| 4. |
Methods of Information Acquisition
for Planning (Nature measurements, Wind tunnels, Modelling) |
||
|
|||
.
|
4.2.4 Example
Use – Small-Scale Dispersal (Tunnel Ventilation) Scenario 4.2.4.1 Problem Definition In the context of transportation planning involving new roads or new traffic densities on existing routes, the issue of measures to reduce exhaust and noise pollution arises repeatedly in densely-settled cities. Although sufficient calculation procedures already exist for the determination of noise pollution, there are no complex useable models to calculate exhaust gas dispersal on roads and tunnel portals in topographically-varied areas with existing development and vegetation (s ee also Chapter. 4.3).In the present case, therefore, it was necessary to rely on the simulation of the local situation in a wind tunnel. . Planning Concept and Tasks From a large-scale perspective, a planning scenario arose as a result of the new construction of a federal highway (B312) coming from Fellbach that was intended to connect to the existing B10 highway in the Neckar valley. Since a concurrent goal was the relief of traffic in eastern Stuttgart (Wagenburgstrasse), it was necessary to direct traffic in the direction of the central city via the B10 to the B14. This large-scale situation is depicted in its initial state in Figure 4/17 and in its planned state (now completed) in Figure 4/18. In the Stuttgart neighborhood of Berg, the road layouts for the B10 and B14 were newly conceptualized to account for the desired traffic redirection. Problems arose, however, when it was realized that this traffic plan would have an immediate effect on two outdoor swimming pools (Figure 4/19), a park, and a residential area. . Planning Structure and Content Thus it was planned to connect the Federal highways B10 and B14 in the Berg neighborhood through the Berger Tunnel II (Figure 4/19). The tunnel was to begin in the area of the east portal of the existing Schwanenplatz Tunnel and end on the B10 in the area of the "Berger Steg" bridge over the Neckar River. The already-existing "Leuze Tunnel" could then lead into the planned "Berger Tunnel II" south of the Leuze swimming pool. No dedicated ventilation systems were planned for the stretches of tunnel. Exhaust was intended to simply exit from the tunnel portals. The largest changes in the traffic densities arose in the southern section of the B10 through a doubling in traffic counts from ca. 43,000 to ca. 87,000 automobiles per day. In light of this, however, exhaust discharges were installed near the residential area south of the Schwanenplatz Tunnel. . Climatic and Air-Hygienic Problems in the Planning Concept Air pollution levels in the study area were already high at the time the new traffic concept was planned. According to measurements by the State Institute for Environmental Protection, NO2 levels on the land that was supposed to contain the three stretches of tunnel stood at 75% of the threshold value according to TA Luft (1986); furthermore, the 98-percentile value reached 100% of the threshold value. Neighboring areas showed similarly high levels of pollution. According to the Stuttgart Emissions Register at that time, more than 90% of NOx emissions in the area under consideration and its surroundings originated from traffic. The planned construction would increase traffic counts in the affected area, so that an overall increase in total emissions was to be expected – in spite of anticipated improvements in automobile emissions systems (e.g. catalytic converters). Exhaust gas from the existing tunnel stretches was to originally have been blown out horizontally. This is unfavorable for the pollutant concentrations in the vicinity of the tunnel portals because the pollutants are collected in the tunnels and then released in high concentrations at the portals. Higher pollution levels are to be expected near the portals, above all in relation to short-time values, in comparison with exhaust release over an open stretch of road or in a tunnel with slits in its roof. One of the potential advantages of tunnels, namely the controlled collection of exhaust within a tunnel section, can be turned into the exact opposite through inadequate removal of exhaust gases at the tunnel portals. |
| . | |
| . .
|
|
|
||||||||||||||
| . | ||||||||||||||
|
