Verklaring betreffende de aanleg van internationale hoofdverkeerswegen

1. The fundamental characteristics of the design and construction of the main international traffic arteries, hereinafter designated as “international roads”, are dealt with in the following provisions. They apply only to the sections of these roads outside built-up areas. The latter should be by-passed if they constitute a hindrance or danger.
2. It is always desirable to adopt maximum dimensional characteristics whenever this is possible without undue expenditure; those indicated hereinafter as a rule represent the minimum. However, in some exceptional cases (unfrequented roads, mountainous areas, very difficult terrain, etc.), reduced dimensional characteristics adapted to local conditions may be allowed, subject to the fullest possible observance of the spirit of the directions given below, and in particular of those relating to homogeneity of alignment.
3. The roads are built according to the volume and the composition of the traffic to be accommodated and with reference to a suitably selected design speed. The volume and composition of traffic to be considered are those of some definite peak hour, excluding peaks occurring with low frequency, so as to limit the hours of congestion to an acceptable number with due regard to the probable development of traffic. The design speed chosen is as high as possible with due regard to the importance of the road, the topography of the region traversed, and other local conditions.

International roads are classified into the following categories:
A. Ordinary type roads
(a) Category I: Roads having a single carriageway with two traffic lanes each at least 3.50 metres wide
These roads can normally accommodate volumes not in excess of 600 vehicles/hour with 30 per cent heavy vehicles or 900 vehicles/ hour without heavy vehicles, provided the geometric characteristics of the road ensure good passing sight distance on the greater part of the length of the road and crossings at grade are not too numerous.
(b) Category II: Roads having more than two traffic lanes each at least 3.50 metres wide
Under the same conditions as above these roads can normally accommodate volumes not in excess of 900-1300 vehicles/hour for 3-lane roads. Four-lane roads can accommodate 1500-3000 vehicles /hour according as the percentage of heavy vehicles is high or low and the traffic in the two directions even or uneven. It is also recommended that, for greater safety, separate one-way carriageways be provided whenever possible where the intensity of traffic exceeds 600-900 vehicles/hour. In the case of 3-lane roads, longitudinal marking is especially necessary.
B. Motorways
Motorways are roads for automobile traffic only; they are accessible only from specially designed interchanges and have no crossings at grade. These roads generally have two separate and independent one-way carriageways each carriageway having at least two traffic lanes each with a minimum width of 3.5 metres.

