A guiding principle in choosing a model for a transport assessment is theappropriateness of the modelling tool for the job taking into account thescope of the task, the needs of the stakeholders, and the resources available. When considering the use of a micro-simulation model, a key questionto ask is: Would a more traditional (non micro-simulation) model meet therequirements? Despite the claims of micro-simulation developers, for the vast majority of transport assessments there is no evidence that a pure micro-simulation approach is the most appropriate. For most cases greater understanding of the operation and performance of the network can be obtained better and much faster from a more traditional approach. A major flaw with micro-simulation models is their inability to consider capacity explicitly which is a key indicator when you want to learn about a network. With a traditional traffic assignment model it is clear where the network is over capacity and where there is spare capacity that can be utilised. It is very difficult to answer such questions with a micro-simulation approach. It is not possible to work out where the bottlenecks are or where they would shift to if any were removed. The increased detail offered by a micro-simulation is considered to be spurious modelling in finer detail that doesnot necessarily produce more accurate answers and is not worth the hugelyincreased computer run-times. Another major weakness with micro-simulation models is their lack of any academically accepted route choice methods. The ad-hoc route choice algorithms utilised by the commercially available micro-simulation models are not based on any sound principles such as Wardrop Equilibrium. They are also often unstable particularly in congested networks where gridlock can occur and they have problems with convergence. They also cannot deal with fundamental issues such as elastic assignment orvariable demand modelling. This makes micro-simulation inappropriate for any networks where route choice is a key issue such as whole town centres.This study explores these problems in more detail and provides advice on when micro-simulation is most effective. It also describes how new products are coming to the market that provide tools that seamlessly integrate macro, micro and meso modelling together allowing the best approaches to be combined effectively. For the covering abstract see ITRD E145999
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