Emergency Services' (ES) vehicles primary objective is to attend an accident or other incident scenes in a fast, safe and efficient manner. Yet this task is becoming increasingly difficult due to the increasing population and the plethora of emergency cases. These factors affect directly the traffic both within the urban and the rural environment, increasing dramatically the "time to arrive" at the point of interest. Numerous Head-Down Display (HDD) systems have populated the dashboard area of the ES vehicles in order to tackle this issue, with limited success. To this end, the development of emerging technologies in both computing and telecommunications have enabled modern vehicular systems to assist drivers in their decision-making process. Head-Up Displays (HUD) present a combinatory approach of the aforementioned technologies, which present crucial information to the driver through Augmented Reality (AR) projection. In order to develop a design and development framework for the utilisation of AR and HUD technology, this paper presents the results of 50 drivers investigation related to their activities during immobile or slow-moving traffic which results in driver's distraction and inability to respond to the incoming ES vehicles. In turn, the paper discusses these results and offers an overview of the Human-Machine Interface requirements for a prototype HUD aiming to assist the safety, speed and manoeuvrability of the ES vehicles.