It is not ever 'just'. This isn't copying code. This isn't building identical silicon for multiple end users. This is more like trying to add additional threads to something that is not embarrassingly parallel. What you're saying is like saying 'why can't you just make all of my computer programs run on all 32 of my CPU cores?'.
And even if you minimise the increasing complexity added by expanding the system, waterfall-style design (which is absolutely the most appropriate approach when dealing with these sorts of projects) front-end loads a frankly Herculean amount of risk management into the process because you want to make sure that's all absolutely square and true before you progress to implementation.
Lastly, it's worth noting that with systems this complex, a lot of the detail is bespoke because the number of complicating input variables the system is exposed to necessarily requires a relatively bespoke solution. Yes, the idea of e.g. ETCS being ETCS is going to hold, but how that works in reality, how it ties in to all of the other legacy systems, etc. will mean that you can't for example just take ETCS-equipped train A and and drop it into ETCS-equipped network B.
I was thinking that only the track sensors and traffic lights along the way need to be upgraded and the drivers would just drive trains as usual and they would be sequenced on a shorter distance/time between trains. I forgot that trains also have to be connected to the new system.
It is not ever 'just'. This isn't copying code. This isn't building identical silicon for multiple end users. This is more like trying to add additional threads to something that is not embarrassingly parallel. What you're saying is like saying 'why can't you just make all of my computer programs run on all 32 of my CPU cores?'.
And even if you minimise the increasing complexity added by expanding the system, waterfall-style design (which is absolutely the most appropriate approach when dealing with these sorts of projects) front-end loads a frankly Herculean amount of risk management into the process because you want to make sure that's all absolutely square and true before you progress to implementation.
Lastly, it's worth noting that with systems this complex, a lot of the detail is bespoke because the number of complicating input variables the system is exposed to necessarily requires a relatively bespoke solution. Yes, the idea of e.g. ETCS being ETCS is going to hold, but how that works in reality, how it ties in to all of the other legacy systems, etc. will mean that you can't for example just take ETCS-equipped train A and and drop it into ETCS-equipped network B.