General description and targets

Fences are erected to prevent the access of animals onto roads or railway lines. They are mostly constructed to reduce accidents due to collisions between large mammals and cars, but also to reduce the number of smaller animals killed on the roads. The disadvantage of fences is that they increase the barrier effect. Where fences or other barriers are erected, it has to be ensured that the species concerned have enough opportunities to cross the road or railway line. In most cases, fences must therefore be combined with wildlife passages. In these cases they fulfil an important role in guiding animals to the crossing points. When traffic safety is not an issue fences should only be erected where animal mortality might threaten a population otherwise the barrier effect might have worse effects on the survival of the populations in the long term than the mortality due to traffic.

Location

• In general, wildlife fences should be erected only in places where the number of animals killed is high or where there is a high risk of accidents involving wildlife. This is mostly the case along high-speed roads and railway lines. On ordinary roads with low traffic density fences should only be erected at highrisk spots.
• The surrounding landscape has to be checked with respect to other fences or barriers to animal movement: creating new traps between parallel fences has to be avoided, and the number of fence lines should be reduced wherever possible.
• Fences should always be built on both sides of a road or railway line. The ends of the fences are danger points: animals may go round the end of the fence and get trapped on the road. Fences should therefore end at structures like bridges. Where only a stretch of the road is fenced in they should be extended 500 m or more beyond the danger area.
• On roads with relatively little traffic, openings in fences can be provided at locations where animals can easily cross and where crossing animals are well visible to drivers.
• In areas where natural habitats for animals have been reduced to small patches, any potential habitat should be made available to the animals. From the point of view of the animals, a fence should therefore be placed close to the road to reduce the amount of inaccessible area along the verge, thus allowing animals to use the verge as a habitat or movement corridor. However, the location of the fence in relation to the road has to also take into account aspects of traffic safety and road maintenance.
• Where a road is built on an embankment with a wide slope it is preferable not to put the fences at the foot of the slope but at the top or halfway up, depending on the local situation. The same applies to cuttings. • Particular attention has to be paid to the placing of fences in relation to fauna passages and other possible crossing points for animals. Fences must not block entrances to passages nor provide traps, but they do have an important function to guide animals towards passages. (See also Sections 7.2.1 and 7.3.2)

Design

Conventional wildlife fences consist of wire mesh fixed with poles. Height and mesh size depend on the target species. In order to be an effective barrier, a fence has to meet the following requirements:

• The height should be such that animals cannot jump over it.
• The wire mesh has to prevent animals from passing through the openings.
• The mesh has to be fixed such that animals cannot pass under the fence. • Electric fences are expensive to run and need frequent checks and maintenance. They are not an option for long stretches of road, but may be considered locally where a high risk exists for endangered species, and can be used temporarily to train animals to change their habits after a new road is built. 

Height

• The height is determined by the occurrence of different ungulate species: Red deer, fallow deer, moose: minimum height: 2.2 m (preferably 2.6-2.8 m) Roe deer, wild boar: minimum height 1.5m (preferably 1.6-1.8 m).
• The height has to be adjusted to the terrain and is measured on the side of the approach of the animals (see Figure 7.79). Where the approach of the animals is downhill, this adjustment is essential.
• In areas with snow cover, the minimum height has to be guaranteed in winter as well.

Mesh

• For conventional wildlife fences, a smaller mesh size in the bottom half or third of the fence is recommended. Distance between horizontal wires: bottom: 50-150 mm, top: 150-200 mm. Distance between vertical wires: 150 mm. • Wires should have a diameter of at least 2.5 mm and should consist of rust-free material.
• In areas with heavy snowfall, the top wire of the netting must be reinforced with a cable capable of bearing the weight of the snow settling on it.
• The bottom wire should lie directly on the ground and be fixed to prevent animals from crawling under the fence. Burying the wire mesh 20-40 cm under ground may be necessary in areas with badgers or wild boar. Where the ground is uneven, it has to be levelled out to avoid gaps e.g. due to holes in the ground. Special care should be given to places where fences cross ditches.
• The wire mesh should be fixed on the outside of the poles (i.e. away from the road) to prevent mesh from falling away from posts when large animals crash into fence.

