
fortunately and because the work of smart people you can get tools around there how will make your life easier.
If you use XSI ( like me ) or maya even 3ds max go see here.
This is the page for RoadKill plugin for XSI , from there you can go grab this unwrapper
for maya , max or use as stand alone version.
This is pretty powerfull and simple to use , integrate well in XSI worflow, and best of all It's FREE !!
So worth trying it