Engineering ConcernsThe following is an e-mail discussion of several State and Federal highway engineers from around the US addressing concerns about possible adverse effects on asphalt shoulder pavement quality, snow plowing operations and large truck/trailer operations on rural freeways due to the presence of shoulder rumble strips.
From: Jim Growney
Dear Shoulder Rumble Strip Contact,
I am writing to you because you have let me know of your interest in this subject or your name is included on the contact list in the FHWA's rumble strip Internet website. This is intended to share the following information with you and seek your reaction if you wish to provide it.
Today I received the following message from Larry Christianson of the Oregon DOT regarding a number of concerns one of their maintenance districts expressed with shoulder rumble strips recently installed in their area.
I have a serious problem that I need help with. Here is the e-mail I got from our friends in the mountains of NE Oregon. Please let me know if this has been a problem with other states or how I can “mend fences” in this case. Thanks.
Feedback from Meacham Maintenance Section:
We are finding that these Rumble Strips are deteriorating under winter maintenance activities. We have numerous areas where the strips are breaking out and wearing down. They tend to fill with water and then freeze, becoming a trench of ice.
Our normal plow patterns position the trucks with their right steering and drive tires right on the strips when plowing the driving lane. This tears our traction chains up severely. When plowing the shoulder, the left steering tire and drive tires are on it, tearing up those chains. Also, the trucks that have shoes on the plow tend to drop the shoe in the strip with the result of damage to the shoe and damage to the strip.
There has been feedback from the oversize load and mobile home haulers that the position of the strip is where they often drive to allow for their width. It is often observed by the crew that these oversize units now drive further to the left, causing a safety issue with the passing traffic. The oversize units encroach on the passing lane and in the areas that there is a center median barrier this causes passing traffic to make adjustments. The oversize units then move to the right, crossing the strip and sometimes swerving their units.
When we perform slow moving shoulder activities, such as repair to sight posts and the cleaning of sight posts, our vehicle must drive in the strip. This chatters the vehicles apart. Traffic is often so heavy that we cannot straddle the strip. We have several activities that require us to drive slowly down the shoulder.
The sand from our winter sanding activities fill the strips. It is extremely difficult to broom out. When we do our spring brooming, we are anticipating additional costs in time and labor, as well as more wear on the broom.
Some information Larry shared on the strips was the depth of the milled groove is 5/8” (16 mm); the offset for edge line is 6” (150mm); groove center to center dimension is 12” (300 mm); this is the first winter after installation; the shoulder pavement is an open graded (“F”) mix. Larry had checked with CO, WA, MT and PA prior to their project and they reported no problems at that time.
I have replied back to Larry that I have not heard of other States having the problems as those identified by the Meacham Maintenance Section. In fact I have been reporting to others quite the opposite. Our evidence from New York , New Jersey and Northeast States show no deterioration of asphalt shoulder pavement due to rumble strip installation. Also water or debris does not collect in the grooves, because the air turbulence of the traffic (large trucks) keeps the grooves clean. An icy strip has not been identified as a problem. This is from experience with strips which have been in place for at least 5-6 years in the Northeast. Most States use a milled strip offset of 300 to 400 mm (12-16 inches) on the right shoulder; NH uses 770 mm. Maybe if Oregon used a wider offset (rather than 150 mm), then much of the unnecessary contact with the tires of maintenance and oversized vehicles may be reduced.
If your State has documented experiences similar to those outlined above or you have other comment to offer, I would appreciated hearing about them.
Thanks for your time........................Jim Growney, FHWA, ERC, Albany, NY
Thanks. I'll be anxious to hear. By the way, here is another issue we have encountered that has some merit.
Work crews closed the right lane on the interstate with cones on the skip. Next thing they knew, the cones were being knocked over. They report that rumbles on the left shoulder made folks shy away toward the skip and take the cones out. We found this out late in the contract, but made the adjustment to 18” (450mm) out from the fog line and no rumbles where there is median barrier 1 meter or closer. This would have helped the mountain situation, but, unfortunately, we had finished that section quite some time before.
Also, I got this note (good news) from one of our eastern Oregon maintenance foremen:
Hello Larry, My crew and I like the new rumble strips a lot and believe they have prevented many accidents from North Powder to Baker City. In the past few years we have averaged 2-3 deaths in this section of road. Since the rumble strips have been installed we have only had a few minor accidents. It sure has worked in our area. Brad
From: Jim Growney
Thanks for the good news too. If you get some sort of report on Oregon's experience (construction, maintenance, ROR reductions, etc.) it would be nice to put on the web. It sounds like putting the strips at a greater offset from the edge line as you are now doing will help some of the issues you bring up.
From: David Nicol
Delaware installed their first real rumble strips on I-95 this past fall. We've pretty had no snow yet this year, but based on the experience of our neighbors, we don't anticipate any problems. We used a 457-mm (18") offset from the edgeline, a 13-mm (0.5") groove depth, and a 305-mm (12") grovve c-c dimension. I think the 150-mm offset is too small -- as they have experienced, it will result in hits from wide or off-tracking vehicles.
