation Research Record]{.underline}. No.
1502, 1995, 1-7.

20\. Arizona Department of Transportation. *Continuous Longitudinal
Rumble Strips.* [ADOT Traffic Engineering Policies, Guidelines, and
Procedures]{.underline}. Section 480. 2000.

21\. Pennsylvania Department of Transportation. *Milled Shoulder Rumble
Strips (MSRS); Safety Enhancement.* Memo from Michael Ryan, Deputy
Secretary to District Engineers. Dated April 21, 1995 with attachments.

22\. Wyoming Department of Transportation. *Shoulder Rumble Strips.*
[Operating Policy]{.underline}. No. 7-3. 1998.

23\. New Mexico State Highway and Transportation Department. *Rumble
Strip Guidelines*. 1992.

24\. Ohio Department of Transportation. *Rumble Strips.* [Roadside
Safety Devices]{.underline}. Section 605.

25\. Oklahoma Department of Transportation. *Rumble Strip Policy*. 2000.

26\. Minnesota Department of Transportation. *Rumble Strips on Shoulders
of Rural Truck Highways.* Minnesota Department of Transportation
Technical Memorandum. No. 00-08-DS-01. 2000.

27\. Washington Department of Transportation. *Rumble Strips.* [Revised
Code of Washington]{.underline}. Section 46.61.160.

28\. New York State Department of Transportation. *Safety shoulder
Rumbles Strips (Safe-Strips) Policy and Revised Installation Details.*
New York State. Engineering Instruction 97-013. 1997.

29\. Watts, G. R. *The Development of Rumble Areas as a Driver Alerting
Device."* Supplementary Report No. 291. [Transport and Road Research
Laboratory]{.underline}. (1977).

# BIBLIOGRAPHY

American Association of State Highway and Transportation Officials.
*Guide for the Development of Bicycle Facilities*. Washington, D.C.
AASHTO, 1999.

Arizona Department of Transportation. *Continuous Longitudinal Rumble
Strips.* [ADOT Traffic Engineering Policies, Guidelines, and
Procedures]{.underline}. Section 480. 2000.

ASCE Human Powered Transportation Committee. *Comments TEA-21, October
30, 1998*. Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/tea21.htm. August
2000.

ASCE Human Powered Transportation Committee. *Committee Meeting Minutes
January 13 and 15, 1997*. Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/min_0197.htm. August
2000.

ASCE Human Powered Transportation Committee. *Committee Meeting Minutes
January 12 and 14, 1998*. Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/min_0198.htm. August
2000.

ASCE Human Powered Transportation Committee. *Committee Meeting Minutes
January 10, 1999*. Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/min_0199.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. April 1999.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0499.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. August 1996.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0896.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. December 1997.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_1297.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. February 1997.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0297.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. February 2000.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0200.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. June 2000. Online
Posting: http://ourworld.compuserve.com/homepages/kbarrett/upd_0500.htm.
August 2000.

ASCE Human Powered Transportation Committee. *Update*. March 1998.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0398.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. September 1997.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0997.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. September 1998.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0998.htm. August
2000.

ASCE Human Powered Transportation Committee. *Update*. September 1999.
Online Posting:
http://ourworld.compuserve.com/homepages/kbarrett/upd_0999.htm. August
2000.

Bennett, R. Clarke. *FHWA Notice.* N 7560.9. April 1987. Online Posting.
http://www.bikeplan.com/rumble1.html. July 2000.

Bicycle Transportation Alliance. *Alert, Rumble Strips.* Online Posting.
http://www.telepoert.com/\~bta4bike/act/alert/a-rumble.htm. July 2000.

Bike Plan Source. *Comments on the AASHTO Guide for the Development of
New Bicycle Facilities.* Online Posting.
http://www.bikeplan.com/guidedes.htm. July 2000.

California Department of Transportation. *Rumble Strips.* [Caltrans
Traffic Manual]{.underline}. Section 6-03.2. 1999.

California Department of Transportation. *Evaluation of Milled-In Rumble
Strips, Rolled-In Rumble Strips and Proprietary Applications*.
California State. Draft Report. February 2001.

CH2MHILL. *Initial Draft of a Compendium of Strategies.* National
Cooperative Highway Research Program, Project 17-18(3), September 2000,
4-1 -- 4-10.

Cheng, Eric, et al. *Application and Evaluation of Rumble Strips on
Highways.* Utah Department of Transportation. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/resources/chengite.htm. August
2000.

Chung. *A Study of Effectiveness of Various Shoulder Rumble Strips on
Highway Safety*. Virginia Department of Transportation, 1994.

Dorman, Frank. *VDOT Installs High Tech 'Rumble Strips' on Smart Roads.*
November 1999. Online Posting.
http://www.vdot.state.va.us/info/News/state/1999/nrCO11231999_rumble.htm.
July 2000.

Elefteriadoiu, L. et al. *Bicycle Tolerable Shoulder Rumble Strips*.
Pennsylvania Department of Transportation, 2000.

