Hm. I checked and the crossing in question is here. There is a gentle S curve to the south-west, so I estimate a line of sight on (left-driving) trains from London of 600 m from the north-west side of the tracks, or 15 seconds at the line speed of 90 mph. To the north-east, there is another curve and I estimate a line of sight of 400 m from the south-east side of the tracks, that's 10 seconds. I also found this FoI request, and photos of the crossing are included on pages 26-30 of "Area Docs Part 2.pdf".

As for what exactly Network Rail sees as a problem, although I blame the Brentwood Gazette journalists for being lazy in reporting their communication in full, it is confusing. In its first longer letter (pages 12-13 in "Area Docs Part 2.pdf"), they refer to high train frequency, and "sighting" that is 27% of the required in one direction and 79% in the other, and say neither whistles (residential area) nor mini traffic lights (station area, more than two tracks) are a possible mitigation and trains would have to be slowed to 25 mph. In a letter on page 8 of "Area Docs Part 1.pdf", however, Network Rail says that one of the three tracks is a siding used by freight trains, which on occasion blocked the footpath, and pedestrians have been walking around the freight trains, thus extending the time they spent in the danger area. (The use of the track by long freight trains is vehemently denied by a protesting local.) However, in another letter on page 36 of "Area Docs Part 2.pdf", Network Rail says that the problem they see is the curvature of the line alone and not foliage or misuse of the crossing. It appears however that three tracks (as opposed to two or one) are a problem.

Even if Network Rail is right, they didn't explain themselves properly on the outset even to the local council (much less the locals) and when the local council denied their initial request for closure, they went one level higher to get it.

The fact that Network Rail waited two years (and further protests) until the actual decision to build the tunnel is also a scandal, though at least it contradicts the hypothesis that the whole affair was a corrupt deal to give an over-priced contract for unnecessary infrastructure to a contractor.

_{*Lunatic*, n.
One whose delusions are out of fashion.}