One of the issues that will come up in these projects is local variation. There will be differences on a state-by-state basis, and unique things within a jurisdiction. The only way we're going to learn about these is by pushing forward, but we can think about them in advance so that there's a plan.
Each time a new department or company is brought into the process, there will be a discovery period. Local statutes and policies will need to be figured out. There will be important items that are not necessarily appropriate as data for OSM. Thus, we will have the local policy file.
I don't know what form this will take yet. I'm on a learning curve with mkgmap. I don't think there's an "emergency" mode for a Nuvi, and there are multiple classes of emergency vehicle. An ambulance is not a police car, is not a pumper, is not a hook-and-ladder truck, is not an extensible ladder truck. Each different class of equipment may have a different set of routing constraints. Some of these constraints can be configured using traditional OSM tagging (maxweight, maxheight, maxlength), but others may reflect specialized local knowledge. We are very likely going to end up with different maps for different equipment classes.
We also must incorporate specific local knowledge. The local responders may be able to tell us that certain routes should not be taken if at all possible. We will need a way to describe that and get it into the GPS of choice.
Now, and this is IMPORTANT: The primary application for this is not for a particular engine company or volunteer district responding in their own territory. The primary application is a mutual assistance call, where, say, the McKownville VFD receives a request for assistance from the neighboring Westmere VFD and needs to go somewhere they ordinarily don't. Whenever I describe the project to someone involved in the real world of firefighting, they invariably bring this issue up without any prompting on my part. Out of area response weighs heavily on the minds of firefighters.
So there's one of the key areas that needs to be fleshed out -- how do we reflect local policy? Right now, I'm interested in ideas and approaches, not code. It's not time for code just yet. Have at it in the comments.
