MEMORANDUM

TO: Distribution

FROM: David T. Bloom, P.E. t~

Preconstruction Engineer Northern Region

State of Alaska Department of Transportation & Public Facilities Northern Region Design & Engineering Services

DATE: October 15,2003

FILE NO: Dave/Rumble Strip Installation.doc TELEPHONE NO: 451-2274

FAX NO: 451-5126

SUBJECT: Policy for Rumble Strip Installation

Attached is a "refresher" copy ofthe current departmental policy, dated 5/30/01, for rumble strip installation. Please ensure our projects conform to this policy.

In reference to Item 1, Installation Method, regional practice has been to use rolled-in rumble strips on individual projects as an interim measure, with milled-in rumble strips to be done later on a more cost­effective, region-wide project.

However, rolled-in rumble strips have been found to be of questionable benefit. Therefore, effective today, rolled-in rumble strips will no longer be included in our PS&E's.

The intent is still to develop a region-wide project for milled-in rumble strips. To support that effort, Traffic & Safety will develop an inventory of existing milled installations.

Milled-in rumble strips should still be considered on individual projects, which have locations with a high run-off-the-road accident history.

The Design Study Report for each project should specifically address rumble strips, in Safety Improvements section.

GCT/lmc

Attachment: As stated

Distribution: Michael L. Downing, P.E., Chief Engineer, Headquarters (w/o attachment) Joseph H. Keeney, P.E., PD&E Chief, Northern Region (w/attachment) Longin Krol, P.E., Regional Construction Chief, Northern Region (w/o attachment) Patricia D. Miller, P.E., Design Group Chief, Northern Region, (w/attachment) Mark J. Neidhold, P.E., Traffic & Safety Chief, Northern Region, (w/attachment) Andrew J. Niemiec, P.E., Regional Director, Northern Region (w/o attachment) Howard Thies, M&O Director, Northern Region (w/o attachment) Gary C. Tyndall, P .E., Design Group Chief, Northern Region (w/attachment)

- ~EMO.RANDUM TO: DISTRIBUTION

. FROM: :Mi~ L Downing, P J!.ci!J Chief Engineer . . .

State of Alaska Department of Transportation and Public Facilities

Statewide Design and Englgeerlng Services Division

DATE: May30, 2001

FILENO:

TELEPHONE NO: 465-2950 FAX NUMBER: 465-2460

TEXt' TELEPHONE: 465-3652

SUBJECT: Rumble Strip Policy

The attachment defines ~partmental poli;cy for rw:ilble strip installation. It supmedes my April. ~3, 1999 memo on this topic. we: have le~ed more since then thiough Centtal Region's rumble stiip pr6j~ on;.going research oy the· department's Research· Section, 'arid from national research. Changes are intended to maintain safety benefits for automobiles, improve bicycle and wheelchair friendliness, and maintain pavement longevity.

We have not adopted some suggestions for mitigation of the negative impacts of rumble strips. This is either because they make rumble strips less effective as a safety enhancement or because there is not enough data to validate their effectiveness. We'don't want to mitigate away ramble strips' reason f~r being- to save lives by keeping dozing, distracted, or inattentive drivers on the ro~: . .

These are not comprehensive guidelines. Issues not covered here are left to regional discretion. Additional guidance will be provided as we get more experience. As our policy stabilizes, it will be in~orpora.ted in statewide standard drawings and/or the P:reconstruction Manual.

. .

, Rumble strips are the most cost-effective safety improvement we have identified. Thank you for 'yo~ efforts to install them where appropriate. .

Please ensure that rumble strips in your region confonn to the attached policy.

Attachment

DISTI®UTION: Steven Hom, P .E., Preconstmction Engineer, Central Region Pat Kemp, P .E., Preconstruction Engineer, Southeast Region Dave McCaleb, P .E., Preconstruction Engineer, Northern Region

cc: Dave Bloom, P .E., Preliminary Engineering Chief, Northern Region D&Es Tom Brigham, Director, Division pf Statewide Planning, HQ Don Brandon, ADA Coordinator, 'Vocational Rehabilitation, Department of Labor Judy Chapman, Planner III, Divisio~ of Statewide Planning, HQ

-2-

. . ...

