@Gemma βοΈπ°πΊπΈ π΅π π @Not Just Bikes π³π± @Ati the marginal cost of adding an extra car could be very low, or it could be extremely high, depending on whether the trains that are running are already at the maximum length for the stations they serve.
And adding one extra train may be extremely expensive when an area is already running at capacity.
And anyway it would be one less extra car / train for other passengers.
Of course it depends on the time of the day: on the commuters' trains around Milan bicycles are usually allowed, trains have room for them etc. and usually are not an issue, but they are not allowed during rush hour, when close to Milan trains tend to be already filled to the brim with standing people. (and of course at that hour the system in that area is already running at capacity, with trains that are as long as possible and as frequent as possibile)