Those are definitely good reasons especially the speed limits. Having any 100 MPH train slowed following a 62 - 65 MPH train would really gum up the works, Are the slower cars assigned to isolated lines as much as possible to prevent this happening?
No. Many named old LD trains still have ICF rakes (consists). There are even a few hybrid ICF rakes with air braked ICF coaches, like the venerable Howrah-Delhi-Kalka Mail, now called Netaji Express, even though it still carries mail.
Daughter has a long business trip there. Can you give a thumbnail spotting way for her to avoid the vacuum braked car trains? Would riding just AC cars help?
All of the Rajdhani, Duronto, Shatabdi, Jan Shatabdi, Vande Bharat, Amrit Bharat, Humsafar, Tejas, Garib Rath and a couple of other classes of trains are LHB. The old named trains are about two thirds LHB and a third ICF with trains getting transitioned progressively. Additionally generally any train that has a Cream and Maroon (Utkrisht) livery or the classic light and dark Blue livery is ICF, and Red and Grey livery or Sky Blue (AC Day Coach) livery is LHB. Best way to verify is to get the train number and plug it into the search field of the following web page:
https://indiarailinfo.com/trains
It will bring up your train. Click on the line showing your train, and on the page that comes up look near the bottom where the consist layout and equipment type (Rake - LHB or ICF) is shown. For example for 12302 (New Delhi - Howrah Rajdhani Express via Grand Chord) it shows:
OTOH for 12312 (Kalka - Delhi Jn. - Howrah Netaji Express) it shows:
Notice the "Rake" information in each. That is the most reliable way to check what is actually operating at present.
The Coach identifiers appear exactly the same way on the ticket. The letter(s) in them identify the type of coach. Here is an explanation of only those that appear in the diagrams above. There are about half a dozen other types of coaches not listed here.
S - Non AC 3 Tier Sleeper
GS - Unreserved Non AC Sitting accommodation
H - AC First
A - AC 2 Tier Sleeper
B - AC 3 Tier Sleeper
HA - AC First and 2 Tier Combo
PC - AC Pantry Car/Hot Buffet Car
EOG - Generator/Luggage/Guard
SLR - non-AC Seats/Luggage/Guard
HCP - High Capacity Parcel
L - Locomotive (on these trains a single 6200HP WAP-7)
Notice that Rajdhani is fully AC whereas Netaji is mostly non-AC. Also notice that both trains carry an entire car of Parcel and Mail - the HCP. Also, the discerning will notice that the Rajdhani has End/Head on Power Generation (HEP power) whereas the Netaji consists of self-generating Coaches with axle driven Alternators charging banks of Batteries in each coach, with the alternator/rectifier/batteries/inverters powering the individual coaches.
So this would be the end of vacuum brakes in India? Or are they still in use on freight, thus requiring the continued use and procurement of dual-braked locomotives?
They have many years to go before the transition is complete on both the passenger and freight side. All new equipment is air braked. Some ICF coaches have been converted to air braked. New locomotives are no longer equipped with Vacuum brakes.
What about the neighboring countries to which India presently runs or might one day run thru trains? Not that any one-sided changes in standards might preclude such thru running?
The exchange pool is distinct from the general equipment within the country so as long as the interchange pool works in both countries all is good.
There is no rail equipment flow between India and Pakistan at present and is unlikely to be resumed anytime soon. Between India and Bangladesh and India and Nepal all cross border equipment is of the latest generation LHB type (Bangladesh has about a hundred LHB Coaches and just ordered 200 more), Within Nepal everything is new.
Within Bangladesh the situation is same as in India, but probably a few years behind. In addition to assorted classic ex Pakistan Railway equipment, they have more modern air braked equipment from PT Inka (Phillipines) and CRRC (China) and RITES (India) But that has no impact on what happens in India and vice versa since what crosses the border is all new air braked LHB cars. On the freight side also only air braked equipment cross the border, though Bangladesh is adequately equipped with dual braked and dual coupler locomotives just like India. Additionally more than half of Bangladesh Railway is dual gauge (Broad and Meter), and of the remaining half, half is Broad (West) and the other half Meter Gauge (East).