Assessment of electric and diesel urban bus tire wear in fleet operation.

Abstract

"Electrification of mobility is a key element in policies that aim to improve air quaility in densely populated urban areas. As part of such a strategy all public transportation in the Netherlands is required to be zero emission by 2025. One of the first to implement this requirement is the Eindhoven region, where 43 electric buses have been in operation since december 2016. Electric vehicles produce no pollutant gases, but there is some concern about increased airborne particulate matter emission due to higher tire wear rates. However, in the literature, very little actual data can be found on this matter. This paper presents the outcome of an investigation aimed at assessing tire wear of comparable diesel and electric buses while in operation and with little or no impact on this operation. In the study two diesel buses and 3 electric buses were monitored, all of them operated by Hermes/Connexxion. All buses were 18 m articulated buses. For best accuray, direct measurement of tire weight loss at intervals would be the obvious measurement technique. This approach was however unacceptable to the fleet owner as it would have too much negative impact on the fleet operation. Also, dedicated accurate (vision based) thread monitoring equipment was not available. Hence, tire mass loss was determined from the measured reduction in tire tread groove depth at twelve different locations that were evenly distributed on the tire envelope. This measurement was performed on all three axles and was repeated several times over a nine month period. From the resulting data the average tire groove depth reduction in mm per 10.000 km was determined. The results show that the tire wear rate on the electric buses, even when compensated for their higher gross vehicle weight, significantly exceeds that of the diesel buses. The difference is analysed and discussed. Finally, by comparing weight loss measurement with tread depth reduction, also an indication of weight loss is determined and compared with current emission factors."