Real-time image analysis is always CPU intensive but there are many ways to reduce the load. First of all, that GPU could probably be put to good use. Try changing the settings in the parameter file in order to use the GPU instead and see if that changes the CPU usage.
Also, both the fps (frames per second) and resolution of the camera greatly affect the number of computations per second. If you can set the resolution of the camera to be lower (or change the settings to downgrade the incoming data stream before analysis) and also lower the fps, you should see a strong reduction in CPU load. I had a CPU fan failure on a device, but was still able to use it and reduce the CPU load to almost nothing when I reduced the fps to two frames per second. Unless you are looking at a very tight angle and the vehicles are passing by at very high velocity, you probably do not need a high framerate.