Why is the Class 68 so long?

[whhistle]

As the power output increases, the cooling system gets larger, you need a larger fuel tank (to maintain the same range when using the extra power), AC traction drives need more space for the inverters etc. etc.

Also meeting modern emissions rules has slowly increased the size and complexity of cooling systems (to allow tighter control of temperatures in different parts of the engine). Just compare the size of the radiators - and the rest of the loco - for a 1970's US EMD SD40-2:

BNSF 6371 EMD SD40-2 [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0 )], by terry cantrell (originally posted to Flickr as BNSF 6371), from Wikimedia Commons

...with a modern EMD SD70ACe - and the latest Tier-4 locos have even larger cooling systems. The picture below is an SD-70ACe at the front and an older SD70MAC at the back.

BNSF 8794 Lincoln, NE 10-19-14 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0 )], by Augy8400, from Wikimedia Commons

This is a side view of the (massive-looking, Tier-4 compliant) SD70ACe-T4 https://commons.wikimedia.org/wiki/File:UP3053SD70ACe-T4.png

Shows how boring Diesel in the US is.
At least ours are significantly different shapes and mroe interesting to look at :P

 

[ac6000cw]

At least ours are significantly different shapes and mroe interesting to look at :P

Really?

In regular use, in the UK we've got down to:

Three types of passenger/mixed-traffic diesel - 57, 67 & 68 - 'box on wheels' dual-cab design.

Three types of freight diesel - 56, 66 & 70 - two 'boxes on wheels', the other a dual-cab-plus-hood design.

Then there are the old oddments (living on borrowed time) - 20, 31, 37, 47 - two of those are 'box on wheels' dual-cab designs.

I can think of at least eleven variations of passenger diesel alone in the US (from four different manufacturers) in regular use - (EMD) F40, F59PH, F59PHI, F125, (GE) P32-8, P32AC, P42, (Wabtec/MPI) MP36, MP40, HSP46, (Siemens) SC44 'Charger' - plus myriad variations of freight diesels, depending on how far back into older loco designs and rebuilds you want to go...

If you think the US diesel scene is less interesting than ours, you haven't been there (or explored much if you have).