Trip passes were issued by all RR’s and provided to employees of other railroads, usually just for “official” business.  If you were traveling on personal business/vacation and weren’t eligible for a trip pass, you could get a half-rate order (i.e., the foreign road would charge you one-half of the regular rate; Pullman accommodations had to be paid in full).

I (and my wife) did a LOT of traveling on half-rate orders all over the US when I was on military leave from the LIRR.  When I was actively working and carrying my LIRR pass, most (not all) foreign conductors would honor the LIRR pass for a coach ride.  My best “score” on that account was a free ride on the Erie-Lackawanna from Hoboken to Chicago on the Lake Cities.  Lots of trips on PRR name trains from NY to Philadelphia.  PRSL and the IC would NEVER take my pass. Archive/Info: Brad Phillips

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Trip Pass Carpenter NY to Yaphank 11/1921
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Trip Pass Trainman Sag Harbor to Jamaica 12/1928
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Trip Pass Trainman Sag Harbor to Jamaica 12/1928
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Trip Pass Block Operator Jamaica to NY 7/1930
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Trip Pass Highway Watchman  Stuart Manor to Jamaica 12/1934
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Trip Pass Extra Clerk over entire system 1936
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PRR Trip Pass for retired LIRR Engineman over entire system 1943
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Trip Pass for daughters of ticket clerk Patchogue to NY 10/1953 Archive: Dave Keller
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Trip Pass UP RR Livestock Agent  - Port Jefferson to NY 5/1950
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Trip Pass UP RR Livestock Agent  - NY to Port Jefferson 5/1950
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Trip Pass Agent "20 years of service" 
entire system 1955-56
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Trip Pass Wife of Agent "20 years of service" entire system 1955-56
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Trip Pass lifetime - retired engineer  
Dashing Dan
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Trip Pass lifetime - Wife of retired engineer  Dashing Dan

Retired LIRR Ticket Clerk Thomas Bayles took me on a coach trip to Bridgeport, CT about 1967 or 68. He carried me on his LIRR pass into Penn Station and when we got our connection from GCT on the New Haven, he had the option to show the conductor either his LIRR pass or his Pennsy pass, which he was also issued. 

He opted to show his LIRR pass and we got to ride free.  The conductor said to him "Good thing you didn't show me a Pennsy pass. . I'd have thrown you off the train." Obviously the conductor wasn't afforded a free ride on the Pennsy sometime back using his New Haven pass. . . . and he was about to return the favor. Info: Dave Keller