What this line should have got are tramtrains, a passing loop and a few extra halts - at Brentwood Road near to Romford and Wingletye Lane near to Upminster. The shorter length of the tramtrains would have meant that shorter platforms would need building whilst being tramtrains the rolling stock could use the 25kV power supply. The more frequent service and extra stops would have boosted patronage and helped reduce road traffic.
At least however the line survived and now has a future - unlike quite a few other branch lines here in London. Simon
There was a passing loop at Emerson Park formerly, but that's long gone. Also, nearly all of that line is in a cutting and building halts would be difficult in terms of excavation.
I suppose Southminster and Braintree qualified under cheapo electrification to get rid of DMUs, too. Curious to see how these runts survived -- and prospered (who'd have thought of 12 car direct trains LV-Braintree 50 years ago) when others, more sound, died on the vine (eg St Ives, Maldon, Northern Heights, Palace Gates, Aldeburgh... all of which would be used now). I remember being the only passenger from Romford to Grays changing at Upminster one winter day in 1965, when closure was thought round the corner, with the DMU, less than 10 years old, belching black smoke!
Witham - Braintree survived mainly due to the efforts of the local MP at the time, whereas the same could not be said for Witham - Maldon. Maldon could do with a train service nowadays.
There were many anomalies during the Beeching era. Village stations such as White Notley (on the Braintree branch) survived, whereas a large and developing town such as Haverhill in Suffolk lost its service.
Quite agree re Haverhill ( a viable branch would have been Audley End-Bartlow-Haverhill) but I'm not so sure about the reason for the survival of Braintree. As far as I remember, Maldon and Braintree were both in the same constituency at the time!
From memory (either a conversation with rail historian or from a book) the Braintree branch was kept in operation because of plans in the 1960s to make Stansted a London Airport. BAA took over the airport in 1966 and started flights from there soon after. At the time a number of schemes were mooted including reopening the Braintree to Bishops Stortford line to passenger trains (which had ceased in the 50s) and running a Stansted Airport service between Witham and Harlow. It certainly makes sense as BAA held significant political sway back then.
In the end the Stansted project was delayed until the 80's, a dualed A120 was built along the base of the disused line as part of a now-shelved project to provide a motorway standard road from the M11 to Harwich.