The DIATS project, funded under the European Fourth Framework programme is assessing the ‘most-likely’ deployment scenarios for inter- and peri-urban based, co-operative ATT systems. The project will help decision makers identify clear paths and timetables towards maximum benefit system implementation.The results of a Delphi study of the most likely implementation scenarios are presented. Simulation of the impacts of a range of Advanced Transport Telematics (ATT) applications is being undertaken using several models and data from an Instrumented Vehicle. Results of the cross-validation study for the models are given. The paper also presents discussion on the behavioural, safety and legal implications of implementing new ATT scenarios which incorporate Adaptive Cruise Control (ACC).