Hi SEOAspirant,
The truth is, Google does not have published guidelines for businesses with models like yours. Because of this, you must view some of the following in the light of an experiment rather than an accepted practice.
Typically, for SABs (service area businesses) one is dealing with something like a plumbing company located in city A, but serving cities A, B, C and D. In such cases, the guidelines are clear. You create a single listing for the location, hide the address and choose a service radius or, in the new Google Places for Business Dashboard, select a couple of service cities. You never create additional listings for the service cities.
Your business model is more complex, however, as it appears that you have a location in San Diego but that your employees offer services nation-wide. I'm not very familiar with the auto transport industry, but I'm presuming this means your drivers deliver cars to dealerships or individuals all over the country, and have face-to-face transactions with the recipients. If so, I think there are 3 possible paths open to you.
Path 1:
This is in line with Stephanie's comment. In some cases, business models like yours will establish a representative in a target city and use the home address and phone number of that person. *Note that you must not use a toll free or re-directing phone number. The representative of your business in that city must be the one who answers the phone there, at the location. And, the number he/she uses must not be shared with any other business. For example if the driver shares his home with his wife who runs an accountancy firm out of their home, they cannot share the phone number.
The possible downside to this is that Google is quite capable of seeing that the address you've listed is a home. Google is fine with home based businesses, at this point, but it is not impossible that in the future they might decide that national businesses who have taken this path of using a home address to establish a location in multiple target cities are gaming the system. Tons of businesses currently operate this way and, from what I have seen, appear to be surviving in the system, but I would not rule out the concept that Google might decide they don't like this at some point.
Path 2:
This is in more line with Ian's comment, with some slight refinements. In this scenario, your national business realizes that you must invest in a small office in your main target cities and staff that office with someone who answers calls and takes orders from clients. This scenario is completely without a downside, because you are then like any other truly local business with a clearly accepted physical location in each of your target cities. You can proceed as any local business would, without fear of reproach.
What you should not do is attempt to get a virtual office, P.O. box or any similar faux location in your target cities. This is a shortcut attempted by many businesses with models similar to yours and it risks penalties and worse.
Path 3:
You decide you can't yet afford to accomplish the Path 2 plan. In that case, you could determine to set up a single listing for your single physical location and determine that this is the sum of your local efforts for now. Beyond establishing this, you determine to go after high organic visibility in your service cities via a combination of content development, linkbuilding and other traditional organic SEO practices. In this scenario, you are hoping to achieve high organic rankings for a wide number of cities, but are not going after LOCAL rankings due to a lack of legit physical locations. This is a completely risk-free path as well. In future, should you develop funding to open new offices in new cities, then you can begin to follow Path 2.
Long answer, I know, but your scenario is deserved of very careful consideration before you proceed. Hope this helps!