U.S. Department of Transportation
Federal Highway Administration
TECHNICAL ADVISORY
T 5040.35
December 20, 2001
Par.
What is the background on rumble strip development and use?
When is the use of rumble strips warranted?
What types of rumble strip designs are most often used?
(1) Milled-in: This design is made by cutting (or grinding) the pavement surface with carbide teeth affixed to a 600 mm (24 in) diameter rotating drum. The indentations formed are approximately 13 mm (1/2 in) deep, 180 mm (7 in) wide parallel to the travel lane and 400 mm (16 in) long perpendicular to the travel lane. The indentations are approximately 300 mm (12 in) on center and offset from the edge of the travel lane a distance of 100 mm (4 in) to 300 mm (12 in). Some research has been completed recently on the effectiveness of narrower and shallower cuts. Such variations from the original dimensions are discussed in detail in paragraph 8.
(2) Rolled-in: The rolled-in design is generally installed by using a steel wheel roller to which half sections of metal pipe or solid steel bars are welded. The compaction operation presses the shape of the pipe or bar into the hot asphalt shoulder surface. The resultant shape is generally 25 mm (1 in) deep, 50 mm (2 in) to 64 mm (2.5 in) wide parallel to the travel lane and 450 mm (18 in) to 900 mm (35 in) long perpendicular to the travel lane. The indentations are usually set 200 mm (8 in) on center and offset from the travel lane edge from 150 mm (6 in) to 300 mm (12 in).
(3) Formed: The formed rumble strip is added to a fresh concrete shoulder with a corrugated form which is pressed onto the surface just after the concrete placement and finishing operations. The resultant indentations are approximately 25 mm (1 in) deep, 50 mm (2 in) to 64 mm (2.5 in) wide parallel to the travel lane and 400 mm (16 in) to 900 mm (35 in) long perpendicular to the travel lane. The indentations may be in continuous pattern, but are generally in groups of five to seven depressions spaced approximately 15 m (50 ft) apart and offset from the travel lane at about 300 mm (12 in).
(4) Raised: Raised rumble strip designs can be made from a wide variety of products and installed using several methods. The elements may consist of raised pavement markers, a marking tape affixed to the pavement surface, an extruded pavement marking material with raised portions throughout its length or an asphalt material placed as raised bars on the shoulder surface. The height of the raised element may vary from 6 mm (1/4 in) to 13 mm (1/2 in). Spacing and width across the shoulder vary widely.
(1) Most states offset shoulder rumble strips just outside the edge line of the travel lane by a distance of 100 mm (4 in) to 300 mm (12 in). This keeps the strip elements some distance from the construction joint between the travel lane and shoulder; it helps reduce the number of inadvertent hits from passing traffic, especially larger trucks; and it allows for a substantial width of the paved shoulder to remain available for other users of the shoulder. A few states prefer to offset the rumble strip by as much as 770 mm (30 in) on wide shoulders to allow for maintenance vehicles and work zone traffic to straddle the rumble strip when driving on the shoulder. Such placement, however, moves the strip further away from the travel lane and narrows the recovery area outside the strip, thereby reducing the time available for an errant motorist to take corrective action after crossing the rumble strip. It also reduces the travel path available to bicyclists using the shoulder.
(2) Some states have installed milled-in shoulder rumble strip elements 300 mm (12 in) in width perpendicular to the travel lane instead of the original 400 mm (16 in). This is done to leave more of the paved shoulder clear for bicyclists. If the width is made much less than 300 mm (12 in), there is concern that a vehicle's tires, especially those of a large truck, may bridge the indentations, making them less effective in providing a vibration alert. However, at least one study found that large vehicle ROR crashes were a very small percentage of the overall problem. Some states have used rumble strips even narrower than 300 mm (12 inches) on facilities with particularly narrow shoulders and significant run-off-road crash experience. At least two states have installed 200 mm (8 in) strips coincident with the roadway edge lines.
