As I predicted some years ago, dual mode locomotives would become more prominent in r and d, and emerge. They are now the next big thing with rail head transport becoming more cost effective as companies produce scale to compete and road haulage becomes more expensive and slower.
Environmental Politics and economics play as large a part now in shaping the locomotive species as they did in 1955. Now with the emissions vogue for mid to high speed diesel power units things have changed. This means smaller space for the PU more space for scrubbing, but also the possibility for a return to the electro diesel and of course multi engine.
In the 1950's twin engines were chosen due to high power output relative to the available hydraulic and DE transmission systems which were then limited to about 2000 kw at a push in Germany, and for UK budgets and loading gauges, little over 1000 kw.
EE worked this one out in relation to getting "3000hp under the bonnet" for sustained 100mph express running, and the WR dedicated to light weight DH power by the early 1950s following the early adventures into heavier 1500-2000hp single engine units. Brush followed suite with the ugly duckling "Hawk" , which could have proven a swan in terms of performance at up to 3000hp compared to the castrated class 47. Even in the ashes of the deltic rose the phoenix of the uk's most successful passenger train, the HST with its high speed Valentas.
First the anglo belgian powered diesel hydraulic to raise eyebrows with its wheel slip free creep lifting enormous coal trains. Then we noticed the reverse, with old locomotives being refurbed sometimes reengined and sent out with new, smaller operators. Suddenly after the predominance of the GM/EMD v 12 two stroke mid speed whiner was under threat by the fragmentation of the industry and the nervousness over buying any loco which may be legislated out of traction wijthin its payback time
Now Bombardier shock us all with not two but four bustly little 750bhp units. This is a modular Traxx loco and they admit to hedging their bets by having a plan for battery replacing one or more power units.
This brings a lot of questions up. Firstly how often do you run on less than all units? Well deltics often ran the aberdeen route north of edinburgh on one unit, pairs of thirty sevens were often switched leading to control only. Another intention from the DB V200, the deltics to the HST was to allow for failure redundancy. This was often the case allowing the service to be completed even on time for the slacker diagrams. DMUs are generally
Secondly then you have all this on and off, which is bad news however. Larger diesel power units are high compression, long stroke and dual air charged, and the higher speed engines before in time did not respond to idle start stop in traffic.
Thirdly how much power do u really need to start a train? This is a major plus point for the next generation electro diesels which may only need to crawl from the rail head to the overhead AC wires. Here you can haul a thousand tonnes with one of those wee units in the new traxx without a gradient to ply. A class 37 first series once hauled a 1600 tonne dead train in south wales, the lower geared RA 7 version would have maybe done 2000 all be it at less than 20mph.
The next thing is back to longevity versus life cycle. I think it is pretty ridiculous to impose stingent and eventually zero emissions to frieght and express passenger given how many car and lorry journeys they replace. However the road lobby and the percieved need to have clear emissions limits on larger power units across the board means that some locos will maybe only have a 20 years life span and may be reengined or dual moded within that.
Historically rail operators have always tried to run powerunits at longer than manufacturers recommended service intervals and with rarer locomotives like the soveriegn class 60, they attempted to reduce intermidiary "examinations" as they call inspections and filter changes. Given low sales of this new traxx four PU or any other high speed engined loco, then they do not acheive a redundancy in servicing ie there are not enough powerunits spare or ready serviced to feed the small fleet. The pluss side is standard servicing at non rail depots though ,and if it comes to it, a cheaper replacement cost than a single v16 mid or high speed unit.
The future is a bit like 1955 if you ask me , a fragmented approach with some locos.trying hard to fix a political problem, orders being small and a some specialised to country or purpose, deisel electric or hydraulic , flirts with electro diesel, battery and alternatjive combustion. Fifth generation locos start to sound a lot like first generation fifties ones.