The internal width of the overbridges was only 9 f , but the railway 's passenger carriages were 5 f wide . This left less than 2 f clearance on either side , which was less than the minimum required clearance of 2 f. To alleviate this problem , McConnel proposed that the doors on one side of each carriage be permanently barred and the track slewed off-centre beneath the bridges . The internal width of the overbridges was only 9 f , but the railway 's passenger carriages were 5 f wide , leaving less than 2 f clearance on either side , less than the minimum required clearance of 2 f. To alleviate this problem , McConnel proposed that the doors on one side of each carriage be permanently barred and the track slewed off-centre beneath the bridges to allow adequate clearance at least on the side with doors , which would allow passengers to get out of the carriages if the train stopped underneath a bridge .