The choice of metal protections to be used in a road safety project should follow regulations established according to ABNT standards. Currently, the road market in Brazil is regulated by NBR15486, which provides for traffic safety by establishing the guidelines for the projects of road containment devices and determining the requirements for the crash tests.
If the choice of a metal protection, popularly known as guardrail, is well done, there will not be unnecessary expenses with road project. In contrast, if the selection is made following the standardization adopted before NBR15486, the road stretches will be sub or oversized and, consequently, compromise the cost-benefit of the project.
However, in order to optimize a road project, even before defining which guardrail should be used, it is necessary to evaluate whether there is a real need to use such device. The professionals involved in a road project must communicate so that the best choices are made without prejudice to the development of this project.
In order to avoid possible mistakes in the planning of a road project, we will explain below which criteria should be taken into account by designers.
Integration between designers
If – during the initial phase of a project creation – occurs the integration of the designer responsible for the geometry of the runway, the drainage designer and the road safety and signage designer, a great deal of expenses can be reduced or even eliminated.
As an example, we can use a drainage design with a perfect concept and volumetric calculation, but it may pose a risk to road users. In this case, perhaps a different solution is to eliminate the protective expenditure of that obstacle within the free zone.
Concept of a forgiving highway
Regardless of the reason for a vehicle leaving the raceway, the goal is to have an obstacle-free side environment, with steady and stable slopes, in order to reduce the severity of accidents.
Is there a need to protect the entire highway?
Before defining that it is mandatory to install a guardrail, it is essential to ensure an optimized project, to check that the obstacle within the free zone can:
- be removed;
- be redesigned to ensure safe crossings;
- be relocated out of the free zone;
- make the obstacle collapsible, if possible.
- protect the obstacle;
- signal the obstacles if none of the above are not possible.
Need for containment devices
In several situations of works already executed, it is necessary to protect the obstacle, but a concept needs to become clear. The designer should be concerned with protecting the users first and not the obstacle itself. This phrase seems obvious, but in many cases we find distortions in this concept.
The containment barrier, whether it be a metallic or any other type of protection, is intended to redirect the vehicle to the lane in the safest possible way, thus minimizing the risks to drivers and passengers traveling through that stretch or to some vulnerable highway users.
What demands the need for containment devices
As required by NBR15486 of 2016, it is necessary to install containment devices on stretches of a highway that have within the free zone the following untreated examples:
- fixed obstacles;
- non recoverable slopes;
- presence of vulnerable users in border areas
- drainage structures and catchment boxes;
- gateways and support of plates and lamps;
- central sites with a history of accidents.
- works of medium or long duration.
However, it is vital that designers check out the location, the other risks involved and the traffic characteristics, as well as the accident history of the stretch.
What defines the level of risk on the highway
As a result of the need to install a guardrail in the road stretch in question, it is necessary to define the risk of this location, whether it is normal or high. According to NBR15486 of 2016, these risks are defined according to the following criteria:
Normal risk
- Accidents generated with normal severity, without additional consequences and dangers that can increase its severity and consequences.
High risk
Existence of hazards that increase the severity and consequences of an accident, such as:
- risk to third parties within the free zone, such as access to populated areas (school, housing or labor) along the road;
- structures that can collapse (footbridges, gateways and others);
- places that will lead to falls on high critical slopes;
- segments close to deep waters;
- areas of springs;
- sharp turns;
- sharp slopes;
- stretches with high accident rate;
- storage areas for chemicals and fuels;
- transmission towers.
Selection of road containment devices by containment levels
The selection of containment devices by level of containment must be made by homogeneous stretches of the highway. This allows each stretch to have an appropriate treatment of the site, optimizing the project costs. The selection of the containment device should follow figure 13 of the standard NBR 15486 of 2016.
Containment device selection factors
The selection of the containment device to be used in a roadway must be made according to the following factors:
- highway class;
- road speed;
- characteristics of the traffic, its volume and the percentage of heavy vehicles in circulation;
- physical characteristics of the road and its surroundings, adverse geometric conditions, as sharp turns and ramps, usually combined with low distance and conditions on the side of the road;
- consequences if a heavy vehicle penetrates or overruns the containment system in high risk locations;
- nature of the risk and obstacles on the road;
- accident statistics.
In this way, designer will be able to determine the level of containment that must be applied to this stretch of the highway, following the classifications:
- normal (N);
- high (H);
- and very high (VH).
For systems tested according to European standard EN 1317, we have the following:
- normal rating: N1 and N2;
- high rating: H1, H2 H3, L1, L2 and L3;
- very high rating: H4a, H4b L4a and L4b.
Other devices can be determined as temporary, rated T1, T2 and T3.
What guarantees the cost-benefit of a road safety project
The analysis of the risk level is fundamental to avoid unnecessary expenses in a road project. It is necessary to observe the different stretches of a highway and its specific characteristics in order to define the level of containment of the guardrail that will be installed there.
Usually, the marginal roads of lower classes, for example, have local traffic and lower speeds, where it is not necessary to resort to a higher level of containment. Other examples are maneuvering courtyards, parking lots and shopping malls. So, in the project, you can have ways to optimize cost, rather than applying high-level containment devices across the stretches.
It is possible to determine at each point in the project how it will be optimized correctly, without endangering the people who travel on that highway – and with the guarantees of the impact tests or crash tests.
The choice of longitudinal barriers should not be made solely based on guardrails prices, since a project following this criterion can endanger the lives of people traveling on those highways.
Projects must follow all the directives contained in NBR 15486 of 2016. We recommend the careful reading of this ABNT standard, which was designed based on European and American standards.
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Thank you very much,
Marcelo Raymundo
Commercial and marketing director