Not exactly "what is the ideal diesel roster"; that could be a subject for another thread. From your railfan perspective, what is the ideal way for a railroad to dieselize?
To get the big question out of the way, let's ignore when dieselization takes place, in absolute terms at least.
Do you prefer when steam and diesels are bought/built alongside each other for some time (B&O, most national railways) or those where the first diesel comes after the last new steam (South Africa, N&W, C&O if you exclude PM)?
Should dieselization be fast (N&W, Clinchfield) or slow (extreme cases - Italy and Switzerland, ~50 years from last new steam to last steam operation. Even longer for some developing countries, ~60 years for Burma)?
In cases of overlapping orders and slow transition, it's common for the first diesels to be retired before the last steam. This even occurred with British Railways, though it's one of the fastest among national railways. In some cases (DB, China), the first diesels are retired while steam is still being built.
We're used to railways where passenger generally goes diesel earlier. What about railroads like GTW, which had no passenger diesels until the mid-50s? Or India and Poland, where most steam operation in the last years was passenger? N&W qualifies for both this and the opposite. First diesels mid-55, no passenger diesels until early 57, but no regular steam-hauled passenger after 1958, with remaining passenger steam downgraded, including streamlined steam still in that form on freights.
China ran out of dedicated passenger steam long before the end of steam, and pulled passenger trains behind freight steam afterward. East Germany was similar.
What should the last steam services be? Sporadic use of heavy modern steam on mainline freights (UP)? Sporadic use of heavy modern steam in helper service (ATSF)? Old steam on branches (Wabash)? Switchers (SP, N&W)? Road power as switchers, old (Japan) or newer (Zimbabwe)? Some manage regular mainline freight steam to the end (DB, South Africa, NKP).
If all the heaviest jobs are dieselized, should you keep older, lighter steam for the remaining ones or use overqualified modern steam (NdeM 4-8-4s on locals)? In a similar fashion, though there was mainline freight service to the end, South Africa retired its last dedicated steam switchers around 1986. Switching by 4-8-2 tender engines - overqualified and inappropriate switchers by any standards - was already common, and it only increased. Even 4-8-4s were seen as switchers in their last years.
Should older steam go first (N&W, China, India) or should most types last near the end (CN, CP, British Railways)? There are some railways where it seems at first glance like most major classes last near the end until you remember that all newer/larger classes were made in smaller numbers and vanished early (PRR, DB).
What about major rebuilds of steam after the last new steam? DR is the best-known example.
Some railroads bought used steam after their last new steam, NdeM and DM&IR being familiar cases. In the Missabe case, this was before their first diesels. With Mexico, it was after.
Zimbabwe is famous for its unusual case of reversion to steam. Guatemala, Ecuador and some small railways and industrial operators are similar, though. The usual reason is inability to maintain diesels. Clearly not perfect from a management perspective, or for anyone who likes to see plans carried out.
Do you like to see periods of experimentation (most national railways, British Railways being a famous case) or getting it right the first time (most railroads that dieselized with a single generation of power: N&W again, DM&IR, Wabash)?
Note the assumption in several of these questions, that the newer steam is larger and/or faster. This is not true everywhere. Possible dieselization is influenced by what the steam fleet contains and what services it must perform. Sometimes, for example, there is a need for power to fill new services. In India, diesels were assigned to new trains, faster than any regular steam trains (it helped that India had no true expresses to begin with). In China, famously, the average length of passenger trains increased during the transition era. Until enough diesels were available, this meant an increasing number of passenger trains needed high-tractive-effort freight power, which slowed their schedules.
I have opinions on some of these, but I won't say anything until some of you have.
To get the big question out of the way, let's ignore when dieselization takes place, in absolute terms at least.
Do you prefer when steam and diesels are bought/built alongside each other for some time (B&O, most national railways) or those where the first diesel comes after the last new steam (South Africa, N&W, C&O if you exclude PM)?
Should dieselization be fast (N&W, Clinchfield) or slow (extreme cases - Italy and Switzerland, ~50 years from last new steam to last steam operation. Even longer for some developing countries, ~60 years for Burma)?
In cases of overlapping orders and slow transition, it's common for the first diesels to be retired before the last steam. This even occurred with British Railways, though it's one of the fastest among national railways. In some cases (DB, China), the first diesels are retired while steam is still being built.
We're used to railways where passenger generally goes diesel earlier. What about railroads like GTW, which had no passenger diesels until the mid-50s? Or India and Poland, where most steam operation in the last years was passenger? N&W qualifies for both this and the opposite. First diesels mid-55, no passenger diesels until early 57, but no regular steam-hauled passenger after 1958, with remaining passenger steam downgraded, including streamlined steam still in that form on freights.
China ran out of dedicated passenger steam long before the end of steam, and pulled passenger trains behind freight steam afterward. East Germany was similar.
What should the last steam services be? Sporadic use of heavy modern steam on mainline freights (UP)? Sporadic use of heavy modern steam in helper service (ATSF)? Old steam on branches (Wabash)? Switchers (SP, N&W)? Road power as switchers, old (Japan) or newer (Zimbabwe)? Some manage regular mainline freight steam to the end (DB, South Africa, NKP).
If all the heaviest jobs are dieselized, should you keep older, lighter steam for the remaining ones or use overqualified modern steam (NdeM 4-8-4s on locals)? In a similar fashion, though there was mainline freight service to the end, South Africa retired its last dedicated steam switchers around 1986. Switching by 4-8-2 tender engines - overqualified and inappropriate switchers by any standards - was already common, and it only increased. Even 4-8-4s were seen as switchers in their last years.
Should older steam go first (N&W, China, India) or should most types last near the end (CN, CP, British Railways)? There are some railways where it seems at first glance like most major classes last near the end until you remember that all newer/larger classes were made in smaller numbers and vanished early (PRR, DB).
What about major rebuilds of steam after the last new steam? DR is the best-known example.
Some railroads bought used steam after their last new steam, NdeM and DM&IR being familiar cases. In the Missabe case, this was before their first diesels. With Mexico, it was after.
Zimbabwe is famous for its unusual case of reversion to steam. Guatemala, Ecuador and some small railways and industrial operators are similar, though. The usual reason is inability to maintain diesels. Clearly not perfect from a management perspective, or for anyone who likes to see plans carried out.
Do you like to see periods of experimentation (most national railways, British Railways being a famous case) or getting it right the first time (most railroads that dieselized with a single generation of power: N&W again, DM&IR, Wabash)?
Note the assumption in several of these questions, that the newer steam is larger and/or faster. This is not true everywhere. Possible dieselization is influenced by what the steam fleet contains and what services it must perform. Sometimes, for example, there is a need for power to fill new services. In India, diesels were assigned to new trains, faster than any regular steam trains (it helped that India had no true expresses to begin with). In China, famously, the average length of passenger trains increased during the transition era. Until enough diesels were available, this meant an increasing number of passenger trains needed high-tractive-effort freight power, which slowed their schedules.
I have opinions on some of these, but I won't say anything until some of you have.
