Only "slim-line jets" are used on the landscaped layout, to prevent major destruction. Since there are no long straights, just lots of 6", 9" & 15" curves, intersections, RXR's, bridges and loops...the slimmies are speedy enough. Of course the train sometimes catches careless "rally-racers" and rams them into the nearest structure which creates some hilarious "wedgies". Nothing ever gets destroyed so bad it can't be easily fixed (so far).That's pretty cool! I bet you have to watch out for "Flying Cars" on that layout! One could really wipe out a lot of detail.
You could be seeing dust, or the grey paint I am using to keep the L&J track from standing out (as much)as "toy" track. I do occasionally dust off a few roofs and vehicles, remove cobwebs from light-poles, etc, but I suppose I usually just let the cars "dust the track". It's been about 9 years since I screwed down this 50 yr old track in my basement and it always "fires" right-up and operates perfectly. "Spot" rail cleaning is very minimal, the train rails require more attention than the slot rails. I think it might be that I consider "dust" to be just added detail, but I promise you that when I see the first tumbleweed (maybe the 2nd), I'll get to dust'n.Great looking L&J track. Looks like it needs a little dusting