. May 30, 2001

r.··' Duane Doerflinger, P .E., Preconstruction Standarpg Engineer, D&C Standards, HQ D&ES Robert Doll, P .E., Regional Director, Southeast Region

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David Eberle, P .E., Regional Director, Central Region AI Fletcher, P.E., Traffic/Safety Operations, Federal Highway Administration Gail Gardner, P .E., Regional Traffic Engineer, Northern Region D&ES Gary Hogins, P_.E., Chief, Design &. Construction Standards, HQ D&ES . Robert Laurie, Planner m, Division of Planning, HQ . . Michael Lukshin, P .E., Regional Traffic Engineer, Southeast Region D&.ES Kurt Smith, P .E., State Traffic Engineer, D&C Standards, HQ D&ES Ralph Swarthout, P .E., Regional Director, Northern Region Scott Thomas; P .E., Regional Traffic Engineer, Central Region D&ES Alex Viteri, P .E., ~sistant State Traffic Engineer, D& C Standards, HQ D&ES

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: ~Iaska DOTIPF Polley on Rumble Strip lnstall~tion ,.--.,_ 1~ 1. InStallation Method: Milled rumble strip~ are more effective safety enhancements than rolled-

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in rumble strips. They should be used wherever their installation is feasible. In other cases, rolled-in rumble strips II;Uly be used as an interim treatm.~nt

. 2. Lateral Width: 400 mm (16")

3. Longitudinal Milling Pattern: 175 mm (7") cut, 13 mm (lh") deep, 125 mm (5") flat )

4. Gaps for bicycles: Do not install gaps on roads where bicycles are prohibited. On other . roads use a 1.8 m (6') gap and a 10.2 m (34') rumble on a 12.0 m (40') cycle). The gap and rumble dimensions given are measured from center to center of grooves. The gap width from edge to C?dge of groove is 1.6 m <?' 5''). · ·

12.0 m (401 Cycle _ ...

"' 1.8m ~j Ctrto

1r 10.2 m (34') Centerto Center

_ ....

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~I , ... 1.6 m {5'5,

Edge to Edge

5. Offset between outside edge of shoulder stripe (and inside edge of nunble strip: • 1.8 m (6') Shoulders: 50 mm (2'') • Wider Shoulders: 150 mm (~'')

Note that if lane-lines or centerlines are used as control for rumble strip alignment, the above offsets should be measured from where the shoulder stripe should be, rather than where it is .

. 6. Alignment: Consider using the centerline or lane-lines, rather than the shoulder stripe, as

control for ~ble strip alignment This would require rnarldng a new ~e, independent of the shoulder stripe, as a guide for rumble strip alignment If this is done, Ie-stripe all locations where rumble strips overlap shoulder stripes or are inside of them. Existing striping

C·-:-.. should be removed at re-striped locations unless it has little effective life remaining. In.no

.~.) case should rumble strips be allow~d to protrude on the inside of final striping. 'l

5-30-01

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. / 7. Clear shoulder width outside of rumble st:dps:

• Segments with guardrail: Provide at least 5' (1.5 m) between the edge of rumble strip and the face of.rail (note that this precludes rumble strip installation on 1.8 m (6') shoulders with guardrail). .

• No guardrail: Provide at least 4' (1.2 m) between the edge of rumble an4 the edge of pavement.

• Segments where bicycles are prohibited: No minimum.

These width requirements apply to shoulders on climbing and passing lanes as well as other locations. '\ ·

A 150 mm (6") deviation from required clear widths is allowed for distances under 30 m (100'). If a width deficiency exceeds 150 mm or lasts longer than 30 m, the rumble strip shall be discontinued until the required clear width becomes available again.

Care in maintaining clear width: As-built plans are often inaccurate. Shoulder width should · be spot-chec~d during design and continuously checked durin~ cons~on•.

8. Speed Limit: Do not install rumbles where the speed limit is 45 MPH or lower.

9. Centerline rumbles: Do not install centerline rumble strips unless you have written approval from me. Do not install centerlin~ rumble strips, in any case, where it is legal to pass in either direction.

, 10. Lane-line delineating rumbles on multi-lane roads. Lane line rumble strips should not be l._ ,' wider than 150 mm (6'') or have more than a 3.3 m (10') total length in any skip stripe cycle.

11. Break rumbl~ strips for intersections, driveways and in front of multiple mailbox installations.

12. Do not install rumble strips on bridge decks, bridge approach slabs, or concrete weigh-in­motion slabs.

. . 13. Do not place rumble strips iri freeway exit gores. Terminate rumble strips 23 m (75') before

· exit ramp angle points.

14. Do not install rumbles on stripes separatiilg through lanes from turning lanes.

15. Do not install rumbles on pavement with substantial alligator and/or fatigue cracking.

16. Do not install rumbles on shoulders that are to be overlaid or reconstructed in the near future. I '

17. Do· not install rumbles on any pavement less than 51 m.m (2") thick

• During construction. width can be checked by fixing a 1.2 m ( 4 ') wide pointer bar (with an additional pointer at 1.05 m (3.5')) on the rumble strip milling machine.

