"Every NABO has its own story."

The Netherlands ranks among the world leaders when it comes to the safety of level crossings. Yet things still regularly (almost) go wrong at Non-Actively Secured Level Crossings (NABOs). ProRail is therefore pressing ahead with closing or converting these unguarded level crossings. Engineering and consultancy firm Antea Group now has twenty NABO locations in preparation. 

The Not Actively Secured Level Crossing: you find it mostly in the countryside; in places where local and private roads cross the railroad tracks. Often equipped with an Andreas cross, but not secured with barriers, bells and light signals. Crossings where you have to be incredibly alert as a road user, knows project leader Björn Heijmer of Antea Group. "People mistake the speed at which a train races by, visibility is often poor." This regularly creates life-threatening situations; an average of two fatal accidents occur on NABOs every year. 

The NABO program

The Ministry of Infrastructure and Water Management (I&W) therefore instructed ProRail to close 180 publicly accessible NABOs as soon as possible. In 2019, ProRail closed 25 NABOs. For 120 other level crossings, ProRail called into being the NABO program. This aims to close a large number of NABOs within five years: for 50 level crossings there will be an alternative. To this end, ProRail developed four possible solutions: a stairway over the tracks, an underpass, a new access road or a U-bay (which uses an existing bridge or viaduct). 

Antea Group was selected by ProRail to create a design for fifty NABO locations, to draw up the tender dossier and to supervise execution. "We now have about twenty NABOs under consideration: most of them consist of underpasses, stairs and access roads," says Heijmer. This means that ProRail has engaged with stakeholders in the exploration phase to choose the best alternative. "After that, we come into the picture. We conduct conditioning studies, enter into discussions with parties about the design details and create a principle design. Then we prepare the tender dossier." 

Fitting and measuring

Every NABO process is one of fits and starts. Heijmer: "A solution touches local and private interests. Pedestrians, cyclists, farmers and recreationists: you want to arrive at an appropriate solution for everyone." This sometimes results in interesting conversations. "For example, in Almen we are working on a NABO over which an equestrian trail runs. The owner of the riding school wants to preserve this path. We are therefore designing an underpass that allows a rider, with his horse in hand, to pass safely. This means that the design must take into account the behavior of a horse. An underpass that later no horse wants to pass through is obviously not an option."

In addition, a variety of environmental factors affect the solution. Heijmer: "In Oisterwijk, we are closing a NABO over which a footpath runs. We found a wonderful solution by constructing a U-bay under a bridge further on. But to take the path there, we have to lay it partly through a Natura 2000 area. For this you have to sit down with the Water Board and Brabants landschap to examine how you can still get this done within all the frameworks."

Parametric designing

This is where the big challenge lies. "Every NABO has its own story and requires a unique design. At the same time, you strive for a standard approach that allows you to bring each project to completion efficiently." To maintain that speed, Antea Group uses parametric design, among other things. Heijmer: "This allows us to quickly work out various alternatives for each design. For example, we are working on an underpass in which we are working with stairs: what effect does a certain stair slope have on the space requirements or the number of cubic meters of concrete? Thanks to parametric design, you can "play" with design parameters. Each variable you adjust is automatically converted to a new variant. You get through the design process faster and arrive at better solutions."

A year and a half after the program began, one NABO alternative has been realized (De Kers near Haaren: a new access road). Heijmer expects several projects to come to fruition in the coming months. "You notice that a lot of time and energy goes into the preparation. After all, you can only do it right once. The fact that we now have a third of all NABOs in preparation means that we have taken a big step towards greater safety along the railroad tracks."