Bridge numbering on the WHR
Based on an email from Andy Savage -WHR E-group posting 26482
Some years ago discussions were held about how to number structures along the WHR. There are Bridge numbers for construction purposes - construction is now (January 2008) at 200 - and level crossing numbers currently reaching to around 110 (140 and 75 in Nov 2006.). In construction terms the railway is at 19.5 km. But all of these sequences are based on a zero point at Dinas North, and do not allow for the section from Caernarfon, as it was built separately as a Light Railway rather than under the Transport and Works Act. It was thus very difficult to work out where you were if something went wrong unless you know every bridge and level crossing by number or name. That is just about practical on the FR, with 40 odd level crossings in 12 and a bit miles, but was not going to work on the WHR.
Andy Savage, in the course of his professional life, has mainly worked on the London Midland and Western Regions. The LMR numbers bridges from 1 to whatever, as our with construction sequence. If a random extra bridge has to be put in between say bridges 156 and 157 it becomes 156A - and so on up to 156G if you're putting in extra culverts in Beddgelert Forest LMS style! On the GWR the location of bridges is done by the mileage and chainage - thus a bridge at 19m35c is bridge 19.35. Any extra bridges just fit in the sequence, and it's quite rare to have more than one bridge within a chain (66 ft) distance.
Andy argued strongly for the GWR system for the WHR, and as he was Ops Director at the time he got his way. The WHR is a metric railway, and starts at Caernarfon, so everything measures in kilometres from there. However to avoid confusion with the FR proper, which goes from 0.00 to 12.47 (in imperial miles and chains), they started at 20km, at Caernarfon footbridge. This is thus bridge 20.00. Accordingly the bridge number 50.01 means that this bridge should be 30.01 km from the Caernarfon footbridge. I presume that someone calculated this out - although as we have a 50m difference between construction mileage and reality in Beddgelert Forest it might be not quite accurate.
All of Phases 1 to 3 are numbered this way, and a full set of km and half km posts were positioned, starting early in 2007. Andy presumes that similar posts and bridge / crossing plates will go up on Phase 4 when it's finished. UB182, The Nantmor road bridge, was the first to be so marked as UB50.01.
One other point - Caernarfon "zero point" is nominally set at the first footbridge and is actually marked as being at 20km. This was done to ensure no confusion with the Festiniog, which apart from using imperial measurements, only extends approximately 13.6 miles.
1 = Bridge 1 on the railway - probably numbered back in 1997
WHR 20 = notional kilometre distance marker - starting at 20 removes similarity with FR numbers
OB 20.00 = using a standard system for locating structures on the line