Methodological proposals for improved assessments of the impact of traffic noise upon human health

Several methodological shortcomings still hinder the inclusion of transport noise as an established impact category within life cycle assessment (LCA). Earlier attempts to quantify the health damages caused by traffic noise yielded valuable results from an academic point of view, but these were of limited use in the context of everyday LCA practice. An enhanced understanding of traffic noise emission models coupled with a straightforward choice of indicators could lead to faster, more accurate assessments of health impairment due to traffic noise whose results would fittingly serve the purposes of policy makers and the information needs of the general public alike. This article aims to propose the guidelines for such assessments.

The assessment method presented takes an incremental approach in similar fashion as previous work in the field done by R. Müller-Wenk. An explanation is provided of how the assumption of linearity leads to a substantial overestimation of noise level increments attributable to additional vehicles, and subsequently to a misjudgement of overall health impacts due to traffic noise. Hence, an alternative calculation method allowing for better accuracy in the computation of noise level increments is proposed. This method can be easily applied, needless of a specific traffic noise emission model. A more detailed method, based on the state-of-the-art Improved Methods for the Assessment of the Generic Impact of Noise in the Environment (IMAGINE) traffic noise emission model, is also described. This method is to be applied to large-, medium- and small-scale assessments where variations in traffic flow or composition can be reasonably predicted or measured. In the proposed methodology, health impairment due to traffic noise is not aggregated in DALY (disability-adjusted life years). Rather, the results are given in terms of the ‘number of annoyed persons’, which is derived from the synthesis curves relating noise exposure to annoyance presented by Miedema and Oudshoorn. The calculation procedure and data needs to do this are explained. Moreover, the validity of taking the number of annoyed persons as a proxy for overall health impairment due to traffic noise—and the main benefits of doing so—are discussed. Performing the attribution of impacts on a per vehicle-kilometre basis can lead to impact misrepresentations whenever an incremental approach is taken. A different attribution scheme, which takes background noise into account, is thus proposed.

The general framework of a method to assess the impact of traffic noise upon human health within LCA is presented. This method, which finds its basis in the work of Müller-Wenk, can be used to evaluate a large number of variations in traffic other than mere increases in overall traffic flows. An application example evaluating the impact of a generic 1,000-km trip of a heavy-duty vehicle through Spain is provided in Section 2.4.

The incremental approach seems most adequate for the assessment of the impact of traffic noise upon human health within LCA, albeit the assumption of linearity can significantly distort its results. Likewise, performing the attribution of impacts through generic characterisations of additional vehicle-kilometres may mask the true responsibility of traffic for increasing noise levels, and is therefore advised against. The special characteristics of noise as a pollutant (relevance of spatial data, human perception issues) appear to justify the adoption of a distinct indicator, namely ‘number of annoyed persons’.

Reasonably good estimates of equivalent noise level increases due to proportional increases over pre-existing traffic can be given without using a noise emission model. Yet, the use of state-of-the-art vehicle noise emission models (e.g. IMAGINE) should allow for more accurate assessments, provided sufficient data regarding the spatial distribution of receivers and traffic characteristics (traffic flow, average speed per vehicle type and so forth) are known. Incorporating annoyance as the preferred indicator for the impact of traffic noise upon human health would make assessment results more intelligible and readily applicable to decision making in matters like infrastructure policing and urban planning, whilst placing the focus on damage prevention.

In this paper, only road traffic noise is dealt with. However, annoyance curves with a comparably solid scientific background also exist for railway and aircraft noise, which would make comparisons between alternative transportation modes feasible. The use of ‘number of annoyed persons’ instead of DALY units is favoured because it allows for a more straightforward presentation of results, even if it excludes the possibility of aggregation with other health impacts. Nevertheless, the use of DALY is not excluded beforehand, insofar as a scientifically sound relationship between long-term exposure to environmental noise and more severe health conditions is agreed upon by medical experts.