More effective protection in collisions with trees

Jun 2017


A continuing problem in Germany and other countries is collisions with roadside trees. Accidents of this kind frequently have grave consequences. According to information from the Federal Statistical Office (Destatis), in 2015, 603 people in Germany were killed in road accidents after collisions with a tree. This accounts for around 17% of all 3,459 road users killed. Rural roads carry the greatest risk. Here, in 2015, 517 people were killed in collisions with trees in Germany, equivalent to around 26% of all traffic fatalities on rural roads. In comparison, in 2015, 2,175 people were killed in road accidents on rural roads in France, 316 of which were collisions with trees. This is equivalent to around 15%. In Italy, the problem appears to be slightly less severe. In 2015, 1,495 people were killed in rural road accidents, 127 of which were collisions with trees, which is just under 9%.

The risk of being killed in a collision with a tree is generally twice as high for the occupants of cars compared with other obstacles. In a collision with a tree, all the impact energy is concentrated on a small area of the vehicle. The occupant safety elements in-built in the vehicle therefore have limited effect, resulting in a very high risk to the occupants. Today, infrastructure measures hold huge potential for minimizing the number and consequences of accidents involving collisions with trees on the side of the road.

When new roads are built and trees planted, a roadside safety zone, as already seen in some Scandinavian countries, should be planned. If this is not possible or possible only to a certain extent, suitable restraining systems should be installed, even on existing roads. Two-wheeled drivers can also be effectively protected by suitable designs.

Optical guidance systems situated on or right next to the road can improve visual guidance, as can yielding guidance posts fitted with reflectors. Bushes and shrubbery are also an environmentally friendly and safe road design measure because they ensure that vehicles are stopped by something large and relatively soft. Damaged or destroyed trees should not be replaced. Along hazardous stretches of road, trees should be removed from the roadside and replanted at a safe distance from the road. At spots where trees are a known hazard but it is not possible to replant the trees, not only crash barriers but also impact attenuators that provide a larger surface against which a vehicle collides and that deform in order to absorb additional energy could potentially be used.

Speed limits and overtaking bans can also help to improve safety on stretches of road with a high number of accidents, provided such measures are properly monitored. A good example of this can be found in the German state of Brandenburg, which has a high number of tree-lined roads and, consequently, a high number of fatalities as a result of collisions with trees. In 2015, almost 40% of all road traffic fatalities occurred following collisions with trees (in figures: 69 of a total of 179). Compared with 2014, during which 54 people were killed in collisions with trees, this represented an increase of almost 28%. But the situation improved significantly in 2016. According to preliminary figures, the number of fatalities as a result of collisions with trees fell from 69 to 30, a decrease of almost 60%. This can most likely be attributed to the fact that Brandenburg had introduced, among other measures, a speed limit on all tree-lined roads where no roadside crash barriers were installed. Where before the limit was 80 km/h or 100 km/h, it is now 70 km/h. Another reason for this significant reduction in the number of fatalities from 2015 to 2016 could be the fact that additional crash barriers had been extensively installed along tree-lined roads and on certain trees.

Speed surveillance measures

In many countries, speed limits that are now legally standardized – 30 km/h in residential areas, 50 km/h on main roads, 65 km/h to 100 km/h on country roads and 100 km/h to 130 km/h on high ways – are the basis for the largely safe coexistence of all sorts of different modes of transport. The management authorities responsible can also erect special traffic signs stipulating additional, location-specific speed limits.

But the simple imposition of speed limits does not lead to greater safety – road users have to actually stick to the rules in order for the desired effects to be achieved. Therefore, drivers have to know that they may be caught and punished if they violate speed limits. All over the world, a wide range of different surveillance methods have been implemented – from having police officers estimate how fast a vehicle was traveling, through local surveillance with measurement devices, to a variety of air surveillance methods. A great deal of variation also exists when it comes to the level of penalties imposed. In some parts of Canada, for example, exceeding the speed limit in non-urban areas by 20 km/h could result in a fine of around €20; in Switzerland, however, the same offense could see you landed with a fine of at least €240. The greater the speed by which drivers exceed the speed limit, the greater the punishments can potentially become – for example, drivers risk having their vehicles impounded or even facing prison. The level of punishment is frequently left to the discretion of the police officer(s) that issued the warning. Many countries also have points systems, whereby not only serious, one-time infringements but also multiple relevant infringements can result in drivers having their driver’s license revoked, at least temporarily.

The first mobile speed surveillance radars were introduced 60 years ago. These allowed vehicle speeds to be accurately determined in either a stationary or mobile installation. The risk of measurement errors was minimal provided that the systems were used properly, and so the technical basis at least for ensuring fair punishment for speeding had been established. Over time, speed surveillance systems became ever more sophisticated.

The Australian state of New South Wales broke new ground by introducing a zero-tolerance policy to speeding. In terms of ensuring the safety of pedestrians, even small reductions in speed can play a big role. Zero or near-zero tolerance to speeding among stationary and mobile speed camera installations is therefore designed to reduce overall speed in built-up areas. Simply calibrating speedometers so that the displayed speed is higher than the actual speed should ensure sufficient tolerance.

Who is responsible for speed surveillance, and by what means, varies across the world. In certain regions, the police alone might be responsible for speed surveillance; in other regions, the relevant regulatory authorities and even municipalities themselves might also be authorized to install speed cameras. However, problems can arise if the body responsible for surveillance also profits directly from the revenue. In this case, clear legal specifications must ensure that traffic surveillance measures are appropriate and do not serve simply to tell the coffers of the body responsible for surveillance. I veillance. In some countries such as France, traffic surveillance is permitted only within defined zones. Often, upcoming speed checks must be announced in advance on specially erected signs. In other countries, however, it is forbidden for the location of stationary speed cameras to be indicated in navigation systems or speed camera warning apps for cellphones.

So-called “speed camera marathons” are also becoming increasingly popular. Announced in advance and generally enjoying high media attention, speed camera marathons are organized on certain days of the year at either regional or national level and place the focus of traffic surveillance measures on speed over a 24-hour period. Members of the public are often invited to name specific roads or sections of roads where, in their opinion, speed controls might be particularly beneficial. Experience from other European countries shows that campaigns like this enjoy a high profile and are well received by the public. Whenever speed camera marathons are held, the number of people caught speeding is very low.

A major problem with the systematic punishment of road safety violations is the risk of corruption. Particularly in certain developing and newly industrializing countries, such tendencies can be seen. In consequence, motorists do not see the purpose of traffic surveillance, meaning that even the imposition of fines has no effect whatsoever on improving road safety.

One method that has proved especially effective is the use of “dialog displays”, particularly at spots where compliance with speed limits is especially important such as where roads enter towns or villages, in front of schools and kindergartens or at pedestrian crossings. Here, drivers get to see their current speed displayed on a large board along with, for example, a happy or sad face. A raised, admonishing index finger in conjunction with an emotional display, or some form of direct and immediate congratulations for sticking to the speed limit visible to all drivers and not just the driver being praised, are often much more effective at instilling safe driving habits over the long term than speeding tickets.

Crash test car colliding with a tree


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