. 5-30-01

·.y Rumble Strip Policy

Background /

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. Th~ following discussion explains some of the decisions that went into the DOT &PF rumble strip policy.

Rumble Time- a Primary Consideration. J

One important, but often overlooked, issue is· the length of time errant drivers typically spend on rumble strips. Motorists who test-drive rumble strips, usually by driving on them for several seconds, often don't understand why the rumbles need to be so loud and aggressive. 'What they're missing is how brief rumble time is for drivers who are at risk of leaving the road- around 6/10 of a second of outside-tire rumble for drivers leavmg at a 3 degree angle (less than 2Jl0 of a second if you only count the time the tire is in full­width contact with the rumble). Departures at greater angles result in even less rumble time. It takes a lot of noise and vibration to wake drivers in such a short time. For this reason, we need tO be conse~ative with any modifications that reduce noise, Vibration, or rumble time. ·. ·

Milling Pattern

We have chosen the common 7" Wide, ~" deep cut pattern over the newer 5" cut pattems recommended by Pennsylvania DOT in their ''Bicycle-Tolerable Shoulder Rumble Strips", 2000, for the following .reasons:

1. 5" cut rumble strips are substantially quieter than 7" cut rumble strips. 2. 5" cut ~ble strips are quieter yet for large-tired vehicles such as trucks and buses. 3. 5" cuts are slower to install and are consequently more e'j:pensive. According to

· Surface Preparation Technologies, the company that did the Central Region rumble strips last year, 5'' /3/8" cuts take more than four times as long to install as the 7" I ~" cut installed in Central Region. This is because they have to slow much more for each 5" cut than they do for the more gradual 7" cut

. 4. Smface imperfections result in llarge depth variance in the 5" /3/8"' cuts (machine tolerance is a greater proportion of total cut depth). . ·

5. There is little, or no, actual accident data on the effectiveness of 5" cuts. Pennsylvania has not installed any of these on their ~oads as of May 2001.

6. Although a 5" I~" cut was li~t as one of the options in the PennDOT study (and was selected as the DOT &PF stalld.ard in the first draft of this policy), it is not possible .to cut rumbles to those dimensions given the dimensions of the milling machine used (The 16"' .mill can't cut that deep with a 5" width).

Until additional testing and post-project crash analysis identifies pa~ms that are bicycle­friendly, effective, and economical, the department should stay with tbe·J;>attem used in Central Region last year. This is the Sonic Nap Alert Pattern (SNAP) developed by the Pennsylvania Turnpike Authority in the mid 1990s. It is the pattern that most states with milled rumble strips use, according to the FHW A Rumble Strip Web Site, and the pattern

. that the outstanding safety record o_f milled rumble strips resulted from.

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Sonic Nap Alert Pattern \...

Rumble Strip Lateral Width.

The most common width of milled rumble strips in the U.S. is 16". This width has contributed to.the outstanding crash-reduction record of rumble strips. We have been asked to change the standard width to 12" in Alaska.

Going to a 12" width would allow tis to provide more clear shqulder space for bicycles and/or ·greater offset from the shoulder stripe. On the ·ather hand, it ·would recluCe rumble time and, as a consequence, rumble strip effectiveness. ·

1. Effectiveness.

Sixteen inch rumbles soun'd significantly more substantial than twelve inch rumbles when crossed at an angle -more than you would expect from a 33% increase in width. To a large degree, this is due to the increased time tires are in full-width contact with the rumble. ·

Psrtlsl71re-Width Rumble Contact Full 71re-Width Rumble Conflict

Full tire-width rumble contact allows the tire to fully drop into the nimbles. ·It is the loudest interval of a rumble strip crossing and is most effective at getting drivers' attention. Its duration doubles when rumble width increases from 12" to 16" (assuming an 8" tire contact patch).

, . Wider rumble strips also improve safety on intermittent rumble strips. Additional width reduces the probability of a car's outer tires driving through a gap without contacting the rumble. ·

/2. Clear shoulder space. /

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The 12" width would give an additional4" that could be used to widen the clear shoulder . space. However, according to Central Region pe~onnel, this rarely would have made the difference between having adequate and inadequate shoulder width on their rumble strip project On roads with 8' or 10' shoulders, it never would have made that difference.

3. Offset

The additiona14" could also be used to increase the offset between the shoulder stripe and the rumble from 4" to 8". This would reduce inadvertent contact with rumble strips but would also limit the debris-free area available for bicyclists on the outside of the rumble. There is little agreement on how much of a benefit, or disadvantage, an increased offset would be.

