And I never pretended it to be fun
On a serious note, in such situations of course I prefer to take pics in slightly different positions (ideal option is when I can walk to another corner of course), but well, it just take the first car passing to place the filter (and most of the time you can judge without even a car to test it).
Then of course, at the ring the filter isn't always a good idea since it's often so bloody dark
As for myself, I am "working" on the highway these days since they are sunny enough to easily use the filter and still beeing able to go up to 1/200 (to be sure not to miss most cars). It's paying off because I got my first moving 959 for instance and quite a few nice cars.
In this case it's pretty easy to judge how to set the filter and I admit it's quite exciting to wait there and wonder what will come next
I'd like to shoot at 1/100 or even 1/80, but to be honest I prefer less "moving" sensation and ok pics rather than messing up an ultra rare car passing by, since Ihave just a single chance for each of them