Federal Highway Administration, Wyoming Division Office. *Shoulder
Rumble Strips B Effectiveness and Current Practice.* April 1998. Online
Posting. http://safety.fhwa.dot.gov/rumblestrips/effectiveness/wy.htm.
July 2000.

Federal Highway Administration. *Guidebook on Method to Estimate
Non-Motorized Travel.* Report No. FHWA-RD-98-166, Federal Highway
Administration, 1998.

Federal Highway Administration. *Rumble Strip; Survey Summary Results.*
Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/resources/hqsurvey.htm. August
2000.

Federal Highway Administration. *Rumble Strips are LOUD!*. Online
Posting:
http://safety.fhwa.dot.gov/fourthlevel/rumble/concern_noise.htm.
November 2000.

Federal Highway Administration. *Rumble Strips; Bicycles and Things That
Go Bump on the Road.* Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/issues/bikeissues.htm. July
2000.

Federal Highway Administration. *Rumble Strips; Discussion Group; Rumble
Strips and Bicycles.* October 1999. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/communication/threads.cfm. July
2000.

Federal Highway Administration. *Rumble Strips; Technical Questions
Received from Persons Communicating Via the Rumble Strip Web Site and
Responses Given by Jim Growney, FHWA Rumble Strip Expert.* February
1999. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/overview/maintenance2.htm. July
2000.

Federal Highway Administration. *Rumble Strips; The Four Types of Rumble
Strips.* Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/types.htm. July 2000.

[FHWA Transporter]{.underline}. July 2000, 5. Online Posting.
http://www.roads.detr.gov.uk/roadnetwork/tirm/tal/traffic/11_93/item1.htm.
July 2000.

Forkosh, Alan. *Rumble Strips B Act Now!* April 1999. Online Posting.
http://www.ebbc.org/hypermail/ebbc-talk/1999/htm. Discussion on East Bay
Bicycle Coalition Talk. July, 2000.

Gårder, Per. *Rumble Strips or Not Along Wide Shoulders Designated for
Bicycle Traffic?* [Transportation Research Record]{.underline}. No.
1502, 1995, 1-7.

Griffith, Michael. *Rolled-In Continuous Shoulder Rumble Strips Reduce
ROR Crashes.*

Griffith, Michael. *Safety Evaluation of Continuous Shoulder Rumble
Strips Installed on Freeways.* [Transportation Research
Record]{.underline}. No. 1665, 1999, 28-34.

Griffith, Michael. *Safety Evaluation of Roll-In Continuous Shoulder
Rumble Strips on Freeways.* [HSIS Report Summary Report]{.underline}
FHWA-RD-00-032, December 1999.

Harwood, Douglas. *Enhancing Highway Safety with Rumble Strips.* [TR
News]{.underline}. No. 178, May-June 1995, 12-16.

Harwood, Douglas. *Use of Rumble Strips to Enhance Safety.* National
Cooperative Highway Research Program, Synthesis of Highway Practice 191,
1993.

Hickey Jr., John. *Shoulder Rumble Strips Effectiveness; Drift-Off-Road
Accident Reductions on the Pennsylvania Turnpike.* [Transportation
Research Record]{.underline}. No. 1573, 1997, 105-109.

Higgins, J. S. and W. Barbel. *Rumble Strip Noise.* [Transportation
Research Record]{.underline}. No. 983, 1984, 27-36.

Isackson, Cassandra. *Continuous Milled Shoulder Rumble Strips;
Nationwide Survey.* Minnesota Department of Transportation, February
2000.

Khan, A. and A. Bacchus. *Economic Feasibility and Related Issues of
Highway Shoulder Rumble Strips*. [Transportation Research
Record]{.underline}. No. 1498, 1995, 92-101.

Khan, A. M. and A. Bacchus. *Bicycle Use on Highway Shoulders.*
[Transportation Research Record]{.underline}. No. 1502, 1995, 8-21.

Kugler, B. Andrew, et al. *Highway Noise; A Design for Prediction and
Control.* [National Cooperative Highway Research Program]{.underline}.
Transportation Research Board, Synthesis 174, 1976.

League for the Hard of Hearing. *Noise Levels in our Environment Fact
Sheet.* March 1999. Online Posting.
http://www.lhh.org/noise/decibel.htm. October 1999.

Ligon, Claude, et al. *Effects of Shoulder Textured Treatments on
Safety*. Federal Highway Administration, FHWA/RD-85/027, 1985.

Memphis City Schools. *Physics Tutorials; Sound; Decibel Levels* Online
Posting:
http://www.memphis-schools.k12.tn.us/admin/tlapages/sound_decibel.htm.
October 2000.

Minnesota Coalition of Bicyclists. *MCB Position Paper on 'Run-Off-Road'
Rumble Strips.* Online Posting.
http://www.winternet.com/\~rtandems/mcb/ror1.thml. July 2000.

Minnesota Department of Transportation. *Rumble Strips on Shoulders of
Rural Truck Highways.*

Minnesota Department of Transportation Technical Memorandum. No.
00-08-DS-01. 2000.

Moeur, Richard. *Analysis of Gap Patterns in Longitudinal Rumble Strips
to Accommodate Bicycle Travel.* [Transportation Research
Record]{.underline}. No. 1705, 2000, 93-98.

