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Environmental impact of traffic

Environmental impact of traffic

Road traffic forms the most important source of noise and air pollutant emissions in urban as well as rural environments. Research within the acoustics group of INTEC on the environmental impact of road traffic is mainly focused on measuring and modeling emissions and immissions.

Traffic modelling and time-dependent prediction of noise and air pollutant emissions

A dynamic prediction model for noise has been implemented at the INTEC's acoustics group, called MicroBASS. Noise in urban environments is mostly evaluated by the calculation of noise maps, using a set of standard calculation schemes for the evaluation of the contribution of different sources. Mostly only average noise levels (typical LAeq or Lden) are mapped. The MicroBASS model makes it possible to draw time-varying maps of the noise level, and by consequence, maps of derived measures, such as L10 or L50 (the noise level which is exceeded 10% or 50% of the time). It is even possible to draw maps of totally new indicators, which are based on the time evolution of the noise level. In the following sections, the basic building blocks of the model are described. Recently, MicroBASS has been extended with a module that predicts air pollutant emissions, such as carbon monoxide and particulate matter.

Time-varying traffic simulation
Predicting the dynamics of urban emissiones requires a model for road traffic that can account for time-varying traffic flows. A traffic simulation model based on cellular automata, shortly called a micromodel, is used for this purpose: Paramics, a commercial software package. In such a computer model, each individual vehicle is modelled as an object with its own properties and behaviour. It is possible to simulate large networks, such as a part of a town; also various traffic management facilities such as traffic lights, roundabouts and speed bumps can be modelled. Paramics allows users to extend its simulation model by the use of plugin dll's, written in C++.

 

 

Single-vehicle noise and air pollutant emission
Noise and air pollutant emision extensions to this micromodel were developed, which simulate the time-varying emissions caused by each vehicle. For the noise emission extension, the European standardized Harmonoise emission model was implemented. This model associates several noise sources with each vehicle, which roughly correspond with the noise sources of actual vehicles, such as the noise produced by the contact of the tires with the road, aerodynamical noise and the propulsion noise, produced by the engine and exhaust pipe. Each noise source consists of a spectrum in 1/3-octave bands, and the level depends on the speed and acceleration of the vehicle, as well as of the vehicle type. Characteristics of the road the vehicle is travelling on, such as the surface type, temperature and age, have also their influence. For the air pollutant extension, the VERSIT+ emission model, developed at TNO is used (Enviver).

Sound propagation
Because of the local character of sound, it is more useful to consider the immission levels at the location of a potential listener, instead of only considering the emission, as we usually do for air pollutants. To know the sound level at the observer and to be able to make maps of noise levels, possibly varying in time, one has to know the path the sound follows from its source. For this, a state of the art noise propagation model, developed at our research group, was used, which is based on object precise polygonal beamtracing in 2.5 dimensions. We refer to the noise mapping section for this. At the right, you can see a snapshot of a dynamic noisemap, simulating a single vehicle driving in an urban environment. 

Some relevant references

 

 

Measurement networks

IDEA