resolutionmini

haut de page

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

haut de page

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

haut de page

mise à jour du
19 décembre 2002
Hum Ergol (Tokyo)
1975;4(2):115-27  
lexique
Driving and subsidiary behavior of taxi drivers working alternate-day shifts
Kazuhiro Sakai and Yukichi Takahashi
Division of Work Physiology and Psychology, Institute for Science of Labour, Sugao, Takatsu-ku, Kawasaki, Japan
Division of Social Sciences, Institute for Science of Labour, Sugao, Takatsu-ku, Kawasaki, Japan  

Chat-logomini

 
ERGOLOGY
 
The working time of taxi drivers in large cities of Japan is characterized by the fact that they work on alternate days for as long as 16 hr or more. The extent of prolonged hours of work by taxi drivers is relatively well documented. A statistical survey by the Ministry of Transportation in 1973 revealed that the average monthly working hours of taxi drivers were more than 210 hr, the mean monthly sum of portal-to-portal hours amounting to nearly 270 hr. While it has been suggested that their workload has close relation to the incentive wage system on the basis of the total of fares, there are few reports making refèrence to the interaction between the wage system and the actual mode of work by taxi drivers. Further studies seem necessary in this respect, since the prolonged hours of work alone cannot be easily rectified so long as the wage incentive continues.
 
The long working hours of taxi drivers bring with thera frequent night work. Special emphasis bas been laid on fatigue and unhealthy working conditions of taxi drivers by some field reports. It is generally agreed that the usual 16-hr shift system produces marked changes of physiological parameters. It has been further pointed out that many drivers who are involved in frequent night work, normally 13 nights per month per taxi driver, are subject to diseases of digestive and other organs. Thus the Committee for Driving Work and Safety of the Japan Association of Industrial Health submitted a report in 1974 reviewing results of field investigations and recommended intensified occupational health measures for vehicle drivers. The report further stated that the working hours of occupational drivers should be reduced to 8 hr or less within the 24-hr period beginning from the shift start. In fact, however, the 16-hr shift system is still widely employed among taxi drivers, except for a small number of companies where rotation systems with a shift duration of 8-12 hr have been introduced.
 
The above report also outlines the effects of continued driving on the drivers' performance, which seem as important as are the environmental factors accounting for the traffic accidents. It is the purpose of this study to examine the effects of the long shifts of alternate days on the taxi drivers' performance. It is felt that the direct observations of the manner of work of drivers during the whole shift period may contribute to the understanding of the behavioral changes according to the shift system. Daily reports by drivers, readings from individual tachograms, and time records of daily living by means of the diary method are also referred to. [...]
 taxi
BEHAVIORAL CHANGES
 
Changes of driving performance by time of the day
 
The taxi driving performance changed in a very characteristic way according to the time of the day. The major factors of the changes were the rate of meeting passengers, the mean distance per hire, and the general traffic conditions. As shown by Fig. 3, which is based on reports of 100 shifts, the hourly income was not proportional to the rate of the duration of running on hire and fluctuated greatly during the day. The hourly income was relatively high in the morning due to a high percentage of the hired running. In later periods, the rate of carrying passengers remained almost constant at around 50%. The drop of income at the lunch time and in the evening was due both to taking meals and to smaller fares per hire in the evening. A sharp rise in the last periods later than 22:00 is seen both for the fare per hire and for the hourly income. The high levels continued even after midnight. The income per hire was only Y 340 in the first period of the shift, a little more than the minimum fare of Y 280, indicating that most passengers used the car for short distances. The mean income per hire was maintained at around Y 450 to Y 550 from 9:00 to 22:00, but it rose to Y 600 to Y 700 in the hours later than 22:00. It was mainly because passengers at night usually hired the taxis for middle- or long-distance drives.
 
In addition to this, the difference in traffic conditions between daytime and night also favored the income increase at night. It is shown by Fig. 4 which indicates the mean driving speed and the mean fraction of the time when the car remains stationary for different periods of the shift. The data for 2 whole shifts are shown. Both curves were almost symmetrical. The mean speed was only 21-22 km./hr in the morning and evening rush hours when the car was brought to a halt for about 35 %. of the time. The average speed in the middle of the day was about 30 km/hr, while it increased to 34-39 km/hr in the periods later than 22:00, when the car stopped remarkably less for only 15 % of the running time.
Thus, the increase of the gross income at night was evidently the result of the combined effects of longer distances travelled and more favorable traffic conditions in late hours than in the other periods. Such a situation is characteristic of large cities like Kawasaki. These facts explain the reason why the late night hours are very important for taxi drivers in order to increase the total amount of income for the day's work. It was common to, all the drivers inquired that they ,waited for the night hours and tried to increase the income at night rather than in the daytime. Very unfortunately, these relatively gainful periods began at around 22:00, when nearly 15 hr had past since the shift start and when the drivers were influenced by the prolonged work and the circadian rhythm.
 
