Restriction of US currency supply meant that the Victorian Railways could not buy all the US diesel-electric locomotives that it wanted. The much easier availability of UK currency meant that British electric locomotives were an easier purchase to make, helping tip the balance in favour of electrifying the Gippsland line.
Weren't some diesel trains made in the UK?
Briquette traffic on the Gippsland line was year-round, high volume traffic that went to destinations in suburban Melbourne that were already electrified such as Newport Power Station and the Heinz factory in Dandenong. This freight justified electrification out to the Latrobe Valley.
But it somehow didn't justify level crossing removal, obviously a lack of foresight.
In the case of the Darling-Glen Waverley extension, the VR was building a suburban electric railway from scratch, allowing them to use steeper grades and avoid the construction of level crossings.
Caulfield-Dandenong was opened before the first ever internal combustion engine car was built.
But there were horse drawn road vehicles, so there was still some road traffic.
You're making a mighty big assumption that the VR cared about road traffic congestion around level crossings.
Regardless of whether the rail operators cared about road traffic congestion, they would have cared about the cost of employing a gatekeeper to operate the gates, which, being ongoing, adds up over time.
I gather that the roads were there first and the railways were built across them later, surely VR was opposed the new roads being built across existing railways, just as they were opposed to tram/train level crossings.
If a railway operator builds a new railway across an existing road on the same level, don't you think they would only be allowed to do so on the condition that there is some limit to train frequency?
As for the crossings of the time, the gates had to be swung round, closing off the road a certain amount of time before the train arrived at the crossing. You simply must have train headways much longer than the interval between swinging round the gates and the train arriving at the crossing.
In those days, the signalmen and gatekeepers had to each wait for a gap in the traffic before swinging round the gates, thus needing to anticipate the train's approach much further in advance than the automatic block signalling does today.
As far as I know the crossings in the suburban area worked as follows; when a suburban train arrived at one station, every set of swing gates before the next station were swung round, and the wicket gates locked, before the train departed.
If you try to run 20 tph over a swing gate level crossing during the busiest times, the crossing would be closed for the whole of every peak period. Doesn't sound very realistic.
I read what you wrote above, and I know they didn't run trains that frequently over the crossing, but that limit would still have been there, it's just they the train frequency at the time would have been under that limit.
Now I know that rail traffic along the corridor dropped off shortly before the catenary was cut back. But might have it remained higher if all level crossings between Calufield and Dandenong been grade separated by then, if they had, surely more freight would have gone by rail.
I checked the timetables page, which I haven't seen before, but research can be a challenge, it's not clear whether it's referring to the passenger trains or also freight trains.
I assumed you already know the trains frequencies, having done the research previously, but it's best you either answer or allow someone else to do so, I'm not asking anyone to do any research here, I'm just anticipating that someone here already knows, even if it isn't you.