This study has a very clear relevance to a driving task, since it involves a highly visual, time-sensitive, and continuous main task and a visual secondary task which obscures information used in the main task. This version condenses much of the discussion of validity and some of the analysis from the dissertation version. The results highlight the complexity of the design question and the need to clearly prioritize which aspects of driving behavior we wish to support. The strong performance under a negotiated interruption strategy is promising and should be investigated. If the driver must be interrupted in a Notify style for some reason, this may be the best way to do it. There may also be some benefit for the Check and Continue switch types. Even in this task, where cognitive workload was easy to estimate, the mediated interruption strategy produced mediocre performance. Workload estimation is likely to be unreliable and highly impractical under realistic driving conditions, making this option even less appealing. The scheduled and immediate interruption strategies produced unacceptably poor performance on the main task and should probably be avoided in a driving context.