From: Martin Calawa
What he is experiencing is the reason NHDOT chose to offset the rumble strips as much as they do. The rumble strips were position in NH specifically to allow the regular snow plowing operations to be performed without having the truck wheels in the rumble strips. If you notice in his email, he states that the snow plow truck wheels travel directly on the rumble strips and they use chains. He complained that the chains are being torn up, but the rumble strips are also. I think heavy trucks driving on the strips with chains would do significant damage to both road and truck (as apparently is happening). It seems to me that the only answer is to rebuild the rumble strips in the section of shoulder were the truck wheels would not normally ride on the strips. If there is as much damage to the strips as it sound, they have to rebuild them anyway.
The other problems he is having with the strips, like ice build up, could be do to damage they have already received. The reason I say this is that they state that the strips fill with water like a “trench of ice,” I don't think this would not happen if they were in good shape. It maybe that the pavement in between individual grooves is being broken out making a trench like condition along the length of the rumble strip. Moving the strip over slightly, further away from the travel lane, would also solve the oversized vehicle problems they are having.
From: Martin Calawa
How many States use chains on the wheels of their maintanance vehicles and run them over rumble strips? I think that maybe a significant factor for Oregon's problems.
From: Eric Worrell
NM maintenance crews in at least one northern district have indicated a problem with rapid deterioration of the shoulder near traditional “rolled in” rumble strips for coarser (aggregate) asphalt pavements. We believe this is generally due to freeze/ thaw and the fact that densities are typically lower in the vicinity of the rolled in rumble strip. Does Oregon use rolled or milled rumble strips?
The shoulder here is generally 5/8” below the driving lane because the driving lane almost always has an Open Graded Friction Coarse (OGFC) added to it that is not added to the shoulder. Thus the plow blade rides above the rumble strip slightly and doesn't beat on it too hard. I have heard the maintenance crews voice concern with this lower shoulder more often than with the rumble strips, but I'm certain if the shoulder was also covered with an OGFC they would be more concerned with the rumble strip. We have not yet placed a rumble strip in an OGFC but it has been talked about on a large upcoming project.
NM is switching to milled-in rumble strips partly because of the lower densities mentioned above. Also the milled strip should resolve any specific concerns with coarse aggregates. Because they will mill through/off the aggregate rather than roll into/around it, there will be fewer 'protrusions' for ice to grab onto. Also the wide shallow grove (in my opinion) should allow ice to expand or slide over the surface with less resistance and thus less deterioration.
We have noted standing water in the milled rumble strips although this appears worst with minimal cross slope (one route has rumble strips on the crown in a narrow median). I believe it will be less of a problem when a 2% cross-slope is used. There are concerns about hydro-planing or icing although I don't believe these safety concerns on the rare days that we have rain or snow in NM negate the great safety benefit derived for the rest of the time.
As far as trucks “blowing the water out” - this takes a significant volume of trucks and high speeds.
I personally don't feel entirely comfortable with using rumble strips on low speed, 2-lane highways. I think there is a great danger that a run-off-the road accident will be prevented only to cause a head-on with a significantly greater loss of life. Although I believe there is still a net benefit, I wish we could see more research on this and on the bicycle safety issue (on these low speed 2-lane roads typically chosen by bikes), which we seem to have much opinion about but very little concrete evidence. Also the concerns with oversize vehicles and maintenance in Oregon's statement seem most valid here.
I am going to forward the Oregon message to a couple District Maintenance Engineers and to one of the Traffic Engineers, Miguel Gabaldon, to see if they want to add to this opinion. Miguel has had some interaction with your website and in fact has discussed the standing water concern there. I have also suggested he become the (new) New Mexico contact for your web page although this is not official at this time.
This is Pat Fleming in Wisconsin DOT design, Madison, WI in central office.
We have been specifying a rumble strip offset of 2-1/2 feet from the edge of the traveled way for many of the reasons you mentioned cause a problem, on the outside shoulder and 6 inches off on the median side. We include rumbles on freeways and expressways only. On some expressways the Amish community use horse and buggy and the buggy can straddle the rumble as well, with no problem for the horses.
We are in the process, within 6 months, of changing from rolled-in rumbles to milled-in rumbles. With rolled-in we experienced premature deterioration of the asphalt in the rumble area, similar to your attached note. We feel because of the lack of compaction, or loosening of the asphalt once it has been compacted on rolled-in is one of the reasons for this. The rolled rumbles were inconsistent in depth which depended on asphalt temperature at the time of final rolling and occasionally weren't very straight. In Wisconsin, the rolled-in is 2-1/2 feet wide and our milled-in are 16 inches wide. The milled will allow a little more space for bicycles on expressway shoulders as well as being aesthetically more desirable.
