The Norton Fitzwarren 1941 accident was in part signal positioning. Not stated in the accident report, but at Taunton station the starting signals for the Relief line were on the left, whereas on the Main alongside they were on the right, both being mounted on the platform. The accident train was at the platform on the Relief, and the bracket signal was pulled off for it to cross as normal to the Down Main on departure. The driver would have seen this while waiting. Shortly before departure the signalbox changed plans on learning of the approach of a nonstop on the Down Main, so reversed the points and pulled off for straight ahead on the Down Relief. It was normal for the fireman on the GWR on left hand platforms to look back on their side for the green lamp, look forward to the signal, and confirm "Right Away" to the driver. Driver has previously seen the signal off, but now it's a different one.
So many changes official and local followed in the days after the accident. If a signal reversion was done at the station, no starter was to be cleared for a different route until the loco whistled for it. Trains on the Down Relief were to be checked at intermediate Silk Mill box if the route at Norton Fitzwarren was not clear, as Norton was to send "Section Clear Junction Blocked" back to Silk Mill in such circumstances. Silk Mill starters were fitted with detonator placers to be used if the train appeared not to have slackened speed. And Taunton crews, at least, always both looked out on the left when ready to start.