Poles

• Metal or wooden posts are both suitable.
• Poles have to be strong enough to withstand the impact of an animal in flight running into the fence. End posts should have a diameter of 2-2.5" (steel) or 10 x 10 cm / 12 cm diameter (wood). Middle posts can be slightly thinner. Poles should be replaced when they are damaged.
• All posts must be firmly embedded in the ground (approximately 70 cm or more depending on the ground).
• For deer, the distance between posts should be 4-6 m (up to 10 m in flat areas), for wild boar 4 m maximum.

Exits

• Where there is a danger that animals might get trapped on the road, i.e. particularly when the whole stretch is not fenced, exits should be provided to allow the escape of animals.
• It is better to avoid the Dutch type of exit doors for badgers or any other mechanical doors. Experience has shown that they often stay open or become damaged.

Additional considerations for small animals

• Fences to keep out small animals (amphibians, reptiles, small mammals) should only be erected in conjunction with passages. Otherwise, small animals should not be kept away from road verges completely, because these often provide suitable habitat and serve as movement corridors for these species. Only in cases with high road mortality is it justified to keep species like tortoises or lizards away from the road areas.
• To keep out small animals an additional mesh can be fixed to the standard fence. Depending on the species mesh size should not be greater than 2 x 2 to 4 x 4 cm. Height: 40-60 cm. To prevent animals from climbing over the fence, the top part should be turned out- and downwards.
• For amphibians opaque barriers instead of wire fences are recommended. These are discussed in Section 7.3.7.

Maintenance

• Fences have to be checked in detail as part of ordinary road inspection at least once a year and more frequently during the first year.
• Particular attention has to be paid to:
  - holes (which have to be repaired immediately),
  - attachment to the poles,
  - attachment to the ground,
  - trails and hollows which indicate the regular passage of animals under the fence. 
• If fences are damaged by cars after accidents or after storms, they have to be repaired immediately.

Points for special attention

• Fences are effective barriers for most, but not all species: wire fences effectively hinder the access of deer, wild boar, hares and other non-burrowing and nonclimbing species, but brown bears, lynx, martens and others are able to climb over most fence types. Burrowing animals like badgers and foxes may force under a fence if the fence is not fixed underground.
• Where gates have to be provided to allow access to the road or railway line, their design has to be such that only gaps as small as possible exist between the gate and the ground and between the gate and fence.
• A dense row of bushes planted close to the fence on its outside can prevent mammals from attempting to jump across a fence. No plant species attractive to foraging animals should be used.
• All small bridges, underpasses, culverts and other possibilities for joint-use fauna passages across the highway have to be accessible by animals from the outside of the fence.
• Where narrow access roads require an opening in the fence cattle grids may provide a barrier to larger animals. However, they are a danger for small animals that easily fall in. They should therefore be equipped with escape ramps. A hole in the side of the base of the cattle grid can also help to avoid victims.

Artificial deterrents aim at keeping mammals away from roads or railway lines in order to reduce the number of collisions. They are mainly targeted at deer. Various systems exist based on optical, acoustic or olfactory devices. Experience shows that the effectiveness of such measures is usually very limited. Reflectors/mirrors Wildlife warning reflectors are widespread.They consist of various types of metal strips placed around trees or other structures. The light of approaching vehicles is reflected towards the side of the road, which should warn animals and stop them from entering the road. These features are popular because they are cheap and easy to place. However, a thorough analysis of studies carried out over the last 40 years all over the world found little evidence for the effectiveness of wildlife warning reflectors. Reflectors also require a lot of maintenance.

