|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 which runs across the south of the Snowdonia National Park and into Mid Wales.
Originally the route started on the A487 in Maentwrog. However, the first mile and a half from there to Pont Tal-y-bont was renumbered in the late 1920s as part of an extension towards Blaenau Ffestiniog of the A496. A reminder of how the routes were first laid out is the TOTSO performed by the northbound A496 at the fork which marks the B4391's current western starting-point.
Our road climbs quite steeply onto the ridge separating the valleys of the Teigl (left) and Cynfal (right), a sharp right-hand bend followed by a series left-hand curves eventually bringing us into the old slate-quarrying village of Llan Ffestiniog. Here, at the junction of Ffordd Blaenau and Pen-y-bryn, we meet the A470, which for a quarter of a mile takes over our route until, at the far end of the village, immediately after passing under the mothballed Festiniog and Blaenau Railway line, we turn left and the B4391 continues its eastward run.
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.