Considering Birmingham, and we should as this is a Birmingham specific Forum, it should be remembered that pre 1948 the electricity supplied to the city's trams and trolleybuses was provided by the city's own manufactury and was probably at reasonable cost. Once nationalisation took place it had to be purchased from the new nationalised industry and was probably more expensive as it was no longer 'in house'. In 1949 the decision to abandon all electric traction in the city was made. Given that the city centre and some older suburban streets were narrow, at the time, this had also caused trams to loose favour due to their obstructiveness, to pedestrians and other road users. It had been planned to cease all tram operation in the city by 1944, but WW2 altered things somewhat delaying the final abandonment until 1953.
Trolley buses were initially seen, in the early 1930's by the transport department, as a good choice for tram replacement,* but they were not as flexible as the go almost anywhere diesel bus which at that time was gathering big support, besides as there were only just over 70 trolleybuses, among a diesel fleet of over 1500, they were something of an anachronism. Neighbouring cities such as Walsall and Wolverhampton kept trolleys for a few more years, the setting up of the PTE was the end for Walsall. The Lode Lane extension was authorised during WW2 as it was seen a more beneficial to operate electricity which was coal produced rather than use petrol or diesel buses when those fuels were in short supply and had to be brought in by sea.
* When the Dudley Road and Hockley tram routes were abandoned West Bromwich had hoped to use trolley buses as a replacement. This, they believed was better for them as their other neighbour, Walsall, also had them. However, Birmingham had other ideas and diesel buses took over.