The sample is biased because the train riders are more likely to favor better rail road services than the other commuters who use other means of transport.
Step-by-step explanation:
The statement in the question is misleading because the sample from which the survey has been conducted by the researcher is a biased sample.
The word commuters used in the statement includes all the people who use other modes of the transportation also like bike, cars, buses etc. It does not only include the train riders. Thus it is a biased sample. Only train riders would favor a higher tax for improving railroad services not all commuters.