Billing Ethics - Do you pass the Quiz?

The Wall Street Journal Law Blog recently ran a quiz on billing based on a hypothetical posed by the American Bar Association. The question posed by the ABA was:

You are taking a two hour plane trip from Chicago to New York to conduct a deposition in a matter involving client A. While on the plane, you review materials for a brief you will be filing for client B the following week. You normally bill clients for your time spent traveling on their behalf.
Can you bill clients A and B for two hours each for a total of 4 hours?

What would you do?
Many of the Wall Street Journal respondees got it wrong. The ABA ethical opinion (consistent with the Australian position) is that it is unethical to double bill. The travel time billed is to cover "loss of opportunity", and if the lawyer does other work in this time, there is no opportunity lost.

The dilemma posed demonstrates one of the difficulties of hourly billing. Both the travel (and associated inconvenience) and the work performed during the travel time, provide value to the respective clients. An alternative billing arrangment whereby a fixed fee or fee for value is agreed may help avoid this problem.