Travel time functions specify the relationship between the travel time on a road and the volume of traffic on the road. This report summarises the results of an initial exploratory review of the alternative approaches for developing a set of travel time functions for Adelaide. A two dimensional classification is used to characterise the range of alternatives. The first dimension is based on the network level used when estimating the travel time functions. Four network levels are identified: area, corridor, route and link. The second dimension relates to the source of data used in estimation and we distinguish between existing data and new data. A range of cost and benefit measures are identified for evaluating the alternatives. The costs of developing travel time functions include data collection costs and analysis costs. The benefits relate to the performance of the alternatives in the application context, where the application context refers to the type of model which will use the travel time functions as an input. Three application contexts are defined: policy, sketch planning and detailed planning. The benefits include the potential for reducing the prediction errors in the application context, the level of application flexibility and the policy sensitivity of the travel time functions. In general, the costs and benefits increase as the travel time functions are calibrated at finer levels of network detail. There is limited scope for developing travel time functions from the existing Adelaide data. A data collection scheme is proposed which entails using the acts system to collect volume data in conjunction with future raa travel time surveys. The proposed scheme should produce travel time functions suitable for use at the policy and sketch planning levels.