Bus and tram drivers

Distributions of accident frequency often provide surprising results. A small number of people are responsible for most of the accidents which occur in a population. Lejeune (1958) reported, for example, that in a study on bus and tram drivers who were exposed to relatively equal risk situations, 10 % of the employees with the highest accident rates were involved in 30 % - 70 % of all accidents. This observation appears to coincide fully with the personality concept of the accident-prone person. It seems that there are particular personality factors and traits like immaturity, risk-taking behavior, or lack of self-confidence which facilitate the occurrence of accidents. 

Hakkinen (1958) presented a study on Finnish bus and tram drivers, in which the control of the hazards over a longer period of time was accomplished. The aim of Hakkinen s study was to investigate the value of certain psychological tests for detecting various levels of accident proneness. A group of 322 bus drivers and a group of 363 tram drivers exposed to the same traffic conditions for up to eight years were the subjects of this study. 

The homogeneity problem in terms of time exposure of the bus and tram drivers could be solved, as they all worked the same number of shifts per day. The equal hazard exposure requirement was more difficult to meet. Investigation of various routes taken showed that the accident index differed markedly. Because of a constant interchange of drivers on these routes, Hakkinen could demonstrate by means of correlative methods that this was indeed responsible for producing the effect of balancing hazards, especially over long periods of exposure. 

Personal accident records of the drivers contained all accidents, irrespective of outcome and cause. The reliability of these accidents was tested on five different groups of bus and tram drivers with exposures ranging from two to eight years. Correlating the accident figures of two successive 4/4 years produced highly significant coefficients, bus drivers r = 0.58, corrected by Spearman Brown r = 0.73 for tram drivers r = 0.67, corrected by Spearman Brown r = 0.81. Results are shown in Tab. 5.8. 

A recent study measured PM2 concentrations in both old and modem models of buses and trams in Helsinki (Finland) during a 2-week period from mid-June to the begirming of July 2005 (Asmi et al. 2009). Measurements included four sets of 2-day trials. Bus and tram routes were mostly coincident. Sampling time was limited by the vehicle operational shift period. In both bus types and the older trams, the cabin space was open. In the modem trams, a separate driver s compartment was equipped with air conditioning. Mean PM2.5 values for the first... 

Nevertheless, these possible negative health effects have become a growing concern also among job categories that are occupationally exposed to urban PM. In fact, policemen, traffic wardens, professional drivers (tram, bus, taxi, lorry and truck drivers), roadside vendors, postal workers, street sweepers and other outdoor urban workers spend most of their work time exposed to urban PM. Although it has been difficult to demonstrate the relative risk of death or illness associated with PM, researchers have reported a number of health effects on workers (Gamble and Lewis 1996). In this section we review the adverse health effects observed in workers exposed to urban PM. 

As mentioned earlier, Hakkinen (1958) employed various psychological tests for discriminating levels of accident proneness. He succeeded in establishing a very stable accident criterion due to the homogeneity in road hazards. The accident records of these subjects provided a retest reliability with split half correlations of the first four years/second four years and odd/even years (in brackets) bus drivers r = 0.58 (0.68) tram drivers r = 0.67 (0.73). 

A similar study was conducted 10 years later in 16 air-conditioned buses and 15 non air-conditioned trams in the city of Hong Kong (China) (Jones et al. 2006). The concentration of PMio was measured using an aerosol monitor placed next to the driver s seat. The levels of PMio in air-conditioned buses were 265.4 83.2 pg/m (mean standard deviation), while in non air-conditioned trams values were 161.1 103.1 pg/m (mean standard deviation). The authors hypothesized that the air filters in the air-conditioned buses were not adequate to filter out larger particles as well as dust and maintain an optimal air-conditioning system within the bus compartment. 

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