One of your very important initial steps at this phase of the project is to develop your Design Requirements and your Design Specification documents. To give you an idea what these documents are and why they are important, I quote below from an email sent to me by one of the mentors for the project who has extensive industry experience with transportation projects about the process they follow:
To start with I am most interested in reviewing a document that discusses the design goals and objectives, a Design Requirements document. This document should discuss what the design is to achieve in plain English and will be referred to during the entire design process. The real world analog to this document would be the Planning and Design Criteria documents we produce and review during the early stages of a project.
The next level down would be the Design Specifications document(s). This document, or set of documents, still in plain English will layout how to go about achieving the goals and objectives in the Design Requirements. The real world analog to this set of document is the actual Contract or Proposal documents for a transportation system.
The next level down is the system level design documents. These documents explain in plain English the desired functions of each subsystem, including how each subsystem is to interface with the other subsystems. A subgroup of these documents is the Interface Definition documents which provide more specifics on the interfaces.
The next level down is the selection of hardware and software, by subsystem, to accomplish the system functions.
The next level down is the actual design of the hardware and software on a subsystem by subsystem basis.
The next set of documents is the testing criteria for each subsystem. This set of documents contains detailed test procedure specifications on how to go about testing each of the functions of each subsystem to demonstrate that what was built meets with requirements. This can be done in either one or two phases.
The development of each lower level set of documents must be performed by consulting the higher level document.
While your set of documentation will not be as extensive as what would be used on a full-blown industry project, I would like the subteams to follow the approach outlined above as far as it makes sense for your sub-projects. To give you a feel for what a professional Design Requirements document looks like, see my comment to blog post #2 and view Appendix A from the Aerospace Corporation report on the study of ATN from the Mineta Airport to the proposed BART terminus:
look at the Appendix from the Aerospace Corporation's report on the City of San Jose's study of ATN from the Mineta Airport to the planned BART terminus. Pp. 247- (A1-A124). The report can be found here: http://www.sanjoseca.gov/DocumentCenter/View/14328
