RECOMMENDATIONS FOR PLANNING
6.3.3 Traffic

Traffic Planning

Traffic planning measures such as the exclusion of through traffic from residential areas, bypass roads to relieve encumbered thoroughfares, speed limits, and support of public transit or of the bicycle and pedestrian traffic all contribute to the reduction of air pollution.

The connection between speed limits and emissions produced by vehicles is dealt with in Chapter 2.8.2.

Figure 6/31 emphasizes the criteria for traffic-calmed urban zones; namely, the bundled functioning of primary streets with bordering, shielding buildings and subterranean parking enclosures.

Since limitations of building use are to be expected in the vicinity of heavily-trafficked roads, the planning or the corresponding site plan establishment of roads with traffic counts higher than 10,000 vehicles/hour requires a report on the exhaust immissions level for the areas near the road. The tools available for immissions prognoses are explained in Chapter 4.3.3 to 4.3.6.

Evaluation of Exhaust Immissions Levels

For the evaluation of calculated pollution levels on roads and their nearby areas, the previous pollution levels as well as the intended uses in the vicinity of the road are important. In the case of a planning situation in an existing central-city traffic network, one may come to a different evaluation than in the case of a planning situation for a new residential area and roads – for instance in the course of a future local bypass.

Especially in the case of a new planning of residential areas, the precautionary values set by the WHO should be used for an evaluation (cf. Chapter 2.9). What needs to be considered at any rate during the weighting of the authorisation of residential uses – which are to be preserved or developed especially in special residential areas and welcome in core areas to revitalise the city – are the limit values defined within the 39th Federal Immission Control Ordinance with regard to the required planning measures.

In practice, a graded way of proceeding has often proved itself, i.e. that the exceeding of precautionary values leads to a planning reaction (a marking within the legally binding land-use plan plus an individual measure). Exceeded immission limit values from the 39th Federal Immission Control Ordinance (Ordinance on air quality standards and emission maximums) can still flow into the weighting process as serious air quality results in the context of development planning. This means that limit value exceedances in a planning area are possible in well-founded cases. But this must entail a presentation of possible measures to improve the situation (also outside the planning area). A decision in favour of a future residential use may be doubted under these conditions as the exceedance of limit values generally questions healthy living conditions in these areas for reasons of health protection.

Apart from that, clean air/action plans must always be established when limit values according to the 39th Federal Immission Control Ordinance are exceeded.

Immissions-Reducing Influences

The pollutant concentrations caused by traffic typically decrease strongly with increasing distance from a road. This reduction is also the case (with conditions) for nitrogen dioxide. Since the noise pollution from a road also decreases with distance, sensitive uses (e.g. residential, recreation, etc.) should be secured with corresponding protective distances so that both the noise protection requirements and the immissions criteria from the 39th BImSchG are maintained as minimum requirements.

In street canyons with buildings lining the road, there is no possibility for protective distances. Immissions protection mechanisms such as noise protection barriers and walls as well as dense plantings are quite effective remedies against exhaust pollution. Enclosed peripheral development produces a substantial reduction in pollution on the side of the buildings facing away from the street as well as in the area behind the buildings. As a rule, lower pollution levels are also present near the upper floors of peripheral buildings compared with the lower.

Vegetation as a means of immission control

The reduction of pollutants through trees and bushes results from the plants" mechanical filter effect (gravity separation), which is particularly effective for powdery or droplet pollutants, as well as from a modification of the wind field. Figure 6/32 depicts the recommended combination of deciduous trees and conifers.
However, recent studies show that, on sunny days with high temperatures, biogenic isoprene constitutes an important ozone precursor substance in urban areas. As stable high-pressure weather situations in summer must be expected more frequently in future due to the effects of global climate change, tree types which emit no isoprene should be preferred for new or replacement plantings.

The influence of plantings on the improvement of the immissions situation with pollutants on roads thereby distinguishes itself from the possibility of reducing sound levels with vegetation along roads (STAEDTEBAULICHE LAERMFIBEL, 2013).

Legal Bases (Pollution Control)

According to § 9 (1) 24. BauGB, a site plan can establish "protected areas to be kept free of development, areas for special facilities and precautions for protection from harmful environmental effects in the sense of the Federal Pollution Control Law, as well as for protection from such effects, or for avoidance or reduction of such effects from built and other technical precautions."

According to § 9 (5) 1. BauGB, areas should be denoted in a site plan whose development would require special built precautions against external effects.

Example of a regulation in accordance with § 9 (1) 24. BauGB:
"In the areas denoted with ‘IM", recreation areas for residences are only allowed if they are ventilated exclusively from the side of the building facing away from the street."

Another example regulation:
"MK3: Core area in accordance with § 7 BauNVO; residences are permitted above the fourth floor (§ 7 (2) 7. BauNVO)."

Notation:

If conflict management regarding design in individual planning processes can be carried out, it can be possible to denote areas whose development would require precautions against traffic noise and vehicle exhaust emissions in accordance with § 9 (5) BauGB.