D20.33 Functional Requirements
This report consists of an in-depth analysis of the functionalities of the SASPENCE system to be designed and developed. This analysis is aimed at providing a list of functional requirements which show how the SASPENCE application should operate in different conditions. SASPENCE (Safe Speed and Safe Distance) is a support system that assists the driver in avoiding accidents related to inappropriate speed and/or too short headway. It provides a seamless cooperation to the driver, suggesting him/her the most adequate speed/distance/trajectory according to the actual driving context. The results from this analysis will mainly constitute an input to the definition of technical specifications.
Some basic definitions are included at the beginning as introduction, showing also the methodology used for the application of the Functional Analysis tool. The Functional Analysis itself is then developed from the definition of situations of use of SASPENCE to the outlining of diagrams which reveal connections and functional relations between surrounding elements. The result of the Functional Analysis is a list of functions.
Then, these functions are described in detail, specifying their possible values based on objective criteria from some literature review findings and technical data. The concepts of Safe Speed and Safe Distance are explained in detail, revealing the strong mutual relationships and thus contributing to a precise definition of the project scope and clarifying the actual objectives to reach. Specifically, the SASPENCE concept (i.e. the concepts of Safe Speed and Safe Distance) is reviewed by analysing the system functionalities and studying different related points of view and legislations in Europe. As a consequence of this literature review, guidelines are proposed, concerning influencing parameters and criteria to follow for the calculation of speed and distances which are safe for certain driving situations.
It is important to highlight the great variability in the ways of addressing this safety issue, although most of them share opinions about what is a safe distance and what is a safe speed. As revealed in the document, a safe distance is commonly defined as a following headway that is enough to avoid a collision if the preceding vehicle suddenly decelerates or brakes to stop. And a safe speed is defined as a speed that allows drivers to stop comfortably on their own side of the road and within the distance that they know to be clear.
As a consequence of this review and analysis of the SASPENCE concept, the requirements to be taken into account in the system development are listed and explained. These requirements are referring to functional needs that SASPENCE is required to comply with. In this way, an overall system functional definition is offered, revealing how SASPENCE should operate. In particular, a set of parameters has been outlined and proposed to be considered as computation variables for SASPENCE, setting the basis for the definition of an algorithm expression that calculates which safe distance and which safe speed should be kept for any given driving context.