Acoustic deterrents Ultrasound devices emit acoustic signals that should deter mammals. Like other acoustic deterrents there is no evidence for their effectiveness. Olfactory repellents Olfactory repellents are a relatively new measure to prevent accidents, mainly involving deer. Natural or artificial substances, usually a mix of scents from humans, wolves and other predators, are injected into a foam as a carrier substance which is then applied to trees or posts in the vicinity of the roads. The first tests of these relatively new systems indicate that the number of collisions with cars is effectively reduced. Observations seemed to show that deer increase their attentiveness and thus may become more aware of approaching cars. When there were no cars around, the animals crossed the roads. Other observations indicated, however, that while deer crossed less in the treated stretches of the road, they shifted to adjacent untreated areas. To prevent habituation by animals olfactory repellents should only be placed during critical periods, e.g. during the migration period of deer. Further research is needed to show the effectiveness of these measures in the long term. More experience is needed with regard to maintenance needs. The possible impact on non-target species is unknown.

Warning signs aim at influencing the behaviour of drivers in order to reduce the number and severity of collisions between large mammals and cars. Standard traffic signals are placed in areas where collisions often occur. They also exist for amphibians, waterbirds and other animals. However, research has shown that drivers don't pay much attention to signals on their own and in particular don't reduce their speed. Therefore systems have been developed to increase their effectiveness.

Location

• Wildlife warning signs should be placed only in places where there is a high risk of collisions, because the more widespread they are, the less people pay attention to them.
• Putting up signs only during critical seasons could make people more attentive to them.

Points for special attention

• The combination of a wildlife warning sign with a speed limit is slightly more effective.
• The effectiveness is further enhanced if signs are marked with flashing lights or a flashing speed limit sign, which are lit only during periods of high animal activity.

Wildlife warning systems combined with heat sensors have shown to be able to reduce the number of collisions. Heat sensors in the vicinity of the roads detect approaching mammals up to a distance of 250 m. The sensors trigger the fibre optic wildlife warning signs which are combined with speed reduction signs (30-40 km). Normally the signs appear dark and the light points are only visible when activated. The system can be powered by solar energy. Wildlife warning signs without speed reduction are less effective.

Points for special attention

• People should be informed about the way the combined system works, because only if they know that an illuminated sign does not only indicate a potential danger, but also the actual presence of an animal, will they adapt their behaviour.
• Warning signs should be combined with speed limits.
• Like any other technical equipment, the combined system has to be checked regularly.

General description

Different ways of designing and managing habitats alongside roads and railway lines are used with the aim of reducing the number of collisions. Some are designed to prevent animals from moving onto the road surface by attracting animals elsewhere, others by influencing the behaviour of animals or by making animals more visible.

Cutting of vegetation

The cutting of bushes and trees within a 3-10 m strip alongside the road reduces the attractiveness for large mammals such as moose. At the same time the visibility of the animals to drivers is improved. The measure is designed to reduce the number of collisions between large mammals and cars. This measure is suitable for roads with low traffic load and for railway lines. Verges with short vegetation often have high densities of small mammals (rodents) and are therefore attractive to birds of prey. This may increase the risk of collisions with birds.

Choice of plant species

The choice of the right plant species to be planted alongside roads can reduce the number of collisions between cars or trains and animals. While it is advised to use native plant species, care should be taken to avoid plants which may attract animals to the road verges for foraging, increasing the risk of collisions with cars: 

• Bushes and trees, which are not attractive to browsing deer, etc.
• No bushes with attractive berries, in particular not in the central reservation. Berry bushes attract songbirds, mainly during migration.
• Forest fires often start from roads. Plant species that burn easily should not be planted to reduce the risk of fires spreading to adjacent habitats.

Hedges

• Hedges along fences can lead animals towards fauna passages. A gap between the fence and the hedge facilitates maintenance work along the fences.
• Bushes alongside the fence reduce the danger that large mammals try to jump the fence.
• Tall tree hedges force birds to fly high. Thus they cross the road at a height where they don't collide with cars. On the other hand, hedges may attract birds to the vicinity of the road increasing the risk of collisions.
• The planting of hedges has to consider the above-mentioned points of visibility and choice of food plants.