Other modules

As explained in the introduction, a micro-simulation in a software suite for transportation planning would have to be run many times (``feedback iterations'') in order to achieve consistency between modules. For the microsimulation alone, and assuming our 16 CPU-machine with switched 100 Mbit Ethernet, we would need about 30 hours of computing time in order to simulate 24 hours of traffic fifty times in a row. In addition, we have the contributions from the other modules (routing, activities generation). In the past, these have never been a larger problem than the micro-simulation, for several reasons:

• The algorithms of the other modules by themselves did significantly less computation than the micro-simulation.

• Even when these algorithms start using considerable amounts of computer time, they are ``trivially'' parallelizable by simply distributing the households across CPUs.^25.5

• In addition, during the iterations we never replan more than about 10% of the population, saving additional computer time.

In summary, the Transims modules besides the traffic micro-simulation currently do not contribute significantly to the computational burden; in consequence, the computational performance of the traffic micro-simulation is a good indicator of the overall performance of the simulation system.