Example

Robert Jensen takes the train from his home to his workplace each work day. His daily round-trip train ticket costs $10.00. Every few months he must bring drafting tools and display charts to his workplace for a presentation. When he transports these tools and materials he uses his car instead of taking the train. Driving to his workplace costs him $20.00 in gas, tolls, and parking fees. However, Jensen cannot deduct the extra $10.00 it costs him when he drives to his workplace, since he would have spent that amount driving regardless of what he was carrying with him.

If, however, Jensen's tools and materials were so bulky that he had to rent a trailer to carry them, he could deduct his costs for renting and parking the trailer.