Rumble Strips: Problems and Policies

The Advocacy Advance Team has produced a report on rumble strip policies and we are working with a number of states to ensure road agencies are enacting bicycle-tolerable rumble strip policies and adhering to them. However, we haven’t excerpted the report on the blog yet. So let’s start the week off with that.

You can read the whole report here (PDF). The League, the Alliance for Bicycling and Walking, and Adventure Cycling, held a conference call for advocates, see the notes from the call here (PDF). We also surveyed our club members to see how rumble strips are affecting them and what actions they’ve taken so far, here’s  a summary of the results (PDF).

Route 45, Southern Illinois (Photo provided by Ginny Sullivan of the Adventure Cycling Association)

BICYCLING AND RUMBLE STRIPS

Problems for Cyclists

What are rumble strips?: Rumble strips are raised or grooved patterns in a road’s shoulder designed to alert drivers with noise and vibrations that they are drifting off the roadway. They can be an effective safety measure to prevent run‐off‐the‐road (ROR) crashes, especially on limited‐access highways and rural two‐lane highways with long straight sections. (Rumble strips placed on the centerline can help prevent head‐on crashes.)

How do rumble strips impact cyclists?: Rumble strips are virtually impossible to ride a bicycle on or over– they are at best uncomfortable, even for a very short distance, and at worst can cause a cyclist to lose control of their bike and fall. They can damage a bicycle wheel, can cause a flat tire, and/or shake lose parts off a bicycle. Consequently, cyclists will avoid riding over themii – and when rumble strips leave no room on a shoulder, the cyclist will have no other option than to ride in the travel lane. While rumble strips do not deter car, truck or bus travel, they have a severe impact on bicycling travel, and have ruined popular cycling routes.

The negative impact of rumble strips on the ride‐ability of a roadway has prompted American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA) to provide guidance to follow when considering rumble strips on roadways used by cyclists. They recommend that rumble strips should not be used indiscriminately on roadways that are not limited‐access. Rumble strips should be used where there is a history of run‐off‐the‐road crashes; especially where there is sufficient recovery room for a motorist to react to the alert provided by the rumble strip; and when the impact cyclists can be minimized. This means that at least four feet of unobstructed roadway shoulder remains after the rumble strips have been installed.

States should train and monitor contractors to ensure best practices are followed. Advocates should work with their state DOTs, Municipal Planning Organizations (MPOs), and county road commissions to verify that unnecessary rumble strips are not installed and that preferred bicycling routes, especially, are kept free of rumble strips. It is important to get it right the first time. Improperly installed rumble strips are expensive to repair – often costing many times more than the original installation – and usually cannot be repaired without leaving behind an uneven surface or a shoulder prone to early failure.

Specific Elements to Address

1. Too wide – many rumble strips are excessively wide, removing limited space on the shoulder for bicyclists to travel.

2. Too deep – most rumble strips are ground‐in to depths that are excessive and dramatically more dangerous for cyclists.

3. Continuous – rumble strips without gaps in the strip do not allow a safe way for cyclists to cross, merge or turn without hitting rumble strips.

4. Placement – the lateral placement in a shoulder can make a shoulder that was once verycomfortable to a bicyclist unusable.

Rumble strips along GA 193 south-southwest of Chattanooga, Tennessee – near intersection with Battlefield Parkway (GA 2). Photo by Dennis Coello

Existing National Guidance

Many states develop their own rumple strip policies. National organizations and agencies such as the AASHTO and the FHWA have issued guidance on how state agencies can balance the motorist safety benefits of rumble strips with the needs of bicyclists. The following includes guidance to install rumble strips in ways that can minimize the harmful impact on bicycling. Ideally, rumble strips would rarely be used on roads where bicycling is expected. Rumble strips should be used only when careful study determines that they are needed to reduce risk in high ROR crash locations and when there is adequate space on the shoulder for drivers to recover. The following guidance should be considered the minimum standard.

AASHTO’s Guide for Development of Bicycle Facilities says that rumble strips “are not recommended where shoulders are used by bicyclists unless there is a minimum clear path of 0.3 m (1 foot) from the rumble strip to the traveled way, 1.2 m (4 feet) from the rumble strip to the outside edge of paved shoulder, or 1.5 m (5 feet) to adjacent guardrail, curb or other obstacle. If existing conditions preclude achieving the minimum desirable clearance, the width of the rumble strip may be decreased or other appropriate alternative solutions should be considered.” Cyclists find that placing the rumble strip 1 foot to the right of the edge line is unsatisfactory and strongly recommend a minimum of four or five feet on the outside of the shoulder.

