Reliability, Availability, Maintainability and Safety (RAMS) assessments have long been part of development of tunnel ITS designs, and are now an emerging requirement for complex motorway installations, albeit excluding the Safety assessment element. This paper discusses a Reliability, Availability, Maintainability and Human Factors (RAM HF) review recently delivered for a complex motorway ITS design.
Reliability is the likelihood that a system will perform its function without failure at any specific time. Reliability relates to frequency and impact of failures and is measured using Mean Time Between Failure (MTBF) and Failure rate – the number of failures over a specified time. Availability is calculated as the percentage of time (or probability) that a system is operational and can perform its function under normal circumstances. Reliability and Availability are closely inter-related. Maintainability relates to how difficult a product or system is to access and maintain, as well as the necessary frequency of the maintenance task. A design compromise can result in greater maintenance requirements to ensure availability remains high enough.
Human factors refers to the application of the human sciences (psychology, physiology, biomechanics), to the design and operation of systems, to ensure that systems are safe, easy, and comfortable to operate and maintain. When human factors methods and tools are integrated throughout the systems engineering and design process, from its earliest stages, the risk of having to make costly design changes at later project stages, due to usability or safety issues, is substantially reduced. Human Factors helps to uncover potential sources of user error or frustration, as early as possible, and can help to inform difficult design decisions that have the potential to affect ITS end-users.
The RAM HF process is important to undertake in parallel with the design development, to ensure that road user, operator and maintainers needs inform device types and placement and that these in turn inform maintenance and operating procedures; optimised power and communications designs; and hardware procurement.
This paper presents the approach taken and observations on how ITS designs can be shaped for very constrained sites to ensure optimal RAM HF outcomes.
