bramling
Veteran Member
2V90, the 1758 London Kings Cross to Welwyn Garden City was increased to 8 cars when the class 321s arrived with FCC - around 2009. Until that time, the equivalent train stopped at New Barnet but not Hadley Wood (all the other XX:28, XX:58 King's Cross to Welwyn Garden City formed of either a single 4 car unit or 2 x 3 car class 313s continued to serve New Barnet). The reason given at the time was that 8 car trains could not serve platform 4 at New Barnet, although I can remember an extended stop at platform 3 at New Barnet while aboard an 8 car class 365 while a Person Under a Train incident further north was sorted out. 2V90 does not use SDO at Hadley Wood platform 4.
I do not know why New Barnet requires SDO, the physical platforms do appear long enough for 8 cars, however 8 car trains southbound formed of 2 x class 387, such as 2Y87, the 08:44 Welwyn Garden City to King's Cross cut out the doors in the 7th and 8th car, though this train was previously formed of pairs of 317s, 321s or 365s and these did not cut any doors out.
The issue with New Barnet down platform might be to do with the signal berth being tight, as immediately north of the platform is a crossover DS to DF, and the signal is very close to the platform IIRC.
Going back to the 90s, all of these services were KX to Letchworth at XX22 and XX52, and all were 2x313, except 1652 KX to Letchworth which was 1x317, although latterly became 1x365. With the “seats for you” timetable all these services were axed, the paths being used for the extra XX23 and XX53 KX to Royston fast services and today’s XX28 and XX58 to Welwyn only. The 1654 KX to Cambridge seems to be an exception to the rule.