Why rumble strips on roads

Rumble strips have been used in advance of rural stop signs and prior to curves. In Iowa, transverse rumble strips are sometimes used on the approach to stop signs on rural roads. The Crash Modification Factors Clearinghouse provides the crash modification factors CMFs when installing transverse rumble strips as a traffic-calming device in urban and suburban areas. Rumble strips are used frequently in Iowa in advance of stop signs on rural roadways. Please note that their use in applications other than advance of stop signs is strongly discouraged by the Iowa Department of Transportation Iowa DOT.

Texas Transportation Institute, Rural Speed Management. Horizontal Displacement. In principle, the normal expected number of crashes can be obtained from the empirical distribution of a control dataset. The data available for this evaluation do not contain a proper control dataset for estimating the normal expected number of crashes, but instead rely on an EB approach developed for and often used in Swedish traffic safety evaluations [ 24 ].

The standard model values are based on the — period, which is the average before period Table 1. If rumble strips should be mandatory on 2 lane rural roads it is of major importance to gather the drivers experience and opinions.

To do this both qualitative and quantitative studies were performed. The qualitative study was based on focus group discussions intended to capture motorcyclist and commuter experience and opinions of milled rumble strips on narrow rural roads. The quantitative study was explorative and based on road-side interviews designed to capture the perceptions and experience of road users who had just travelled over roads with centreline milled rumble strips. The following section briefly describes the methods used.

Focus group discussions are a qualitative research method intended to obtain a wide-ranging description of how people reason about a specific topic or phenomenon [ 26 , 27 ], in this case, centreline milled rumble strips on rural roads.

Of the two stakeholder groups, i. Commuters were chosen based on the argument that these drivers are likely the most experienced ones, as they drive a lot and should therefore have more experience of driving on roads with milled rumble strips.

Before implementing the focus groups, participants received written invitations that also contained information about the project. The discussions were relatively structured and followed an interview guide [ 28 ]. The discussions were voice recorded.

The analysis was thematic note based and the voice recordings was used as a support to the notes. The motorcyclist focus group comprised six motorcyclists, one woman and five men, 30—55 years old. They were recruited through personal contacts. The discussion took part in August and lasted in total for approximately 3 h. The rumble strips applied on this part of the road is a typical solution in Sweden.

The rumble strip has width of 30 cm, a length of 15 cm, a cc of 60 cm and a depth of 1. Before the start an information meeting was done at VTIs premise. After the information, the riders were asked if they had questions and informed that they had they right to stop without reason at any time. The group then drove the 40 km together. The moderator and observer travelled as passengers.

The interview guide was only used when needed and it consisted of questions in the following areas: experience from driving on rumble strips, their thoughts about the aim with rumble strips including questions about pros and cons, safety and accessibility , design of the rumble strips, acceptance and future recommendation. The group of car commuters comprised four people, i. They were recruited thru advertisement in the local newspaper and through personal contacts.

The discussion took part in November at VTIs premises. Before the discussion started a short round the table presentation was done and information was given about the aim with the focus groups and a small presentation about the rumble strips. The discussion lasted for approximately one hour.

Participants took different routes to and from work, but all drove on roads with centreline milled rumble strips during their daily commuting. Three participants were shift workers, while one travelled considerably while on duty, often late at night. Coffee and tea was served during the event. The roadside questionnaires were administered along roads with centreline milled rumble strips, i.

To contact passing drivers, the police stopped drivers randomly to check driving licenses and test breath alcohol levels. The site selection depended on police officer availability and on the appropriateness of stopping road users.

Then drivers were asked whether they were willing to participate in the study. If they agreed, the interviewer approached the car and asked if they agree to answer a limited number of questions. The surveys were completed by the interviewer.

Most drivers agreed to be interviewed; some drivers declined, usually because they had a deadline to meet. The results of the Empirical Bayes analysis, correcting for RTM as well as the general road safety trend and changes in traffic volumes are shown in Table 2. No significant changes are noted in injury crashes. The EB approach relies on standard model values i.

In general, the observed FSI rate is lower than the standard model value. For injury crashes, the difference between the observed rate and standard model value is small for normal-width roads, while the observed rate is lower than the standard model value for narrow roads.

