There are a number of standard computer “packages” available for the task of vehicle scheduling. The earliest versions of these packages were fairly inflexible in that they had certain in-built assumptions. Typical, an understandable, assumption might include vehicle capacity limitations, driver's time limitations, customer earliest/latest delivery times, etc. These computerised models did not incorporate all of the constraints placed upon the logistics operations of an enterprise. For instance, programmers could not anticipate how transport personnel would react to the “imposition” of a mathematically calculated route that test no cognisance of their local knowledge and experience or the idiosyncratic wishes of some customers. This being the case, programmers were unable to build in all of the factors which should be taken into account when designing a delivery route. As a consequence, computer generated vehicle schedules were sometimes sub-optimal, sometimes unrealistic and often resented by those who had to implement them. To improve computer-based routing, interactive computer scheduling has been introduced. Interactive computer scheduling allows the transport manager to alter any of the parameters in the mathematical model in line with his/her view of the real situation. Thus, contemporary computer-based vehicle scheduling models combine the manager's knowledge with the computer's ability to process complex mathematical models, quickly, to produce flexible schedules.