Returning from Ireland to Worcester last night I took the A465 Heads of the 
Valleys Road - a route which I don't know well. The descent from the 
summit - just west of Brynmawr - of 1350 ft down the gorge to the Usk Valley 
at Gilwern is quite sudden, and when I got home I was prompted to look at my 
atlas to see which route the railway had taken. Given the topography, it 
must have been very similar - in which case the section from the valley 
floor at Gilwern up to Brynmawr must have been prodigiously graded - the 
road is billed as 5%. Even allowing for the railway to gain some height 
between Abergavenny and Gilwern, there must have been miles of 1-in-40-ish 
grade. Is that correct?

Regards

Jonathan

On 21 Sep, 00:44, "Jonathan Morton"
 wrote:
> Returning from Ireland to Worcester last night I took the A465 Heads of the
> Valleys Road - a route which I don't know well. The descent from the
> summit - just west of Brynmawr - of 1350 ft down the gorge to the Usk Valley
> at Gilwern is quite sudden, and when I got home I was prompted to look at my
> atlas to see which route the railway had taken. Given the topography, it
> must have been very similar - in which case the section from the valley
> floor at Gilwern up to Brynmawr must have been prodigiously graded - the
> road is billed as 5%. Even allowing for the railway to gain some height
> between Abergavenny and Gilwern, there must have been miles of 1-in-40-ish
> grade. Is that correct?
>
> Regards
>
> Jonathan

Yes, in fact some parts are 1-in-35ish!