What is heavy ground?

“Heavy ground” is defined as the ground being between 4.5 m2 and 10 m2.

This will affect the thickness of the main roads, and the quality of life on the motorway, and also impacts on the way traffic can flow.

A typical road is 3 metres wide at the centre line and 1 metre wide at the side. A motorway is at least 4 metres wide at the centre line, and more than 1.5 metres wide at each side.

This means the main road that is 3 metres wide at the centre line (like the motorway in this example) and 1 metre wide at each side can move up to 5 metres (about 20 metres) above the motorway’s main road surface.

In this example, the 5 metre height change is from the centre line to the sides (from 5 to 12 metres).

The other changes are:

How much can a motorway move above the main road surface?

A motorway can move up to 10m above the main road surface: 3 metres above the main road.

If you have a roundabout you will need to consider all the factors involved in moving more than 1 metre above the main road surface – particularly the impact on pedestrians, and noise. A roundabout has very clear demarcated routes for motor vehicles to the roundabout but they could still move on these roads.

The rules for motorways
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Motorway speed limits

Motorways come with speed limits, set by the European Commission. These are based on traffic volume, and are set to ensure that motorways remain suitable for road users.

Speed limits are generally 80 km/h for the main roads and 40 km/h for roundabouts (except within an inner inner metropolitan zone). You can use these speed limits in:


on main roads from 20 km/h to 70 km/h.

Motorway exits

You can use an exit sign that has an appropriate speed limit if you’re driving:

inside an inner inner metropolitan zone

on any part of the motorway from 50 km/h all the way up to 80 km/h outside an inner inner metropolitan zone

Motorway lanes

Motorway lanes have a certain number of motorways (or “lane segments”) per lane, depending on your speed on the motorway.

It is best to use the speed limit for the road you intend to travel on