As regards to transportation, function is the connection bridge to user. The object or system has to provide immediate availability and feedback; it has to be straight forward.
In terms of transportation, function is to provide easier, faster, and most of time safer option to get from destination A to B. When functions are reinstated, form can start to evolve from them.
Form/Shape/Color Form has to cooperate with function and follow, shape, organize according to the function of the object or system. After knowing what we want the object to do, we start to manipulate form into something that is most ergonomic and convent to use. Form has to provide basic understanding of what the object is and the function it embraced to. Form most of time has to meet expectation from user as to what it is, especially something that is for general public like public transportation. For example, when Segway first came out, many people didn’t know how to function it or what it is. But its wheels provide some sort of hint that this device transport people or objects around with hopefully faster and safer packages.
Cost For system or objects that are for public use, cost might somehow be more important than form because people can withstand the ugliness or dirtiness of a subway or bus to a higher degree than something they own themselves because they are only stay in the space for a relatively short period of time. For something that is privately own, cost is important but most of time form is more significant because that objects represent them, their taste, and their status. If I were designing a bike, maybe material is somewhat more vital than cost according to what my theme is.
Material/Impact on the Environment As designers, material choice should be consider at the top priority because the product hopefully will not going to just one person but will make a big impact. As the result, material for public transit should not only be durable, and easy to clean but also recyclable.