I haven't seen any suggestion that the bridge with the clearance problems is weak.
The road over Trinity Street bridge was dualled in the late 60s or early 70s so the bridge may have been reconstructed then.
Similarly Windsor Bridge at Salford Crescent, which has also been named in this thread as a candidate, may have undergone reconstruction either when the Windsor Link was built, or during one of the stages of dualling the A6 through Salford. One of those stages included building the road bridges over University Road and the slip road to Albion Way.
Not sure about Crescent as I don't alight there often, but when I last got off at Bolton the other day I stood under the bridge whilst the train went onwards (Clitheroe service) and it seemed to me that there wasn't much clearance with an imaginary pantograph to where I was standing - easily enough for me, but I'm a short arse, but a say 6'9" bloke with a big brolly might conceivably be within striking distance of the potential OLE and I presume NR would need to consider this type of extreme to cover themselves. I'll take some photos next time I'm there to illustrate..
IIRC Trinity street was rebuilt in the 80's when they demolished the original station - some great pics of the old building and its demolition here -
http://www.rmweb.co.uk/community/index.php?/gallery/album/1273-bolton-trinity-street-station-1980s/ - again I think due to corrosion issues - a shame, as the original building was much nicer than what we have now (which you could argue is really mainly on Newport Street rather tha Trinity St, but I digress), but at least they have left the platform buildings, even though these seem to be largely unused...

The concrete plinth is still there between platform 3 & 4 that carried the supports for the building, which you can see in the photos.
Bolton is very busy at commuter times, hopefully once the new bus station opens it will increase.. We shall see....
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Well good grief I hope the current Joseph Locke lives a lot longer than the mere 55 years of the previous one !
Indeed.
Reading up on Mr Locke Esq. (Victorian version) it would seem that we have more to thank him for than the Stephensons..(not underestimating G&R S contributions to railway) but...
Locke's greatest legacy is the modern day West Coast Main Line (WCML), which was formed by the joining of the Caledonian, Lancaster & Carlisle, Grand Junction railways to Robert Stephenson's London & Birmingham Railway. As a result, around three-quarters of the WCML's route was planned and engineered by Locke.
https://en.wikipedia.org/wiki/Joseph_Locke#Later_life_and_legacy