Social benefit calculations of reduced noise from electric bus transport in Gothenburg
In this study we examine noise from different types of buses. The aim is to calculate the economic benefits of electric buses over other bus types used in Gothenburg in terms of noise reduction. Since there is no established method to investigate the economic effects of noise from buses a large part of this study focuses on if methods currently available to quantify the health effects and economic costs of noise are sufficient to assess the effects of noise from buses. DALYs is a measure that has been developed by the World Health Organization (WHO) to quantify the health effects by counting the number of healthy life years lost every year because of the noise. ASEK is a Swedish method used to calculate the costs caused by the transport sector to society every year.
In order to calculate noise from buses in a sufficiently correct way, it is necessary to have knowledge on how the different bus types operating in Gothenburg today sound. In Gothenburg there are diesel, gas, hybrid and electric buses. The method we used to calculate the bus noise was Nord2000, which is a more advanced method of calculation than the one usually used for calculations in Sweden, i.e. the Nordic Prediction method from 1996 (RTN: 96). The advantage with Nord2000 is that you can use specific input data for each bus type, something that is impossible with RTN where in-data for light and heavy vehicles are based on measurements carried out in the early 1990s. Nord2000 has been implemented in different noise calculation software, of which SoundPLAN is the computational tool used in this project. The drawback with SoundPLAN however, is that it is not possible to calculate maximum sound levels with the Nord2000 model as this has not been implemented in the software. For calculations with Nord2000 new input data has been collected based on measurements of gas, electrically charged hybrid buses driving in diesel mode, and electrically charged hybrid buses driving in electric mode on a test track in the autumn of 2016. For diesel buses existing input data for Nord2000 was used based on measurements in real traffic in 2015. The results of these measurements are used not only to do outdoor calculations of bus noise, but also for calculations of indoor noise.
Another disadvantage of Nord2000 is that the calculations are more time consuming, which meant that we had to limit the geographic calculation area to 32 km2 in central Gothenburg. It is the most densely populated area in Gothenburg is where the bus traffic is most intense. In this area, bus traffic along with car traffic and other heavy vehicles was calculated within 100 meters from the road center, as well as within 30 meters of all bus stops to see the effect of starting and stopping on noise levels.We have also calculated a small residential area in the center of town where buses dominate namely the area around Bäckegatan, to analyze the impact of bus traffic noise in more detail.
Measurements of the various bus types demonstrates that there are differences between the bus types and that diesel buses cause more noise than the other bus types. A frequency analysis of the sound also shows that the sound from diesel buses contains much more low frequency sound than electric buses. Gas and hybrid buses lie somewhere in between when it comes to the content of low-frequency sound.
The estimates of the health effects and economic costs of bus noise show that diesel buses cause the highest costs of the various bus types included. But despite electric buses being perceived as much quieter it is in general difficult to show any significant difference between the bus types, even if hybrid buses in diesel mode and gas-powered buses contain more low frequency sound than electric buses. There is however a greater difference between bus types at bus stops because diesel, hybrid bus in diesel mode and gas-powered buses make a lot more noise than electric buses during acceleration. When the buses are calculated together with other road traffic, the other road traffic tends to dominate due to the fact that the volume of other traffic tends to be much greater than the volume of buses.
However if you only have bus services near homes (without other traffic), the differences in exposure, especially from 55 dBA and above, is large between bus types and the electric bus is by far the quietest option. For exposure at night, calculated both with buses only and with buses and other traffic included, the differences in exposure to sound levels that can cause sleep disturbances are greater between bus types, and electric bus clearly contribute least to increased sleep disturbance.
Research shows that the link between annoyance to and loudness of noise from heavy traffic, measured or calculated as a daily equivalent noise level in decibel A, is not particularly good. Low-frequency sounds are perceived as more disturbing and are perceived as louder than sound sources that are dominated by sounds in the higher frequencies, such as car traffic. The methods for quantifying the health impact and economic costs of traffic noise need to be developed or supplemented by other methods which more accurately include annoyance and sleep disturbance from heavy traffic in order to be able to make more accurate cost-benefit calculations.