(3) A few states place shoulder rumble strips along the freeway acceleration and deceleration lanes. However, most install the strip only along the shoulder near the edge of the through travel lanes and stop it at the beginning and end of auxiliary lanes. Shoulder rumble strips are generally not placed on freeway ramps, although they have been used to alert drivers of an especially tight turn entering the exit ramp.
(1) Most shoulder rumble strips are installed without any breaks or gaps except at exit and entrance ramps and at street intersections and major driveways on non-freeway facilities. The strips are not placed near the intersection or driveway approaches to allow vehicles to maneuver into and out of the intersections and driveways.
(2) At least one state uses an intermittent gap in their freeway rumble strip installation of 1.5 m (5 ft) in length between sets of milled-in elements 2.1 m (7 ft) in length. This state determined that this length of gap in the strip provides more of an alert sensation to the driver than does the continuous strip.
(3) In some of the first installations of formed-in rumble strip elements on concrete shoulders, the spacing between groups of corrugated elements was often between 12 m (40 ft) and 15 m (50 ft). While an errant driver might hit some of these elements on the shoulder, they were not as effective in alerting drivers as continuous shoulder rumble strips. Most strips on concrete are now placed continuously with the elements spaced 300 mm (12 in) on center and offset from transverse shoulder joints by at least 200 mm (8 in).
How are rumble strips typically installed?
How can the adverse effects of rumble strips on bicyclists be reduced?
"Rumble strips or raised pavement markers are not recommended where shoulders are used by bicyclists unless there is a minimum clear path of 0.3 m (1 ft) from the rumble strip to the traveled way, 1.2 m (4 ft) from the rumble strip to the outside edge of paved shoulder, or 1.5 m (5 ft) to adjacent guardrail, curb or other obstacle."
What are the FHWA's recommendations for the installation of shoulder rumble strips?
(1) Standard milled rumble strips, installed as close to the edge line
as practical, should be used when a 2.4 m (8-foot) clear shoulder width
remains available after installation of the rumble strip. This is the
recommended treatment for roadways with 3.0 m (10 foot) shoulders.
(2) A modified design should be used along shoulders 1.8 or 2.4 m (6 or 8 feet) wide when the remaining available clear shoulder width is less than 1.8 m (6-feet) and the road can be used by bicyclists. The most recent studies indicate a milled depth of approximately 10 mm (3/8 inch) provides reasonable warning to most motorists while not being unduly dangerous to cross on a bicycle when necessary. Several states have used narrower strips (e.g., 300 mm (12 inches) or less) perpendicular to the direction of traffic with apparent success. Others, as noted above, have adopted a gap spacing to allow a bicyclist to cross into the travel lane and back without having to ride directly over the rumble strips. Since rumble strips are not intended to be ridden on by bicyclists and should be crossed with care, gaps in the strip pattern may be more effective in allowing safe crossings and are much easier to achieve than modest reductions in the depth of each milled strip. A 3.6 m (12 ft) long gap between 14.6 (48 ft) long sections of rumble strip is recommended. Consideration should be given to increasing the gap spacing, narrowing the width of the rumble strips, widening the shoulders for bicycle use, or all of the above on long downhill grades where bicycle speeds are likely to increase significantly.
(3) Rumble strips should not normally be used when their installation would leave a clear shoulder pathway less than 1.2 m (4-feet) wide (or less than 1.5 m (5-feet) wide if there is an obstruction such as a curb or guardrail) to the right of the rumble strip for bicycle use. At locations where such space does not exist to the right of the rumble strip, a rumble strip may be installed if it is at least 0.3 m (1 foot) to the right of the edge line. In this case, a bicyclist would be expected to ride to the left of the rumble strip, essentially along the outside edge of the traffic lane.
Yes, the following references apply to the use of rumble strips.
/s/
Rudolph M. Umbs
Acting Director, Office of Safety Design