Why do the railroads have so many different varieties of covered hoppers?

[Junctionfan]

I was looking at some freight car rosters of CN and CP. Good lord do they have a lot. CN has tons of those cylindrical hoppers in CN, CNA, CNIS and CNLX reporting marks. They have 3 bay centerflows, 54 PS hopper (3bay), they have something called a slab hopper, they have a good few Procor pressure flow hoppers, and they have a few others.

Why do the railroads have so many different ones that are even duplicate of what commodity they are moving?

Other interesting notes is that NS is the only railroad to my knowledge that owns Trinity power flow hoppers. CSX has several varieties of 2 bay covered hoppers and of course others too.

Note that I am only talking about the ones that are in the railroad reporting mark and not ones bought through the aquiring of another railroad.

[dehusman]

Different commodities, different characteristics, different manufacturers, cars bought at different times, some cars bought, some cars leased.

Dave H.

[Junctionfan]

I think the CNLX cars are leased. What other leased cars do the class 1s uses still with their reporting marks on them covered hopper wise?

[BaltACD]

Different commodities with differing flow characteristics and differing weight per cube.

Heavy commondities such as cement require a 'small' cubic capacity to reach the maximum permitted weight on rail.

Lighter commodities such as grain require 'large' cubic capacities to reach the maximum permitted weight on rail.

Other commodities fall somewhere between these two. Certain commodities also have 'flow' problems and thus the 'air slide' variant of covered hopper was developed to assist in the unloading of the car.

[Junctionfan]

I have seen cement in 56 cylindrical hoppers. I saw one leased to Inland Cement with CGLX reporting marks.

[Anonymous]

Go through your town and look at each Fire hydrant- you'll have some more Square, some Circular- oval, oblong shaped-

A year produced A certain type, then a newer model came out, then perhaps one year they made these terribly bulky ones, followed by next year meaking a brand new one

So each year has a different production.