I've copied this over from another thread as it may be seen by more people here.
The following are links to a fairly comprehensive guide on placement of OHLE. Hope it's of use to some of you.
Part one - http://www.rmweb.co.uk/community/index. ... ain-track/
Part two - http://www.rmweb.co.uk/community/index. ... ved-track/
Part three - http://www.rmweb.co.uk/community/index. ... or-points/
Part four - http://www.rmweb.co.uk/community/index. ... r-overlap/