(a). Cross-section
1. Shoulders In addition to the carriageways, international roads are provided with shoulders at least 2.5 metres wide. Clear lateral areas free from any obstacle are provided over at least 1 metre from the edge of the carriageway.
2. Special paths Special paths for the exclusive use of pedestrians or cyclists are also provided on the shoulders of ordinary type roads whenever a daily volume of 500 pedestrians or cyclists (or road-users of a similar category) is reached.
3. Trams and railways Trams and railways are excluded from the carriageway o± ordinary type roads and from within the formation of motorways.
4. Crossfall On straight sections the cross-section of the carriageway consists of one or two planes with as small a crossfall as possible and 3 per cent maximum. The minimum radius below which bends must be raised is 1000 metres. The maximum superelevation is 8 per cent.
5. Extra width on curves Extra width is provided on curves to ensure the free passage of the largest authorised vehicles when meeting.
(b). Horizontal and vertical alignment
1. Homogeneity of alignment International roads present homogeneous characteristics over sufficiently long sections. Changes in characteristics are made at points where they are normally obvious to a driver (such as passing through a built-up area or a change in topography). If this is not possible they are introduced progressively.
2. Geometric characteristics The principal geometric characteristics of the international roads are summarized in the following table. (1) The minimum radii of convex vertical curves given in the table relate to approach gradients which are approximately equal and of contrary sense, the difference in slopes being moreover sufficient to limit the visibility. The design speed of 120 kms/hour is only chosen if the carriageways are separated and if most of the accesses are specially designed. The figures (given for the radii of convex vertical curves are absolute minima. They ensure, for the given design speed, strictly sufficient visibility distances under normal traffic conditions and in the absence of unfavourable factors (such as smooth tyres or wet roads). Concave curves are such that, for the given design speed, acceleration may not exceed 0.50 m/sec2. The figures for the radii of horizontal curves are the minimum needed to ensure the stability of the vehicle. They should be increased by at least 50 per cent for easy and comfortable travel. The curved and straight sections of the horizontal alignment are connected by gradual bends. The horizontal and vertical visibilities provided are such as to give the same degree of safety, taking gradients into account, if any. It is often possible to achieve a favourable solution by doubling the carriageway at summits and bends. On two-way carriageways with 2 or 3 lanes the necessary passing sight distance is ensured on a percentage of the total length of the road as high as possible and distributed with the utmoss uniformity. This percentage must be at least 50 for the traffic volumes mentioned in chapter II for the ordinary type roads of category I and for the 3-lane roads of category II.
(1) The minimum radii of convex vertical curves given in the table relate to approach gradients which are approximately equal and of contrary sense, the difference in slopes being moreover sufficient to limit the visibility.
(c). Special measures
1. Stopping and parking Stopping and parking are prohibited on motorways. The shoulders of these roads are shaped with a minimum width of 2.5 metres to permit vehicles to stop in an emergency. In order to reduce the stopping and parking of vehicles on the carriageways of ordinary type roads carrying average daily volumes in excess of 1500 vehicles the following should be provided off the carriageway: (a) lay-bys; their spacing is governed by local factors such as the number of adjoining properties and the volume of traffic;
(b) draw-ins for buses.
(a) lay-bys; their spacing is governed by local factors such as the number of adjoining properties and the volume of traffic;
(b) draw-ins for buses.
2. Lighting The lighting provided on sections carrying important night traffic is uniform and sufficient to enable motorized traffic to travel without headlights.

1. Elimination of secondary intersections
The crossing at grade of ordinary type international roads by local roads of secondary importance is avoided as far as possible.
2. Intersections and interchanges
The intersections on an international road should be specially designed for the traffic using them.
Such designs include:
(a) for motorways roads at different levels with a connected system of entrances and exits avoiding any traffic cut on the motorway. The system of connecting roads includes, where necessary, acceleration and deceleration lanes distinguishable from the carriageway of the motorway and of sufficient length to enable drivers to execute the required manoeuvre and to change the speed of their vehicles to get from one road to another without interfering with traffic on the motorway.
(b) for ordinary type roads arrangements for crossing and for connection according to the principles given in (a ) above when the traffic flows are of sufficient importance. If a grade-separated intersection is not justified directional islands are provided to canalise the traffic crossing on the secondary road. If necessary, the carriageway of the international road should be duplicated to provide an adequate waiting zone for vehicles between the opposing directions of travel. The mutual visibility between roads entering an intersection is sufficient to permit a safe approach and crossing of the intersection. The intersection is designed so as to reduce, as may be necessary, the speed of vehicles coming from the side road, account being taken in particular of the visibility. Acceleration and deceleration lanes contiguous with the carriageway of the international road are provided at important intersections particularly when there are dual carriageways.
Roundabouts and light signals should in general be avoided.
3. Access to adjoining property
Direct access of adjoining property is not allowed on motorways. For ordinary type roads it would be desirable for laws to be passed to permit the limitation and control of access to adjoining property,
4. Railway level-crossings
Railway level-crossings should not be used on international roads.

1. Alignment and cross-sections: No modification of the characteristics of the carriageway and, if appropriate, of cycle-tracks or footpaths is allowed over and under structures. The clear margins are retained.
2. Overhead clearance: The minimum overhead clearance for new or rebuilt structures is 4.5 metres.

1. Road design should ensure the harmony of the curves in vertical and horizontal alignment.
2. Roadside hoardings should be prohibited.