Changes of subsidiary behavior by time of the day
 
The taxi drivers' subsidiary behavior which is apparently irrelevant to the driving performance was recorded by an observer who sat in the assistant's seat during the whole shift. Table 3 summarizes the results of observations on two shifts for six different categories of subsidiary activities in four periods of driving interspersed by pauses for breakfast (around 9:00), lunch (around 13:00), and supper (around 19:00). The mean rate per 5 min of each kind of activities is indicated. The mean rate was 4.32, 2.54, 3.81, and 4.43 in periods I,II, III, and IV, respectively. The changes were mainly due to changes in the rate of the upper limb movements and that of changing sitting positions. The rate of looking aside while driving decreased slightly as the time progressed. More remarkable changes were found for those activities which had relatively low rates at the beginning of the shift. Compared with the first period, the subsidiary shoulder-neck movements became 1.5 times more frequent in period IV, lower limb movements 2.2 times, and yawning 3.4 times.
 
The cumulative frequency distribution of those subsidiary activities are illustrated in Fig. 5 for six different kinds and for the four periods. The distribution pattern differed greatly among the periods. In the case of the upper limb movements, they tended to repeat more than twice per 5-min interval in more than a quarter of the observations of periods III and IV, while lower limb movements, shoulder-neck movements, and yawning were liable to repeat twice or more when they occurred in period IV. Such a tendency was most conspicuous for yawning which was specific to period IV, often appearing in bursts in drowsy conditions.
 
A certain relation between the rate of subsidiary behavior and the driving performance is suggested by Fig. 6 showing changes in the total rate of such activities separately for driving with frequent stopping for 30% or more of the time and that with stopping for less than 30% of the time. Driving with less frequent stopping produced less frequent activities in the first period, but in later periods, especially in period IV, the subsidiary activities were seen to increase greatly also in driving without frequent stopping.
 
Figure 7 gives recordings of subsidiary activities on three occasions within a shift of a driver. It is demonstrated that some of subsidiary activities became correlated with the driving performance as fatigue developed. At 11:30-12:00, in the 5th hr of work, the driver was in good humor and was attempting to locate passengers utilizing wireless communication with the service office. At this time of the day, his subsidiary activities were least frequent, and each of such movements appeared rather sporadically without any distinct interrelations with the others. At 22:00-22:30 when he had been out for more than 14 hr, subsidiary movements were very frequent and multifarious. Yawning was seen in bursts together with some sitting position changes and with the suppression of upper limb movements. Repeated changes of the sitting posture seemed to have resulted not only from fatigue but from drowsiness. This was more clearly confirmed by similar recordings at 2:00-2:30, nearly 19 hr from. the departure time. When a passenger got off at 2:30, the driver confessed that he had been very drowsy some time ago. Actually at about 2:10, the driver had a very sleepy look and even closed his eyes when the car stopped for a while at a red signal. The combination of yawns with sitting posture changes was typical for that period, the other subsidiary movements being temporarily infrequent. Later on, the latter increased again.
 
CONCLUSIONS
Based on the results of this study and our previous report, it can be concluded that the alternate-day shift systerm of taxi drivers virtually influences the daily course of their driving performance as well as significantly degrade their performance capacity. It has been reported by SAKAI and TAKAHASHI (1975) that 49% of the inquired taxi drivers had to go to the next shift without sufficient recovery from the fatigue of the previous shift, and that the alternate-day shifts of 16 hr produced a significantly more frequent rate of subjective fatigue symptoms and sleep deficit than did the 12-hr shift system. Although the present study was not specifically concerned with physiological changes of drivers, these observations lend support to the assuraption that the taxi drivers are working beyond the physiologically tolerable limit suggested by many investigations and by standards of road traffic.
 
Studies on effects of prolonged driving have been generally concentrated along two lines of examination, one of these has been concerned with changes in driving behavior, and the other has examined the physiological and psychological correlates of driving. There are enough evidences indicating a demonstrable fatigue effect of a long automobile drive, while the relevance of behavioral changes to driving situations has been suggested by some authors
 
The examinations of the drivers' subsidiary activities may also be useful, especially when the intensity of driving work changes towards the end of a shift, as is the case for the city taxi drivers. Although the observed changes of subsidiary behavior in the present study may not be directly relevant to those in monotonous factory work reported by KISHIDA (1973) and others, effects of monotonic driving in a fixed posture should also be taken into account. It would be reasonable to assume that the remarkable changes in the taxi drivers' subsidiary behavior were produced not only by prolonged working hours but also by degradation due torather monotonic driving situations. Night work seemed to accelerate both of those effects.
 
The effects of the alternate-day shift system have a close relation with the incentive wage system. The intensity of work in terms of the driving speed and distance is enhanced towards the end of the long shift seemingly 'voluntarily.' This is because intensive work during late night hours secures the daily income, since the running distance on hire can be increased more easily in these hours than in the other periods of the day. The same reason also accounts for the prolongation of working hours and reduction of resting periods. Results of our previous study has indicated that a majority of the taxi drivers are conscious of the harmful effects of long hours of work, 51 % demanding a reduction of the shift length, 35% urging a reduction in the number of days of work instead, and only 9 % favoring the present system (. Although the situation is rather complex due to the interactions of the incentive wage system. with traffic circumstances in cities, effective means should be explored to eliminate the existing alternate-day shift system of the taxi drivers of this country.
 
Temporal change of subsidiary behavior in monotonous work.Kishida K
Driving and subsidiary behavior of taxi drivers working alternate-day shifts Sakai K
Drowsiness, counter-measures to drowsiness, and the risk of a motor vehicle crash Cummings P