Pennsylvania Railroad locomotive numbering

Most other railroads numbered their locomotives in logical sequences, so that from hearing a locomotive's number one could deduce with some approximation what type of locomotive it was. An example would be the New York Central; 4-8-4 Niagaras were in the 6000s, 4-8-2 Mohawks were from 2700-3200, 4-6-4 Hudsons were 5200-5500, and so forth. Not so the Pennsylvania Railroad. Paradoxically, the Standard Railroad of the World, so in love with standardization and order elsewhere, with its 600-odd identical Decapods, 525 identical K4s Pacifics, and all the rest of its standard and uniform fleet of locomotives, assigned locomotive numbers completely at random.

Oh, later on some blocks of sequentially numbered locomotives did emerge, with P5 electrics in the 4700s, GG1 electrics in the 4800s, the Baldwin-built K4s series between 5400-5499, T1 4-4-4-4 duplex express locomotives in the 5500s, other duplex locomotives in the 6100s, M1 4-8-2 Mountains in 6700-6999, and a few others. Otherwise, chaos ruled.

The reason for this? Firstly, the sheer number of locomotives the PRR owned, at one time nearly 8000, meant it was hard to keep blocks of numbers free for a new class. Secondly, the PRR initially divided its four-digit number range into segments for different divisions, making the job even harder. Thirdly may indeed simply have been that the PRR's cast smokebox front number plates -- plain circles for freight locomotives but keystones for passenger -- made renumbering difficult, since a new casting would have to be made, by hand, for each.

Few locomotive numbers on the PRR were unique to one locomotive; rather, when one was taken out of service, its number would be re-used on a new locomotive.

As an example, the first ten locomotive numbers, circa late 1930s:

1. Class H6b Consolidation (2-8-0)
2. Class L1s Mikado (2-8-2)
3. Class B6sa switcher (0-6-0)
4. Class H6a Consolidation (2-8-0)
5. Class H6 Consolidation (2-8-0)
6. Class D16sb American (4-4-0)
7. Class H9s Consolidation (2-8-0)
8. Class K4s Pacific (4-6-2)
9. Class H6a Consolidation (2-8-0)
10. Class E3d Atlantic (4-4-2)

The preponderance of Consolidations is simply down to them being the most common type on the railroad.