In summary, going to 12" from 16'' would trade an important safety advantage, half of the full-contact rumble time, for a less important consideration- 4" more space for shoulder or o~set · ·

We should retain the 16" width that has proven effective throughout the nation. '

Offset from Shoulder: Sttipe.

The Central Region shoulder ruplble strips were installed at 4" from the edge of the shoulder st;ripe. Cwrent recommendations by DOT &PF personnel range from 2" to 10".

Considerations: 1) Larger offsets would reduce the frequency of accidental rumble strip contact 2) Larger offsets postpone the time when a dozing driver contacts the rumble, thus

limiting the time and area available for recovery. 3) Larger offsets limit the clear width available for bicyclists. 4) Larger offsets move bicyclists further into the debris on the shoulder. Wind blast

from cars keeps the inner part of the shoulder clear. This may result in bicyclists riding on the road side of the rumble strip. ·

5) Smaller offsets may improve striping longevity (due to drivers shying away from the rumbles) -· -

6) Offsets larger than 6" would .Preclude the use of 16" rumbles on 6' shoulders. A 6" offset with a 16" IWD.ble woiild allow rio margin of error for varying pavement wi4ths or stripe alignment

To maintain room for larger rumbles and some margin of ClTOf for clear width for bicycles, the inner edge of rumble strips should be offset 2" from the outer edge of the shoulder stripe on 6' shouldCI$. On wider shoulders, which have niore than the required clear width for bicyclists, an offset of 6" would reduce inadvertent IUillbie contact to some extent.

·y Gaps.

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The ideal rUm.ble strip gap pattern would allow aU bicyclists at all speeds to cross without · rumble contact but ensure that all departing automobiles at all departure angles would contact the rumbles for long enough to wake them. In practice, this is unattainable. The long, frequent gaps desired by bicyclists would result in some automobiles either missing the rumbles entirely or having too little rumble time to wake them.

Every gap pattern is a compromise between bicycle-friendliness and vehicle safety. Because we have to act with limited information (there is little data on the effectiveness of intennittent rumble strips), we should err on the side of vehicle safety.

The following facts are pertinent: 1. Florida is reportedly using a 7' rumble, 5' (4'5'' edge to edge) gap pattern. 2. ArccentAri.zonastudyrecomm.ends either a28'. or a48' rumble with a 12' gap. 3. The 12' gap recommended by the Arizona study was based.on 100% of riders of

varying abilities ·on different types of bikes being able to cross the gap without slowing from 25 MPH without touching a rumble on either side.

4. As shown. on the rotighly-to-:scale drawings on the following page, gaps can significantly reduce the effectiveness of rumble strips, either by allowing drivers to miss theni, or by reducing the duration and volume of rumble noise and vibration.

5. It is not difficult to drive off the road at an angle that would allow a car's outside tires to drive through a 12' gap without significant rumble contact. It is difficult tO attain the angle necessary to clear a 5' 5" gap. However, it is not difficult to attain the angle necessary to cross either wit;h no full-tire-width rumble contact

6. In addition to gap length, gap frequency plays an important part in the likelihood that rumble time will be reduced. Less frequent gaps reduce the probability that errant drivers will encounter them.

This information leads to no exact answer. However, because short gaps have the least negative impact on safety and still provide a significant benefit to bicyclists, they arc the best choice .

. A one foot in~ase oyer the 4'5" gap used in Florida (and installed on Hiland Road) wotild make bicycle crossing a little easier. It would result in 14% gaps in the rumble strip, which reduces the probability of encountering them, and would require motorists to depart at an unusually high angle to entirely miss the rumbles. It requires high-speed bicyclists to either slow or clip a .few rumbles as they cross the gap.

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The 40' cycle recommended by the Arizona study provides crossing opportunities every 1.8 seconds fQr bicyclists traveling at their average speed of 15 MPH.

Consequently, go with 6' c~to center (5'5~ edge to edge) gaps cvery40'. ··-

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6' Nominal Gap · (5'5" actual groove to groove)

(Alaska Policy) .

12' Gap (from Arizona Study)

ihe OUts/ departtn de Wheels Of

( can m£sl ththe road at 9~ Vehicle % ih e ltlmble entl-.dJegrees .

e outside •o::r Y. deParting th Wheels of a can mJs e IDad at VehiCle COntact s f~/1 tire-width3.2 degrees

entirely. rumble

5' Nominal Gap (4'5• ~ctual groove to gro~ye) (Fionda and Kansas Polley)

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