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New York Effectiveness Report

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Effectiveness of Shoulder Rumble Strips A Survey of Current Practice

Rick L. Morgan, Civil Engineer I
Dan E. McAuliffe, Civil Engineer I

Special Report 127, September 1997

Abstract

The New York State Department of Transportation recently adopted a policy and specifications for use of rumble strips or "audible roadway delineators" on shoulders to assist in preventing drift-off accidents. To verify the quality of this policy and specifications, transportation agencies in the United States and Canada were surveyed concerning current practice, and this report summarizes the responses. Rolled-in and milled-in delineators are used extensively in both countries, and both have advantages and disadvantages but are effective in preventing these accidents. Factors that must be considered when specifying these delineators include location, noise, safety of cyclists, shoulder condition and dimensions, and history or potential for drift-off accidents.

I. Introduction

New York State has just adopted a policy and specifications for installation of audible roadway delineators (ARDs), as published in Engineering Instruction EI 97-013, titled "Safety Shoulder Rumble Strips (Safe Strips) Policy and Installation Details," dated June 6, 1997 and appended to this report. At the request of the Department's Design Division and the former Traffic Engineering and Safety Division, additional information has been collected by surveying other transportation agencies in the United States and Canada concerning their standards and practices to assure the comprehensiveness of New York's new standards.

This study's objectives were 1) to solicit information on policies and standards of as many agencies as might respond, 2) to summarize the information collected, and 3) to recommend changes as needed for the Department's policy and specifications.

The focus was on rolled-in and milled-in ARDs (or "RIARDs" and "MIARDs") as used on shoulders to prevent "drift-off" accidents, although information was also requested on other ARD types and uses. The survey questions may be summarized as follows:

1. Have you an ARD placement policy (if so, please send a copy).
2. Have you standard specifications for ARDs (if so, please send a copy).
3. Have you used rolled-in or milled-in rumble strips? If so, how effective have they been? Have you had any problems during installation? If so, describe them. Have they required any maintenance to date? If so, what was wrong and how was it corrected?
4. Have other ARD types been used? If so, please describe them.
5. Have you published any reports on ARDs? If so, please send copies.
6. What has community reaction been to installation of ARDs? Have you had noise complaints?
7. Have ARDs been installed on roads where bicycles are allowed? If so, how were ARD installation details changed to accommodate bicycle traffic?

II. Results and Discussion

A. Survey of Other Transportation Agencies

Survey forms were sent to 57 transportation agencies in the United States and Canada, of which 34 responded. Seven (Maryland, New Brunswick, Saskatchewan, Vermont, the Chesapeake Bay Bridge and Tunnel District, the New York State Bridge Authority, and the Orlando Expressway Authority) said they had no experience in using or testing ARDs, although Orlando sent Florida's state specifications. Six (Connecticut, New Hampshire, Manitoba, Ontario, Oregon, and Quebec) have experimented with either RIARDs or MIARDs, but do not use them regularly or have no specifications for their use. Eighteen of the other 21 agencies stated that they use either RIARDs or MIARDs or both on shoulders. Thus, including the Florida specifications, information was obtained from 19 agencies:

1. For MIARDs only: Maine, Massachusetts, New Jersey, the New York State Thruway Authority, and Pennsylvania.
2. For RIARDs only: California, Idaho, North Carolina, South Carolina, Utah, West Virginia, and Wisconsin.
3. For both MIARDs and RIARDs: Colorado, Florida, Mississippi, Nebraska, Oklahoma, Texas, and Wyoming.

Three that use one type but not both said they have experimented with the other but do not use it currently. Thus, a total of nine have experimented with one or the other type on shoulders. Besides the three who use other ARD types or use RIARDs or MIARDs elsewhere than the shoulder (Alabama, New Mexico, and Rhode Island), 10 of the 19 that do use them on shoulder said they also have experience with other ARD types, or use RIARDs or MIARDs in the travel lanes as warning devices either approaching intersections having traffic-control devices, or approaching construction zones, or before tollbooths. Thus, a total of 13 agencies have had experience with other types or uses of ARDs.

