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Three-dimensional geometry of roadways (VSS1998/083)

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Background & Policy context

The study of road projects and traffic facilities in general has always been carried out according to a perfectly defined cutting out. This cutting out gives rise to the successive study of the three aspects of the plan: plan view, longitudinal profile and cross-profile. These three notions, strictly connected are of easy access; it becomes more difficult when one wants to handle them simultaneously.

It is nevertheless essential to have a global overview on specific problems that cannot be processed by the successive study of three traditional plans. Visibility, as well as the integration in the landscape for example, is typical aspect characterized by the integration of the three dimensions (plan view, longitudinal and cross profile). They are on top of the fundamental characteristics of any road plan. Viability, safety and quality of a plan will depend on it. It is therefore essential to master perfectly these questions.


The main goals of the project are as follows:

  • To assess method and basic principles allowing to draw a plan based on a global and spatial approach, and by taking into account its integration in the landscape.
  • To define the needs and fix the rules for a global study of sectors with sensitive geometry.
  • To develop elements for the revision of the standards dealing with road plan (VSS SK 173.1), and projects (VSS SK 173.8)


Parent Programmes
Institution Type
Public institution
Institution Name
Swiss Government: State Secretariat for Education and Research
Type of funding
Public (national/regional/local)


Road design has always been done according to a perfectly defined procedure, in which the three main elements of the alignment are considered successively, the horizontal alignment, the longitudinal profile and the cross profile.

Taken individually, these three elements depending on each other are easily accessible. The problem becomes more difficult if they are to be handled simultaneously. Nevertheless, a global view in three dimensions is necessary for certain parameters of the alignment like visibility, legibility or its integration into the landscape. These are fundamental characteristics of which depends the road safety, viability, as well as the general quality of the road. The control of the interactivity between the different plans is thus essential. 

The appearance and the development of computer aided design (CAD) software has allowed to partially meet the needs of three dimensional treatment, particularly on the level of project visualization, being an important communication tool between professionals and the public. However, some lacks still remain. 

The present research work allows the prospecting and a theoretical analysis of methods and basic principles allowing a better spatial control of the alignment. Without completely revolutionizing road design, it leads to some specifications for road CAD software allowing not only a better design, but also a better control of the road network, for example during road safety audits.

The basic conclusion of the project is stated as follows:

The problem of the design of taxiways was complicated with the need to take into account new constraints environmental and social policies and the need for greater speed treatment.

The development of the design using computer tools allowed to meet some of those needs. They allow a saving of time and increasing of productivity and a three-dimensional visualization of projects, tremendous tool communication with professionals and the public.

However some gaps remain because of the processes which are based on software which  is identical to that previously used during manual design. Processing times are shorter, but the form is remained the same, namely a classical design methodology by plan-areas.

The aspects that were not previously treated or poorly are always with result in non-optimal paths designed with respect to certain aspects. Ideally, the geometric design of roads should be directly

in three dimensions, from three-dimensiona


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