Transportation stocks, particularly railroads and courier companies, have been struggling in relative strength rankings lately, which may potentially be a sign of a slowing economy. Canadian Pacific (CP.TO), for example, fell out of the green zone of the SIA S&P/TSX 60 Index Report in March, spent the last two months sliding down through the yellow zone and yesterday, it dropped back into the Red Unfavored Zone after falling two spots to 32nd place.