The results of the focus group discussions indicate that rumble strips are not perceived as a problem by either motorcyclists or commuters, taking into account both traffic safety and accessibility. The participants had no objections to the design of the rumble strips or to how they influence driving, although they thought that a road design with even deeper rumble strips, for example, might be even more effective.

Two members of the group of motorcyclists said:. Low-quality tires and low tread depth seemed to increase the effect of the rumble strips perceived by the motorcyclists, who also commented that motorcycles without rear shock absorbers definitely registered the effects of rumble strips more than did normal sport bikes.

Despite this, the motorcyclists did not seem to be influenced at all by the rumble strips, unlike the commuters, who mentioned their influence not only on their speed but also on their lateral lane position.

The commuters described how they changed their driving behaviour, for example, overtaking less often and shifting their lateral lane position to the right i. A driver from the commuter group said:. You take less risk in this way. The average age of drivers was 50 year SD On average, the drivers had possessed their driving licenses in 31 years SD Among drivers 23 reported high levels of sleepiness KSS 8—9 during the driver.

All of them except one agreed that rumble strips would contribute to traffic safety. For those remaining drivers with less degree of self-reported sleepiness believed the rumble strips would contribute to traffic safety, and 20 drivers did not. The difference between the groups was not statistical significant. It was also shown that road users, especially the motorcycle riders, were positive about the rumble strips.

The interviewed experienced commuters were also positive about the rumble strips, even though they thought the strips would force them to reduce their speed and overtake other cars less often. The criteria for selecting roads for the installation of rumble strips did not include a high crash record of the road, and the results of this study indicate that the crash rates observed in the before period were lower than expected from the standard modelled values, leading us to suspect regression to the mean RTM effects [ 21 ].

The slight difference between these results, although they all tend in the same direction, might be due to different rumble strip designs. In our study, only conventional milled rumble strips were examined; it is not known what sorts of rumble strips were examined in some of the other studies.

The differences in results might also depend on how and whether RTM is considered. In this study, considering RTM makes a large difference for the numbers of fatalities and seriously injured people, but for all injury accidents. Other aspects that might explain the inter-studies variability are road features and cultural differences. In the ITERATE-project where a unified model of driver behaviour was developed, it was found that country or possibly culture was a significant factor for almost all performance indicators [ 31 ].

However, it was not further investigated which aspects differed between drivers from different countries. It has also been shown that road width might affect the safety benefits. In an earlier study larger effects were shown for narrow roads with road width below eight meters compared to roads 8—10 m wide [ 32 ]. The results of our study are supported by analyses of crash scenarios based on detailed police reports from the Swedish crash data system STRADA.

These analyses indicate that centreline milled rumble strips reduce the risk of multi-vehicle collisions and crashes in which a driver drives leftward off the road [ 33 ]. Simulator studies also demonstrate that rumble strips are effective in awakening sleepy drivers and that drivers awakened by rumble strips take the proper countermeasures [ 14 , 17 ].

Most studies examine rumble strips used in the centre of 8—m-wide roads, though they could also be used in the centre of the lane. Pre-pilot tests have examined such a possibility, and though their results were positive, motorcyclists complained that such strips influenced and reduced their ability to follow the road as desired. Finding a solution to these problems calls for further investigation. Another issue is that it is more and more common with in-vehicle Lane Departure Warning systems with the aim to reduce single vehicle and head-on crashes, and that an increasing rate of cars with LDW systems has affected the results in this study.

Longitudinal rumble strips can also be used in the centre of the road. When combined with painted centrelines, rumble strips help prevent head-on crashes and run-off-road crashes resulting from vehicles crossing into the opposing lane.

Flexible posts or flexi-posts can also be used in the centre of the road to separate opposing flows and are an effective treatment in discouraging overtaking manoeuvres, reducing the likelihood of head-on crashes. Reduced run-off-road and head-on crashes. Improved visibility of edge lines or centre lines during wet weather.

Potential for reduced maintenance of road shoulder. Advanced warning to hazards. Where used on high-speed roads, transverse bar markings have been shown to reduce speeds on approaches to intersections such as roundabouts. Longitudinal rumble strips may be a hazard to cyclists and motorcyclists. Gaps in the rumble strips may be needed in some areas to allow water to drain from the road surface.

The noise made by rumble strips can be difficult for drivers of larger vehicles to hear.