|From:||Pont Tal-y-bont (SH687415)|
|To:||Pont Felin Newydd (SJ133198)|
|Via:||Llan Ffestiniog, Bala, Llangynog|
|Length:||39.7 miles (63.9 km)|
|Meets:||A496, A470, B4407, A4212, A494, B4403, B4402, B4396, B4580, A490, B4393|
|Old route now:||A496, A470, A4212, A490|
|Route outline (key)|
The B4391 is a lengthy (albeit much reduced) 'B' class road across the south of Snowdonia and Mid Wales.
Originally the B4391 started on the A487 in Maentwrog. However, this first section was renumbered as part of an extension of the A486 in the late 1920s and so the B4391 now starts on this road at Pont Tal-y-bont. A remnant of the original numbering still exists as the A496 has to TOTSO here.
The road climbs steeply out of the valley of the Cynfal and crosses the moors to Llan Ffestiniog. Here it meets the A470 and multiplexes through the town. Again, the former numbering can be seen in the priority as the A470 has to TOTSO at this junction (in 1922 the B4391 was the only road here; a B-road (the B4408) appeared later but the B4391 has only been the junior partner in a multiplex since the 1940s, then with the A4108; the A470 arrived much later). The multiplex ends on the far side of the railway line and this time the B4391 has to turn off to regain its number.
The road climbs out of town and over the moorland again, eventually reaching a height of over 1200 feet. It then amazingly reaches the River Cynfal again and hugs the edge of the valley (with the river itself a vertiginous distance below) for over a mile, past the junction with the B4407. The road goes through woodland and finally reaches the watershed at over 1500 feet. It then descends fairly steeply into the next valley (that of the Tryweryn) where it reaches a T-junction on the A4212.
There now follows another multiplex which did not exist in 1922. Before the 1960s the B4391 followed the river downstream through Capel Celyn, eventually reaching the A494 in Bala. However, in the 1960s the river was dammed to form the Llyn Celyn reservoir (and drowning the village and the original route of the B4391). The new road along the valley and round the reservoir was deliberately built to Class I standard (and extended west to the now-A470 at Trawsfynydd); it was numbered A4212. The multiplex therefore takes the best part of 10 miles.
The A4212 ends on the A494 in Bala and the B4391 reappears on the opposite side of the staggered crossroads. It crosses the River Dee at Pont-y-Ceunant on the edge of the (natural) Bala Lake before meeting the B4403. The river valley is then followed downstream for a couple of miles (but this does not mean the road is flat). After meeting the B4402 the road climbs out of the valley via some hairpin bends before crossing the moors once again. The road reaches a summit of well over 1500 feet on the Berwyn Range before descending an infant river valley appearing on the right. This becomes the River Eirth, which flows into the Tanat near the twin villages of Llangynog and Pentre.
The B4391 follows the Tanat Valley downstream from Pentre to Penybontfawr, where it meets the B4396. There is a short multiplex out of the village before the B4396 continues along the valley and the B4391 climbs into the hills again. This is not moorland now but farmland. Eventually the road descends into the next valley. It crosses the two main tributaries of the River Cain before meeting the B4393 to the west of Llanfyllin. This is the end of the B4391: the road ahead is the A490, making this junction a point where three separate roads all end. Originally the B4391 continued further to end on the A491 (now A458) in Welshpool; all this became the A490 in 1935.