Moeur, Richard. *What I (and Others) Have to Say About Cycling.* October
1999. Online Posting. http://members.aol.com/rcmoeur/opinbike.html. July
2000.

Morgan, Rick and Dan McAuliffe. *Effectiveness of Shoulder Rumble
Strips: A Survey of Current Practice.* Report No. FHWA/NY/SR-97/127. New
York State Department of Transportation, 1997.

National Center for Bicycling and Walking. *Rumble Strips; Grumblings on
Rumble Strips: Perspectives from around the US.* Online Posting.
http://www.bikefed.org/rumble.htm. August 2000.

National Highway Traffic Safety Administration and National Center on
Sleep Disorders Research. *A Report to Congress on the Collaboration
Between the National Highway Traffic Safety Administration (NHTSA) and
the National Center on Sleep Disorders Research (NCSDR)*. 1999.

New Mexico State Highway and Transportation Department. *Rumble Strip
Guidelines*. 1992.

New York State Department of Transportation. *Safety shoulder Rumbles
Strips (Safe-Strips) Policy and Revised Installation Details.* New York
State. Engineering Instruction 97-013. 1997.

O'hanlon, James and Gene Kelley. *A Psychophysiological Evaluation of
Devices for Preventing Lane Drift and Run-Off-Road Accidents.* Technical
Report No. 1736-F. California Department of Transportation, 1974.

Ohio Department of Transportation. *Rumble Strips.* [Roadside Safety
Devices]{.underline}. Section 605.

Oklahoma Department of Transportation. *Rumble Strip Policy*. 2000.

Pennsylvania Department of Transportation. *Milled Shoulder Rumble
Strips (MSRS); Safety Enhancement.* Memo from Michael Ryan, Deputy
Secretary to District Engineers. Dated April

21, 1995 with attachments.

Perrillo, Kerry. *The Effectiveness and Use of Continuous Rumble
Strips.* August 1998. Online Posting.
http://safety.fhwa.dot.gov/rumblestrips/resources.rumblekp.htm. August
2000.

Schimek, Paul. *The Dilemmas of Bicycle Planning.* Presented at the
Association of Collegiate Schools of Planning. July 1996.

Snyder, Richard. *Bituminous Shoulder Rumble Strips.*" Research Project
90-059, Pennsylvania Department of Transportation. 1994.

Stonecypher, T. Lamar. *Rumble Strips; Victory.* June 2000. Online
Posting. http://www.gate.net/\~1stone/rumble.htm. July 2000.

Stutts, James. *Sleep Deprivation Countermeasures for Motorist Safety.*
[National Cooperative Highway Research Program]{.underline}.
Transportation Research Board, Synthesis 287, 2000.

The Noise Center. *Noise Levels in our Environment Fact Sheet.* March
1999. Online Posting: http://www.lhh.org/noise/decibel.htm. October
2000.

TranSafety Reporter. *Shoulder Rumble Strips Proven Effective on the
Pennsylvania Turnpike.*" [TranSafety Reporter]{.underline}. Vol. 16, No.
8, August 1998, 5-6.

Tye, E. J. *Devices to Prevent Run-Off-Road Accidents.* Report No.
CA-DOT-TR-1269\--76-01. California Department of Transportation, Office
of Traffic. 1976.

U.S. Roads. *Shoulder Rumble Strips Proven Effective on the PA
Turnpike.* [Road Injury Prevention and Litigation Journal]{.underline}.
August 1998.

United Kingdom, Department of the Environment, Transport and the
Regions. *Rumble Devices.* Traffic Advisory Leaflets -- Traffic
Management. June 1998. Online Posting.

Outcalt, William. *Bicycle-Friendly Rumble Strips.* Report No.
CDOT-DTD-R-2001-4. Colorado Department of Transportation, 2001.

Walls, Ann. *A Silver Bullet: Shoulder Texture Treatments.* [Public
Roads]{.underline}. Vol. 62, No. 4, January 1999, 9-12.

Washington Department of Transportation. *Rumble Strips.* [Revised Code
of Washington]{.underline}. Section 46.61.160.

Watts, G. R. *The Development of Rumble Areas as a Driver Alerting
Device."* Supplementary Report No. 291. [Transport and Road Research
Laboratory]{.underline}. (1977).

Williams, John. *Rumble Strips: A Growing Threat to America=s Cyclists?*
[Bicycle Forum]{.underline}. Vol. 14, April 1987.

Wisconsin Department of Transportation. *Cross-Section Elements for
Rural Highways and Freeways*. [Facilities Development
Manual]{.underline}. 2000.

Wood, Neal E. *Shoulder Rumble Strips: A Method to Alert "Drifting
Drivers.* Pennsylvania Turnpike Commission. January 1994. Online
Posting. http://safety.fhwa.dot.gov/rumblestrips/resources/snap4pub.htm.
August 2000.

Wyoming Department of Transportation. *Shoulder Rumble Strips.*
[Operating Policy]{.underline}. No. 7-3. 1998.