Changes in road safety regulations may arise doubts among designers about how to proceed to achieve the new performance concept in metal fenders. Also known as guard rails, metal longitudinal containment barriers are designed to redirect the vehicle and minimize the impact in automobile accidents, reducing the risks to the driver and passengers.
The lack of knowledge about the rules regarding metal defenses can be a major obstacle for the designers, especially when those responsible for examining road safety projects are unaware of the specifications. At this point, it is necessary to prove that all legal guidelines were followed in the design.
In order to avoid that the insecurity on road projects is an obstacle for the designers, we will present the main points of the norm NBR15486 in this article.
What is the NBR15486 standard
NBR15486 is the standard for traffic safety that establishes the road restraint device design guidelines and determines the impact testing requirements.
Historically, the road safety market was mainly normalized by NBR9670 and NBR9671, which did not include levels of containment, since these documents established how to manufacture metal defenses, describing materials and dimensions to be followed. There was also the NBR15486/2007 standard, which presented many gaps in the containment levels concept.
Until the revision publication of the NBR15486 standard in March 2016, metal fenders manufactured in accordance with NBR9670 and NBR9671 standards that did not have containment levels because they were not tested in laboratories. The models followed what had being done in the international market since the 1970s.
However, since March 2016, with the NBR15486 standard, all new road safety projects must, necessarily, follow the containment levels guidelines.
Road design guidelines
The NBR15486 standard is responsible for establishing guidelines for road restraint devices in Brazil. It includes the aspects to be considered to guarantee the performance of devices and containment barriers, such as metal fenders and terminals, among others.
The first important point is to determine the risks involved in the stretch of the highway and, in order to do so, the following aspects should be analyzed:
- Free zone calculation;
- Presence of fixed obstacles, drainage structures, critical slopes and vulnerable users – all within the free zone;
- Central beds;
- Medium or long-term works on site.
After this analysis, we can verify the need – or not – to protect the site if risks can not be eliminated such as repositioning a fixed obstacle outside the free zone.
If the protective barrier is imperative, we need to know if we are facing a high or normal risk. We consider high risk when there are situations that aggravate the consequences of this accident, such as the presence of:
- schools;
- houses;
- collapsible structures such as walkways and porches;
- critical slopes with risk of vehicle falling;
- segments presenting a risk of drowning;
- areas of springs;
- sharp curves or slopes;
- fuel or chemical storage locations and high voltage towers.
We consider normal risk when the accident does not involve additional consequences or hazards that may aggravate the consequences of an accident.
The second important point is to determine the conditions of the place and its type of traffic. For this, we analyze:
- the class of the highway;
- the speed of the stretch;
- the road VDM (average daily vehicle);
- the percentage of heavy vehicles;
- the track geometry.
With this information, you can use the contention device selection diagram – shown in Figure 13 of the NBR15486 2016 standard – by following the 6 steps of this schema.
This way, the designer will be able to determine the level of containment that must be applied to this section of the highway, following the classifications:
- normal (N);
- high (A);
- and very high (MA).
For containment systems classified according to EN 1317 European standards, we have the following:
- Normal classification: N1 and N2;
- High classification: H1, H2 H3, L1, L2 and L3;
- Very high classification: H4a, H4b L4a and L4b.
Other devices can be classified as temporary, T1, T2 and T3 classification.
It is important to note that to determine the containment level of a device, it is mandatory that the system manufacturer performs the actual Crash Test in a credited laboratory.
Next, it is imperative that the work zone and the safety of passengers are analyzed by severity when the car hits the containment barrier (ASI and THIV).
This standard also includes the recommendations that projects must contain:
- specifications of the containment device and workspace;
- schematic drawings, including track clearance, required length, lateral slope and terrain effects;
- the lateral clearance of the containment device relative to the edge line of the track and also the distance from the fixed obstacle – not less than the work area or the minimum distance of 0.5 m behind the device when installed in slopes.
Other important points of the project are:
- effects of the terrain at impact, where the wheels of the vehicle must be on the ground and the suspension can not be compressed or extended at that time
- lateral deflection gradually, obeying the 1:10 ratio – or being softer than it. It is also essential to analyze the lateral deflection table, because of the speed, for rigid and semi-rigid systems such as New Jersey;
- fixed minimum obstacle lengths, where an angle of 15 degrees is established between the edge of the track and the outer face in that obstruction.
This standard also contains:
- Testing matrices on European and American standards;
- tables on severity of impact, workspace and intrusion;
- calculation of free zone with tables, drawings and abacuses;
- slope and drainage information;
- basic guidelines for plate and light fixtures;
- impact terminals;
- Impact attenuator devices;
- containment devices in the work area.
Other road standards
The national regulations followed regulations applied in other locations around the world, mainly the EN1317, used in the European market, and the MASH, applied in the United States. In addition, it is worth checking also the standards of metallic defense NBR 6970 and 6971 and the standard of rigid barriers.
To meet all legal requirements for road projects, designers must be aware of what is set forth in NBR15486 standard. This content sought to elucidate the main points on the subject, but it is imperative to acquire and read this directive carefully, because its complexity and importance are high.
If any doubt persists, use the space for comments and leave your comment. Share your experience in the road security projects deployment and in the application of metallic defenses!
Thank you,
Marcelo Raymundo
Commercial and Marketing Director