Third rail extension

While I would prefer to see the North Downs rail route between Reading and Gatwick fully electrified, instead of the 50% DC third rail as at present, I am pleased that Great Western Railway is looking at leasing a fleet of refurbished Class 761 ‘Flex’ train sets on this route.

One snag I can foresee is the gradients presented to the trains in crossing the North Downs, particularly with the diesel engines and fuel tanks adding extra tonnage to the train weight. There is also the effect of acceleration from stations and after speed restrictions.

Could this be mitigated by extending the third rail for half a mile or so, to assist trains leaving stations where third rail supply already exists - for example, eastbound at Wokingham and Shalford Junction and approaching Reigate, where trains have to run uphill to the station?

For westbound trains, the third rail from Guildford terminates at Aldershot South Junction but is followed by an adverse gradient.

There are two locations where the North Downs line is close to other electrified lines. At Dorking it crosses the electrified South Western Railway line. Trains travelling west from Dorking face a four-mile uphill gradient to Gomshall. Would it be feasible and economic to take a DC supply from the SWR conductor rails at Dorking?

Secondly, in the Farnborough/ Frimley area, the route passes under the SWR main line from Waterloo and also the branch to Aldershot - all electrified. At Frimley the third rail is within yards! These give a wealth of possibilities. Would it be possible to take a DC supply from one of the nearby conductor rails?

This area is undulating and with three North Down stations. It would be down to the electrification engineers to decide the distances the conductor rails could be extended, and I suggest that this should be carried out using steel/aluminium composite rail to minimise voltage drop.

Connections to the existing third rail would call for DC switchgear, isolators and electrical fault relay installation. Introducing electrification on short stretches would also call for alterations to the signalling in the form of AC track circuits and impedance bonds or perhaps axle counters. Would it interfere unduly with the operation of trains along the affected donor route, or overload the transformer/ rectifiers at the supply sub-station?

These third rail installations would reduce wear and tear of the diesel engines fitted on the Class 769s, as well as cutting diesel consumption.

A decision to implement these works would depend upon experience in operating the bi-mode trains and the capital funds available. But the work does not have to be carried out all at once - a low-hanging fruit first policy could be adopted.

Perhaps the Flex trains could be used to extend the North Downs trains to develop an Oxford to Gatwick service - especially if and when the Didcot-Oxford line is electrified. R Eaton, Ashtead