User Interfaces (UIs) are by definition the most visible part of any technology project. For brevity, both dispatcher and passenger-facing UIs are lumped together. This is not my specialty; rather than rehashing details, I’ll point out two excellent sources for introductory content, and then cover a couple questions that must be considered when buying an AVL product.
Usability.gov maintains an excellent library of public-sector focused content related to usability, user interfaces, and user experience. This article might be an excellent entry point. If that seemed too simple and you’d like to get your feet wet, check out the lessons at Hack Design.
Before beginning procurement, the most crucial UI-related decision is what are the use cases for the product?
UIs are typically distributed as a client or via a web-interface. Regardless of the choice, the two most crucial technical questions surrounds the dependencies required– are there any required libraries or plugins for it to function, and will it run on a tablet or smartphone? While PCs are currently standard issue, the marketplace is changing rapidly. Even if mobile devices are not in your requirements, during the life of your AVL project someone will want to access the system on one.
Finally, no web-based user interface should be accepted if it does not run on a recent version of Chrome, Safari, or Firefox on a desktop computer. Some AVL vendors are still hocking products that require outdated versions of Internet Explorer, and these should be avoided like the plague. Similarly, plugins such as Flash and Silverlight are slowly dying and are a constant source of security vulnerabilities; any system requiring them should be considered carefully.