Whereas the proper object of all commercial transportation is profit-making, the navigational objectives of taxis and of airliners differ remarkably. In airlines navigation only affects product quality and operating costs but in taxis the revenue (the fare on the meter) is a function of the navigation. Regularity of service is meaningless to taxis whereas regularity of schedule keeping is an imperative of airline navigation because it is only possible to offer air fares a full order lower than taxi fares on aeroplanes costing up to $200,000 a seat by achieving high equipment utilization. Many taxi drivers hire their cabs at a weekly rate which includes maintenance and repair but not fuel. They therefore have a direct interest in the cost of fuel but not in wear and tear of machinery. Finally, taxi drivers are self-employed businessman whose income depends entirely on their navigational skills.