The FHWA guidance on Roadway Shoulder Rumble Strips supports this policy, saying, “Rumble strips should only be installed when an adequate unobstructed width of paved surface remains available for bicycle use.” The guidance notes that 12 feet gaps placed periodically in the strips allow cyclists to avoid debris and parked vehicles on the shoulder, or safely pass over the rumble strip for any reason. Because rumble strips occupy the favored part of the shoulder closest to the roadway, which generally remains clearer of debris due to the draft caused by passing automobiles, the FHWA guidance recommends that highway maintenance agencies regularly sweep the entire shoulder along bike routes and high bike traffic areas. The guidance states that shallower (“reduced depth”) rumble strips, which are less jarring to cyclists, are a good compromise to accommodate bicyclists.

For rural freeways and expressways on the National Highway System, the FHWA guidance endorses “system‐wide installation” of rumble strips to take advantage of economies of scale. Since bicyclists are generally prohibited from these highways, and there is often a wide shoulder when they are allowed, this guidance is appropriate. For non‐freeway roads, such as rural multi‐lane and two‐lane roads, rumble strips should only be used if an engineering study or crash analysis shows that rumble strips would effectively reduce ROR crashes. If an engineering study recommends rumble strips, they should follow these guidelines:

1. Rumble strips can be used when eight feet remain clear on the shoulder (recommended for 10‐foot shoulders). They should be installed as close to the edge line as practical.

2. Along shoulders of 6 or 8 feet, the FHWA calls for shallower depths, narrower strips, and gaps in the strip to allow cyclists to cross, merge, turn, avoid debris, or pass other cyclists and parker cars. The guidance adds: “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 be used when they would leave less than 4 feet to the edge of the pavement or five feet if a curb or guardrail is present on the shoulder.

Given the safety benefits of rumble strips for drivers, their use is appropriate under the right conditions.

However, transportation agencies should – at a minimum – follow the guidance of AASHTO and FHWA.

Rumble strips should not be installed on popular bicycle routes, or anywhere with insufficient shoulder width. If a rigorous crash analysis or engineering study finds rumble strips appropriate, their installation should follow the guidance above.

See Adventure Cycling’s complete matrix of state policies, including trouble spots and role‐models

Best Practices

Not installing rumble strips on designated bicycle routes and other roads where bicycling is expected. For non‐freeway rural roads, strips should be installed only after proper study confirms a documented need.

Providing minimum shoulder width – 4‐foot shoulder, or 5 feet with guardrail are the bare minimum. Better examples include Alaska and Colorado that require a minimum 6 ft shoulder.

Adjusting placement of the rumble strips by placing strips close to edge line to increase available shoulder area, or on low speed roads by placing stripe away from edge line to allow cyclists to ride on the left side of the strip. Placing rumble strips on the edge line (a rumble stripe) both increases visibility of the white line and maximizes available shoulder area.

Providing gaps in regular intervals to give cyclists a chance to avoid debris along the shoulder, merge, turn, or pass other cyclists, some states include periodic gaps in the strips – at least 12 feet, every 40 or 60 feet of rumble strip.

Adjusting rumble strips dimensions – Pennsylvania, California, and Colorado have studied bicycle-tolerable rumble strip designs. The studies come to similar conclusions about the dimensions for such rumble strips.

• Width: 5 inches (127 mm)
• Depth: 0.375 inches (10 mm), and
• Spacing: 11 or 12 inches (280 or 305 mm)

When bicyclists need more of the shoulder or rumble strips are needed along a narrow shoulder, Torbic et al. report that narrower strips can “still generate the desired sound level differences in the passenger compartment.”

Conclusion

While there are safety benefits to rumble strips for drivers of motor vehicles, there are considerable drawbacks for cyclists, who are vulnerable next to high‐speed traffic. In accordance with FHWA guidance, rumble strips should be used on roads where bicyclists are prohibited or not expected. On routes used by bicyclists, rumble strips should not be installed indiscriminately; a careful traffic safety study should be conducted to demonstrate a clear problem and a projected impact on safety.

In the event that rumble strips are appropriate, states should follow bicycle‐tolerable practices that provide maximum clear shoulder space for cyclists. Using an implementation checklist based on the above rumble strip practices, state agencies and local road authorities should closely monitor contractors to ensure that the policy is being followed. Finally, agencies should follow the FHWA guidance, which recommends that agencies work closely with bicycling organizations to make sure they “address the safety and operational needs of all roadway users.”

Read whole Rumble Strip report.