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In order to increase
the attractiveness of public transport (and cycling) and the quality of life of
those citizens living at the before mentioned streets, the objective needs to
be a (partial) displacement of individual motorised vehicles. A system of ring
roads and tangent streets appears to be the most efficient solution. A good
traffic infrastructure for such cities is a ring road system: an inner city
ring to surround car-free city centre, medium ring road through less sensitive
town quarters with a city-limit maximum speed and without single-level
intersections, thus an higher attractiveness for vehicles than the radial
roads, partly usage of existing roads recommended, outer city ring with high
speed roads for traffic not aiming for the city itself, in addition: tangent
roads.
The radial roads can at
the same time be narrowed to allow more urban life quality.
This way, the following
results can be achieved:
·
Public transport
becomes more time-reliable, fast, better as it is no longer hindered by traffic
congestion (supported if possible by the development of an urban railway
network),
·
Individual motorised
traffic is edged out of the radials but remains attractive enough in order to
avoid traffic sneaking through residential areas,
·
Commercial traffic is
not hindered,
·
Air quality of densely
populated quarters is getting improved.
More radical measures
to displace or decrease the individual motorised traffic can’t usually be as
effective as the public appreciation of the problems is lacking.
Also such a strategy
appears promising and is, for example, promoted by the City of Leipzig; the success of this approach depends also on the
demographic development of the concerned city. Usually additional complementary
measures are necessary to achieve the intended results.
Specific
infrastructures providing benefits from the environmental point of view are
tunnels and roundabouts
Tunnels
The use of tunnels in
urban contexts allows the separation of long distance and local flows; the
first ones moves in the tunnels with higher speed by leaving free capacity on
the local road networks. Relevant benefits may be obtained for the reduction of
gaseous and noise emissions of the streams running inside the tunnels and for
the better circulation regimes created outside the tunnels by the flows
separation.
Environmental
disadvantages of such infrastructures are due: a) to the high concentrations of
pollutants around the tunnels mouths and inside the tunnels themselves (walking
or cycling paths inside the tunnels should be avoided), b) to the critical
safety condition in case of fire inside the tunnel, c) to the need of spaces
for the entering and exiting sloping links.
Roundabouts
The use of roundabouts in urban
contexts allows the increase of the mean speed of flows thanks to the
minimisation of stops at the intersections (stops and traffic lights are
minimised), which may be concentrated in the roundabouts. Relevant benefits may
be obtained for the reduction of gaseous and noise emissions for the better
circulation regimes created by the intersection organisation. Environmental
disadvantages of such infrastructures are mainly due to the relevant need of
spaces required by the roundabouts geometry. |