Suburban motorways are part of the local road network and are therefore congested during peak-hours. Increasing road capacity causes traffic to shift to new routes and times of day. Increased road capacity also leads to increased use of the automobile instead of public transport. Therefore, the problem of congestion (including slow-moving traffic) is not resolved by increasing road capacity. Experience shows, that even when new roads initially reduce congestion-time, a short time later, the former levels of congestion are reached.
In light of these facts, it was concluded that the purpose of suburban motorways is to channel traffic in order for the local road-network to function smoothly, optimised for local needs, keeping the negative aspects of road traffic such as noise, air pollution, and accidents away from residential areas. Therefore the travel time between two points must be shorter by way of the suburban motorway than by travelling over the local road network. Depending on local conditions
speed-limits between 50 and 80 km / h may be enough. Overall road-capacity and safety have priority over higher speed.
When congestion on the suburban road network (motorways and other arterial roadways) is unavoidable, it is necessary to see that a common traffic regulatory system be established. Through coordinated efforts residential neighbourhoods, public transit, and traffic flow outside the congestion area, should be protected from the negative impacts of congestion. The question and main objective of this project arises: how to deal with the congestion issue.
Measures for elimination of congestions were defined as follows:
Motorway access and exit ramps are especially prone to congestion. Often the local road network cannot accommodate the additional traffic coming from the motorways; or the incessant traffic flow from the local network causes congestion on the motorway. In order to limit the unavoidable congestion on the motorway access ramps, we need buffer areas in the immediate vicinity of the ramps to contain it. It can be necessary in these cases, for lack of a better alternative, to employ the use of the emergency lanes as a way to enlarge access ramp space.
A more far-reaching measure is to entirely incorporate the emergency lane into the traffic scheme in order to avoid congestion and its accompanying dangers. This requires a reduction of the speed limit and may also require a ban on overtaking for lorries. Additionally, emergency stopping areas must be specified, taking into account the maintenance required. With speed-limits lowered to 80 km/h the minimum dimensions for the road layout such as horizontal or vertical radii can be reduced to less than half of those used for a standard motorway. A more flexible layout is possible.
When a denser intertwining with the local road-network renders even this standard impossible or not useful, then the standard of an urban main road comes into use. Here it is possible to regulate the interchange with a traffic light and thus coordinate the timing closely with the overall urban traffic regulation system. At a maximum speed limit of 50 km/h the minimal radial roadway dimensions can again be reduced by one third compared to those for 80 km/h.