The modern-day vehicle hosts a complex environment where competing goals challenge the act of driving. Drivers may pursue Non-Driving Related Activities (NDRAs), resulting in multitasking. How NDRAs are achieved will depend upon whether In-Vehicle Information Systems (IVIS) are available. If not, alternative means may be taken that could compromise Driving Related Activity (DRA) performance. Situation Awareness (SA) is central to achieving multiple goals in a dynamic environment. This thesis investigates an Unconstrained approach to designing IVIS to examine how to improve multitasking performance in-vehicle through enhanced driver SA. A combination of theoretical and experimental activities were performed. A literature review in SA theory exposed a lack of detailed consideration for competing goals and task switching. A restated model of SA was proposed to show the impact on Situation Assessment and the Situation Model of the act of multitasking. Using a new methodological approach, a series of simulator experiments then aimed to measure and characterise the effect of increased awareness on task performance when multitasking. The results demonstrated that increased awareness improved task performance, therefore, providing scope for IVIS to achieve the same. Subsequently, by using the model proposed, IVIS concepts were designed to support either the NDRA or DRA, and a simulator experiment was performed. Supporting NDRAs using Contextual Cuing proved successful by reducing the cost of task switching, but impacted overtaking behaviour. Supporting the DRA, while successful for Lane-keeping, did not operate as intended. Drivers were not able to adequately use concurrent feedback due to not achieving a skilled level of behaviour. Finally, increased awareness impacted how a driver manages their attention. Drivers acted more strategically, showing evidence for dynamic compensatory metacognition. Therefore, by using SA to understand the vehicle environment, in detail, and taking an Unconstrained approach to IVIS design, improved in-vehicle multitasking performance can be achieved.