B. Rolled-In Delineators (RIARDs)

Fourteen agencies responded that they use these on shoulders, and nine sent details of policy and specifications. Size, spacing, and location off the pavement edge vary. Length specified varies from 300 mm to full-shoulder width, with the majority in the range of 600 to 1000 mm. Widths vary from 38 to 100 mm, with three agencies specifying 38 mm, three others 50 to 63 mm, and another three 100 mm. Depth varies from 13 to 25 mm, with the majority specifying 19 mm.

Specified spacing varies least, ranging from 200 to 300 mm, with a majority toward the lower figure. Location off the pavement edge varies from 0 mm (full-shoulder width) to 750 mm, with 300 mm the most common offset distance (five agencies).

The three most frequently cited installation problems of concerns with this ARD type are 1) ACC temperature is critical during rolling -- if the mat is too hot the ACC tears or ravels, and if too cold proper ARD depth and shape cannot be obtained, 2) ACC must be properly compacted between delineators, and 3) roller operators find it difficult to maintain a straight line (two agencies report that they require fitting the roller with a special sighting device to assist the operator in maintaining a straight line).

Other installation problems or concerns include 1) aggregate being cruised by ribs on the roller, 2) shoving of ACC during rolling (corrected by requiring a special mix when RIARDs are specified), and 3) pipes welded to the roller to form the RIARDs flattening with use (solved by filling these pipes with metal rods). One agency requires a special roller with a third drum and a hydraulic ram to adjust the pressure applied to the ACC, so as to obtain proper shape and depth. They say that applied pressure is a function of ACC temperature and thickness, and obtaining that pressure is a trial-and-error process. (They sent a rough schematic of this roller).

C. Milled-In Delineators (MIARDs)

Twelve agencies say that they use this ARD type, with nine sending information on policy and specifications. MIARD size and spacing are less variable than for RIARDs. Six of the nine use MIARDs that are 400 mm long by 175 mm wide by 13 mm deep. The other three use the same depth but lengths of 600, 700mm, or across the full shoulder, and widths of 100 to 175 mm. All agencies specify 300-mm spacing center-to-center, and one of these also allows 1500 mm center-to-center. Offset from the pavement edge varies from 100 to 450 mm, with four agencies using a 100-mm offset, two a 450-mm offset, and the other three some distance between these extremes. The major complaint about this ARD type is its higher cost than RIARDs. Several agencies not using MIARDs cite cost as the reason. Only one notes any installation problems, experiencing some ACC breakup between grooves.

D. Other Delineator Types and Uses

Thirteen agencies use other types, or use RIARDs and MIARDs elsewhere than shoulders. Among these others are 1) raised ACC strips (either cold- or hot-mixed), 2) roughened shoulders, 3) surface mounted features (buttons, strips or markers), 4) thermoplastic rumble strips, or 5) a surface treatment (AC tack coat, with larger-than-usual aggregate).

Six agencies use ARDs in-lane to warn drivers of intersections ahead containing some form of traffic-control device, of work zones, or of tollbooths. Five of these six use either RIARDs or MIARDs as in-lane warning devices. The sixth uses polyurethane raised strips developed by the Strategic Highway Research Program (SHRP) as a temporary system when approaching work zones.

Some concerns noted include 1) in-lane ARDs presenting hazards to both bicyclists and motorcyclists, 2) noise startling drivers as they cross in-lane ARDs, 3) motorists maneuvering unpredictably to avoid in-lane ARDs, and 4) raised and surface-mounted ARDs being easily removed by snowplows.

Generally, agencies using in-lane RIARDs or MIARDs specify the same dimensions and spacings as on the shoulders.

