The Transportation Research Board – the TRB recently announced the continuation of a research project with the Univ. of Akron, Ohio that is looking into the use of LiDAR to identify highway vehicles at speed. They will study the use of a mobile system that can collect data at highway speed or be parked in a location for a couple of hours. The current systems are mounted in the pavement and provide limited information.
The real challenge, as you might have guessed is in the software to automatically identify the vehicles. They refer to shape based classification and the need to determine the number of axles per vehicle as being part of the research. Given the narrow scope of interest it seems like this could be an area where progress can be made.