The Nordic Conference on Road Marking was organised on 8 - 9 February 2011 in Rovaniemi, Finland. One of the conference themes was the participant countries’ reports on their R&D activities. The Finnish presentation focused on the safety and behavioural impact of audio tactile profiled (ATP) lane markings and wider marking areas in the central reservations of dual carriageways.

Head-on collisions are in many cases fatal. It is quite evident that the most effective solution for preventing these accidents is to keep the vehicles travelling in opposing directions separated by structural means, such as crash barriers. As this option is not always feasible, at least not in the near future, we must find other solutions applicable to the extensive road network.

The purpose of ATP markings, or rumble strips, is to reduce the number of accidents due to the driver's diminished attention or errant driving. The ATP markings generate sound and vibration when the wheels come into contact with the strip, alerting the driver that he or she has crossed the lane boundary line.  As a working hypothesis, it is reasonable to assume that an ATP centreline will reduce the number of head-on accidents and instances of a vehicle traversing into the oncoming lane and, correspondingly, an ATP edge line will reduce run-off-road accidents on the right-hand side.

ATP markings have been laid in Finland on over 5,000 kilometres of road, most of them since 2006. The guidelines issued for the use ATP markings are based on the traffic volume and the width of the highway. Centreline ATP markings have been laid on over 3,000 kilometres of road, edge line ATP markings on approximately 1,500 kilometres of road, and both together on over 600 kilometres of road.

The report by the Finnish Transport Agency (Studies and Reports 41/2010) examined the correlation between ATP markings and the number of road traffic accidents. The number of single-vehicle and head-on accidents having occurred prior to laying the ATP markings was compared with the number of accidents following the laying of the markings.

Two methods were applied in the study for assessing the traffic safety impact:

1. The number of accidents in proportion to the traffic volume (accident rate) was calculated using the pre-post assessment method for both the roads with ATP markings and the comparison group roads, where no significant change took place during the review period. The change in the relative accident rate in the comparison group data was then deducted from the corresponding change on the roads with ATP markings to provide the impact value.
2. The effective accident volumes and empirical Bayes method were used to calculate an optimally reliable prediction of the accident volume for the pre-ATP period and the comparison group roads. This allowed better control, among other things, over any potential error due to the regression to the mean effect that may be contained in the accident volumes data. Hereafter, we calculated an estimate of how many accidents would have occurred in the absence of the ATP markings, using a combined model. The accident volume thus obtained was compared with the effective post-ATP accident volume observed.

The results indicate that, on the roads with ATP centrelines, the number of personal injuries in head-on accidents and the vehicle traversing into the left-hand side were reduced by 18 per cent more than similar accidents on the roads without ATP markings. The change projected by the accident prediction model was not quite as great, since ATP markings had been laid, to some extent, more on highway sections where the occurrence of accidents exceeded the average. On these grounds, the ATP centreline is estimated to reduce the number of head-on accidents and the vehicle traversing into the opposing lane by 10 per cent.
In the case of the ATP edge line, the data was not sufficient to produce a reliable estimate, but, in view of the results, it would appear that the ATP edge line reduces the number of run-off-road accidents onto the right-hand side by 10 - 20 per cent.

The results demonstrate that the ATP markings benefit traffic safety and their use is justified in the future to reduce accident volumes. In principle, the existing guidelines allow the laying of an additional 3,000 linear kilometres of ATP marking on main highways.  Based on the study results, this would prevent approximately twelve accidents involving personal injuries per year.

Experiment on wider marking areas in the central reservations of dual carriageways

In terms of traffic safety, the critical factor is in many cases how much reaction time the driver has to perform the various functions related to driving. When two vehicles coming from opposite directions meet on a divided highway, the reaction time is minimal, should anything unexpected happen. The reaction time allowed for the driver can be increased through keeping the vehicles travelling into opposite directions further apart from each other using road surface markings.

Experiments were initiated two years ago on Highway 3 between Laihia and Helsingby and on Highway 23 between Söörmarkku and Noormarkku using road markings, which deviate from the standard markings in three respects (Image 2):

1. The distance between the two centrelines is approximately 1 metre instead of 10 centimetres so as to increase the distance between passing vehicles.
2. Two white centrelines are used instead of a single one in cases where overtaking is allowed in both directions, thus keeping the guidance effect of the markings consistent throughout the highway section.
3. The width of the centrelines is 20 centimetres instead of 10 to improve visual perceptibility of the centreline.

A wider median-area road marking requires, at a minimum, a surface of 9.5 metres in width to allow adequate walking and cycling space on the shoulder and to prevent any increase of run-off-road accidents onto the right-hand side.

In connection with the experiment, driver behaviour was studied both before and after laying the new markings. The experiment included measurement of spot and travelling speeds, the vehicle's horizontal position in the lane, and the number of overtaking manoeuvres on the test highway sections. Interviews were also conducted to find out the drivers' views about the new marking practice.

The key findings provided by the experiment’s measurement data were:

• On the test highway sections, the distance between opposing driving directions increased, as expected, by approximately 1 metre.
• The increased distance was estimated to increase the driver’s allowed reaction time in a head-on situation by 0.4 – 0.8 seconds (at a speed of 80 km per hour and the traversing angle being five (5) degrees). The increase in the driver’s reaction time can be considered to promote safety significantly, since the widely accepted reaction time is two (2) seconds (at a speed of 80 km per hour).
• Average spot speeds were reduced at night by 0.5 km per hour (as measured one (1) year after the marking was laid).
• No impact on the number of overtaking manoeuvres in summer was observed. In winter conditions, the situation may be different when the quantity of snow or slush accumulated in the central reservation increases.

The interviews indicated that the drivers have a positive attitude toward the new marking practice. Over 80 per cent of the drivers interviewed at the experiment sites considered the road marking to be beneficial in terms of traffic safety, and approximately 75 per cent of all interviewees were in favour of increasing the use of the wide central reservation marking.
The drivers interviewed also considered the road marking to be clear and easy to interpret.

Based on the results, the wide central reservation marking will most probably allow for the prevention or mitigation of head-on collisions. A more extensive use of the wide central reservation marking requires nevertheless further monitoring of the sites and adding of new highway sections to the experiment to validate the obtained positive results. Our intention is to include this year’s two new sites within the scope of the experiment. At these sites, a new method for laying rumble strips will be tested. A solid groove of sinus curve profile milled in the surface will allow for the reduction of environmental noise compared with an interrupted series of grooves, yet they also produce a nudge effect on the driver departing from the lane. Furthermore, the groove will be milled on both sides of the mid-seam throughout the highway section to safeguard the damage-prone surfacing seam and to increase the nudge effect. The road markings are also expected to be more discernible, and to remain in a better condition in a solid groove, thus improving, for instance, the operating conditions of the lane departure warning systems mounted on vehicles.

Sources:

Täristävien tiemerkintöjen turvallisuusvaikutus. Liikenneviraston tutkimuksia ja selvityksiä 41/2010. Leveän keskialueen tiemerkinnän vaikutukset kuljettajien käyttäytymiseen ja mielipiteisiin. Tiehallinnon selvityksiä 39/2009.

Material from the Nordic Road Marking Conference 2011:
http://www.nmfv.dk/Konferencer/Konferance_Rovaniemi/ NKV_program_2011.htm.