Your preferred candidate is incorrect. It is required to support increased train traffic... period. Diesel has nothing to do with the requirement. If they electrify it is still required for electric trains. The purpose of the track is so that trains going in opposite directions on the Barrie line can be more freely scheduled without delays while waiting for opposing trains to pass and electricity doesn't change that. Secondly, it doesn't make it any more difficult to expand the West Toronto Railpath because (a) there is already no bridge available over Queen, and (b) there is still room on the north side of the corridor to put the Railpath, if there was a budget, even with the additional track. If there would be no infrastructure for the Railpath with or without the additional track and there would be enough space in the corridor with or without the track then the argument makes no sense.