PC: Special loads in employee timetables

[Jerry Jordak <jer@xxxxxxxxxxxxx>]

I asked this over on the PRR-Talk list, and apparently several hundred 
Pennsy fans didn't have an answer, so I thought maybe a couple hundred 
Penn Central fans might be able to do better:

Most of my PRR and PC employee timetables have a section titled "Engines 
and Special Load Restrictions," section 1160-A1. There is a chart 
listing various tracks, followed by five columns titled "class of 
engines" numbered 1-5, and four more columns titled "special loads" with 
letters L, M, I, and J. These columns then have letters or numbers in 
them to designate if/how these locomotives or cars are restricted in 
operating on the listed tracks.

The numbered columns for "class of engines" list different classes of 
locomotives in each column, so a train crew can tell if their locomotive 
could operate on a given section of track. However, the "special loads" 
sections have no other description in them other than the letters.

What I'm wondering is: what kind of special loads do L, M, I, and J 
stand for?

Thanks,
-JWJ