Hi julian,
To do this you would need to use a 10stop filter, allowing you to do exposures of 30 seconds or more, You would probably need to adjust your white balance to a custom setting unless you have plenty of cash for the Lee Big Stoppa.. £94.00 plus the holder.
You could go to ISO100 f18-22 and probably get 1/60 on a bright day and slightly less with a polariser fitted.
Or you can stank 3 3stop ND filters (not graduated)
Although during the day you will get some subtle smuges to slight blurring of moving cars..
The rick is the amount of light on the cars, with a shot taken at night it is the brightest part that the camera records (the lights)...
A bit of experimentation with shutter speeds until you get the desired effect will be needed...