As a former Assistant Maintenance Engineer, I have long been concerned that water could pool in the rumble strip recesses, then freeze and pop-out the asphalt as described in Oregon's experience. Since I am now Idaho's rumble strip contact, I decided to determine if there was any substance to my concerns. In January I contacted several of our district maintenance engineers to get their opinions regarding any maintenance problems they may have experienced because of rumble strips. I could not find anyone to confirm my fears. They indicated that the grooves are usually self-clearing (via traffic), and don't tend to pool water as I had envisioned. They have not experienced any other maintenance problems because of the rumble strips. Maybe there is a design/construction issue with the Meacham Pass rumble strips.
From: Bob McCarty
We also have a puddling problem here in Virginia but no damage as our winters are not severe enough to determine if we have a problem.
From: Bob McCarty
VDOT does not have any concern or plans to do anything since they just don't experience the heavy winter impacts. They do not suspect that there are any problems.
Depth in bituminous is 13 mm or ½”.
Shoulder slope is 5/8”/ft.
Also, you might talk with Chen to find out additional information. (804-786-2968)
From: Craig Genzlinger
I have not heard of any of these problems in Montana, but to be sure talked to some maintenance personnel. They confirmed that we have not had any problems with the rumble stiped area deteriorating - we mill them into our plant mix and then chip seal (no plant mix seals here). As far as plowing operations and concerns from trucking industry (ours are 6” off the edge lines) maintenance has been able to slightly modify their plowing procedures to be able to plow without running continuously on them. We did hear some minor complaints from a couple of trucking firms, but have not had much trouble since we explained why we use them where they are at. I have noticed companies that move houses (esp manufactured ones) run using more of the shoulder straddling the rumble strips.
If you or some maintenance people want more specific information, they could contact Dan Williams at MDT maintenance at (406) 444-7604. Any questions on design or placement and you can call me.
Hope this helps.
From: Robert Norburn
I contacted the FDOT State Roadway Design Office and they said that if there are any problems in Florida with any of the items mentioned in ODOT's message related to rumble strips, they haven't heard about them yet. This isn't surprising with the winter-related issues, but they also haven't heard of any problems related to oversize loads, and their Maintenance Office has also not reported any problems.
I also contacted the State Safety Office and this was their response related to the oversize vehicle issue:
There are similar complaints in Florida, but there has not been any noticeable change in the number of oversized trailer crashes on roads with these rumble strips that has come to our attention. We have always had complaints ever since we started allowing 14' wide mobile homes on the road. It may be that the perceived hazard is making drivers pass the 16.5' wide vehicles more cautiously thus safety results. We do not have an injury (long form) crash problem noticeable yet.
Title: RE: Rumble Strips and Freezing Conditions
We have milled in many miles of rumble strips and I have never heard of a problem. I do hear concern expressed by our Material Engineers in the Districts but still no evidence that we are having any deterioration. We will be adding them to two-lane roadways as standard practice starting this year.
Date: 03/03/1999 10:10 am (Wednesday)
I'm glad I had a chance to meet you at the ATSSA Convention in San Antonio. As I promised, I am attaching a copy of our rumble strip standard plan. I'm no expert on electronic graphics but I know it can be viewed with Acrobat Reader. Our switch to the ground-in rumble pattern is recent, therefore our statewide experience is limited.
In response to Oregon's dilemma, I offer the following; As you will see in our standard plan, our offset to the edge of the through lane is 300 to 600 mm. Our use of rumble strips are limited to freeways. We feel that at freeway speeds, their is insignificant delay in contact time with the rumbles caused by the 600 mm offset. I am not aware of any problems with ice build up in the strips. Nor am I aware of damage due to snow removal equipment (snow chains are not used in Michigan). Our Maintenance Division did express a desire to keep the offset at least 600 mm if possible. This was mainly to avoid having to ride the maintenance vehicle tire on the rumble. It was more of a nuisance concern than a safety or damage issue.
As I mentioned to you before, we have two projects where the contractors were allowed to demonstrate their ability to reproduce the ground in rumble pattern in concrete shoulders by hand forming methods. It produced the same audible warning effect as the machine milled rumble strips. We found the results acceptable and now allow this option for concrete shoulders. Rumble strips in bituminous shoulders are required to be ground in by machine.
We were approached with the concept of using a rumble pattern that is angled approximately 30 degrees to the roadway rather than 90 degrees. Some of the claims are that it reduces pull on the steering wheel and the machine has a higher production speed. Counter arguments are that the pull is insignificant and that it is due more to the break over angle between the through lane and the shoulder cross slope. It is also argued that the angled rumble pattern is not a deliberate product of the machine but rather an incidental product of the speed at which it moves. At this time, we will continue to use the 90 degree orientation. Have you heard of any other experiences with angled vs. 90 degree rumbles?
I will keep you posted on Michigan Rumble Strips.
Carlos A. Libiran
Design Standards Engineer