Whole-Body Vibration Exposure Studies on Train Operators (1991 to 1995)
Nihat Özkaya (PI), David Goldsheyder, Ben Willems, Margareta Nordin
The OIOC research team conducted two field studies to measure vibration levels experienced by New York City subway train operators. The specific aims of these studies were to measure mechanical vibrations transmitted to the train operators, to calculate daily whole-body vibration exposure levels and compare these levels with acceptable exposure levels according to the international standard on whole-body vibration (ISO 2631), to identify factors that may influence vibrations levels, and to determine the vibration characteristics of new operator seats and new-technology trains.

To determine the vibration levels transmitted to the operators who were assigned to work at different lines of the subway system, the vibration measurements were carried out by dividing the subway system into subway lines, each line into southbound and northbound directions, and each direction into station-to-station observations. Measurements were made on all subway lines and for all car types used in the subway system. For each subway line, at least two round trips of data were collected. A total of 48 round trips were made and more than 100 hours of vibration data was collected and analyzed. To be able to compare the new seats and the new-technology trains with the old ones, vibration measurements were made under conditions for which all variables other than the operator seat or subway car were constant. The results obtained were analyzed to assess the effectiveness of each seat and car type tested in reducing the mechanical vibrations transmitted to the train operators.

As a result of the first field study, it was determined that six out of twenty subway lines had vibration levels higher than the daily exposure limits according to the international standard. It was also determined that train speed was the most significant factor influencing the vibration exposure levels. The analyses revealed that there were varying degrees of vibration transmissibility between different car types used in the subway system. Different cars of a single car type could transmit vibrations differently as well. This suggested that car maintenance was another factor that influenced the vibration levels. There was not a significant difference between rush hour and non-rush hour vibration levels. That is, passenger load did not influence the vibration levels significantly. The continuous or welded rail contributed less to the vibration levels than the bolted rail. The operator experience in terms of the number of years on the job was observed to have some effect on the vibration levels. The more experienced the operator, the lower the measured vibration levels.

The results on operator seats demonstrated that while it is very important to consider operator comfort and ergonomically correct posture, the vibration transmissibility must also be addressed during seat design. The new seats tested in this study may be satisfactory for use in a static environment, but will not protect the operator from the long-term effects of vibration exposure. Even though the two new-technology trains were tested on only two subway lines, both trains can be utilized to reduce the vibration levels transmitted to the train operators and hence reduce the possible adverse health effects of whole-body vibration exposure throughout the divisions of the NYC subway system for which they were designed.

These study were sponsored by the New York City Transit Authority. It is our objective to extend these studies to investigate the effects of vibration exposure on the health and performance of train operators.