Conclusions of the Cambridge meeting:

Conclusions of the Cambridge meeting

The results achieved by the TRAPOS teams show that traffic produced turbulence is a relevant factor for prediction of street level pollution

The data obtained during the URBCAP Nantes 99 campaign give an indication for additional turbulence in the lower part of the canyon and the existence of a vertical structure of the additional components

Furthermore the observed results indicate that an increase of traffic density leads to higher traffic produced turbulence components up to a threshold value after which higher traffic densities result in lower turbulence components

An analogy to this behaviour might be the phenomena of flow above roughness elements. In that case characteristic flow regimes can be defined depending on the distance between buildings (isolated roughness - wake interference - skimming flow) and the roughness parameters start also to decrease for building densities higher than a particular value.

It is more feasible to find parameterisations describing the spatially averaged effect of traffic (later called: traffic produced turbulence) in streets rather than for the effect of single cars (later called: car produced turbulence) .

A qualitative understanding of the phenomena and scaling concepts for the case of traffic produced turbulence exists.

The single-car case is less clear and has to be more analysed in the future.

In numerical models traffic produced turbulence should be taken into account by additional terms in the turbulent kinetic energy and momentum equations. So far it is not well understood if an additional term in the dissipation equation is necessary.

The concept for incorporating traffic produced turbulence in analytical operational models is clear and some particular details which have to be clarified were formulated.

The incorporation of traffic produced turbulence in numerical models used for regulatory purposes is not so clear at the moment. The definition of simplified methods similar to the so-called VDI-method, in which concentration forecasts are still based on normalised concentrations calculated without additional traffic produced turbulence formulations and TPT-effects are only taken into account by using a modified scaling velocity, seems rather difficult and physically not very grounded. It looks more feasible to define simplified traffic related terms which are directly implemented in the flow field and dispersion calculations, but the applicability of such approach still has to be tested.

Open questions:

Influence of street geometry

Situations with one-way traffic

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	The results achieved by the TRAPOS teams show that traffic produced turbulence is a relevant factor for prediction of street level pollution
	The data obtained during the URBCAP Nantes 99 campaign give an indication for additional turbulence in the lower part of the canyon and the existence of a vertical structure of the additional components
	Furthermore the observed results indicate that an increase of traffic density leads to higher traffic produced turbulence components up to a threshold value after which higher traffic densities result in lower turbulence components
	An analogy to this behaviour might be the phenomena of flow above roughness elements. In that case characteristic flow regimes can be defined depending on the distance between buildings (isolated roughness - wake interference - skimming flow) and the roughness parameters start also to decrease for building densities higher than a particular value.
	It is more feasible to find parameterisations describing the spatially averaged effect of traffic (later called: traffic produced turbulence) in streets rather than for the effect of single cars (later called: car produced turbulence) .
	A qualitative understanding of the phenomena and scaling concepts for the case of traffic produced turbulence exists.
	The single-car case is less clear and has to be more analysed in the future.
	In numerical models traffic produced turbulence should be taken into account by additional terms in the turbulent kinetic energy and momentum equations. So far it is not well understood if an additional term in the dissipation equation is necessary.
	The concept for incorporating traffic produced turbulence in analytical operational models is clear and some particular details which have to be clarified were formulated.
	The incorporation of traffic produced turbulence in numerical models used for regulatory purposes is not so clear at the moment. The definition of simplified methods similar to the so-called VDI-method, in which concentration forecasts are still based on normalised concentrations calculated without additional traffic produced turbulence formulations and TPT-effects are only taken into account by using a modified scaling velocity, seems rather difficult and physically not very grounded. It looks more feasible to define simplified traffic related terms which are directly implemented in the flow field and dispersion calculations, but the applicability of such approach still has to be tested.