E. Policies for Use of Shoulder Delineators

Fifteen agencies sent copies of their policies for use of shoulder delineators. Their general consensus is that these should be used on all rural interstates and other rural highways, especially where histories exist of frequent drift-off accidents. Continuous ARDs are considered more effective than cluster-type ARDs -- groups of 15 to 20 grooves spaced 15 to 20 m apart -- in preventing these accidents. Most agencies require them on both outside and inside shoulders of multi-lane divided highways, specifying minimum shoulder widths where they can be placed -- generally 2.7 m for outside shoulders and 1.3 m for inside. Some also state minimum speeds on highways where they should be used.

F. Concerns Regarding Cyclists

Four agencies do not use shoulder ARDs on routes where bicycles are permitted. Thirteen have included consideration of bicyclists into their specifications or policies concerning their use, regardless of whether they had actually used ARDs on routes where bicycles are permitted. Generally, policies entail one or more of the following: 1) allowing ARD placement only on shoulders wide enough still to provide ample room for cyclists to ride safely (one agency had a bicycling club prevent installation of shoulder ARDs beside a highway; these now are specified only beside a road having a shoulder with at least 1.8 m between the ARD end and outside shoulder edge), 2) placing the ARD as close to the pavement edge as specifications allow, to provide necessary space for cycling, or 3) shortening ARD length to provide necessary space.

G. Complaints and Problems

Only four agencies using shoulder ARDs mentioned complaints concerning excessive noise, but most respondents either recommend or specify their use only on remote, rural highways. A few have experienced some maintenance problems for shoulder rumble strips: 1) keeping them clear of debris and water, 2) development of longitudinal cracking along the ARD end closes to the pavement edge where the offset was only 150 mm (solved by increasing the offset to 300 mm), 3) minor ACC breakup between rumble strips, and 4) tendency for traffic eventually to flatten RIARDs thus diminishing their effectiveness.

III. Conclusions and Recommendations

This study's objective was to document policy concerning use and specifications for shoulder audible roadway delineators, and the responses permit the following observations:

1. Shoulder ARDs to help prevent drift-off accidents are being used or tested by numerous transportation agencies in the United States and Canada.
2. Although both RIARDs and MIARDs appear to be effective in preventing these accidents, some agencies have found MIARDs superior from the standpoints of ease and consistency of installation, durability, and crash reduction, especially for large trucks and buses.
3. Continuous-shoulder ARDs are preferred to cluster-type ARDs.
4. Noise complaints from both drivers and nearby residents must be considered when specifying ARDs.
5. Bicyclists must be considered with reference to size, location, and use of shoulder ARDs.
6. MIARDs are more expensive but easier to install that RIARDs.
7. In-lane ARDs are useful in warning drivers that they are approaching intersections having traffic-control devices, work zones, and tollbooths.
8. Several factors must be considered before specifying use of in-lane ARDs, including hazards they present to all types of cyclists, noise, and the safety problem caused by drivers maneuvering unpredictably to avoid them.

Based on these observations, the following recommendations are proposed:

1. Shoulder ARDs should be used on all rural highways with fully controlled access (interstates and parkways), as well as other high-speed rural multi-lane roads having only partially controlled access. They should be considered for any highway section having a history of drift-off accidents.
2. Use of shoulder ARDs in urban or dense residential areas should be restricted to shoulders already having a high frequency of drift-off accidents.
3. New York's current specifications for size, offset, and spacing of shoulder ARDs are appropriate.
4. New York's current policy for use of shoulder ARDs on highways permitting cyclists is appropriate.
5. Performance of shoulder ARDs to help prevent drift-off accidents should be monitored to see if current policy or specifications can be improved. Maintenance histories and problems should also be recorded for both types of shoulder ARDs to help determine which type is more effective: RIARDs with their difficulties during installation or MIARDs with their higher initial costs.

Acknowledgements

This study was conducted under administrative direction of Dr. Robert J. Perry, Director of Transportation Research and Development, and technical supervision of Dr. Wei-Shih Yang, Engineering Research Specialist II. The authors thank the many transportation agencies in the United States and Canada who responded to this survey, and for contributions of information concerning New York State practices, John E. Watson of the Safety Program Management Bureau, and Lyman-Terry L. Hale of the Design Quality Assurance Bureau.