Why are these pretty oleander shrubs so common on motorways and dual carriageways in Spain?

The majority of safety items found on main roads, dual carriageways and motorways in Spain are usually limited to signs, crash barriers or speed cameras. All of these help facilitate traffic flow and establish order for drivers on the road.

However Spanish motorways and dual carriageways often have vegetation planted in the central reservarion. The most common type of plant is oleander. According to the Spanish Royal Academy dictionary, it is defined as a "shrub of the Apocynaceae family, poisonous, very branchy, with persistent leaves similar to laurel and clusters of white, reddish, pinkish or yellow flowers". With this explanation, you are probably wondering why this type of plant is often chosen to be planted on main roads.

Oleanders are quite leafy and help to keep oncoming cars out of sight. This is beneficial, especially at night, to avoid glare from headlights on other vehicles travelling in the other direction on the opposite carriageway.

Another use for these shrubs is to serve as a "cushioning barrier" for a vehicle that runs off the road, so that it does not have such a heavy impact on those passing on the opposite side of the road. "Oleanders would reduce the severity of the impact by absorbing part of the vehicle's kinetic energy and redirecting its trajectory," according to the website Circula Seguro.

However, just as oleanders can help in many ways, there are some disadvantages to using these plants. Oleanders and their robustness could be dangerous in the case of impact or a car coming off the road, contradicting the possibility that they would absorb the blow. This will depend on how big and strong the branches become.

On the other hand, poor maintenance of oleanders and their location too close to the road can cause their branches to rub against vehicles, which can cause damage to the bodywork. In addition, overgrown roots can deform the edges of the road. The leafiness and proximity of these shrubs to roads also produces another disadvantage, the "tunnel effect" on drivers, which could make them lose their sense of the real speed at which they are travelling. Another disadvantage would be that an oleander can obscure the presence of an animal preparing to dart across the road.