Also FNRTTC went through the Rotherhithe tunnel which isn’t advisable.
I've done an FNRttC through the tunnel. Possibly even the same one as you. At FNRTTC time of night it's not at all busy, and so it's not dangerous. And there's a footway if you feel it necessary.
But it's still not advisable because it's
absolutely horrible and stinks.
My least favourite road is the A249 Sittingbourne road that runs NE across the Kent Downs from Maidstone to Sittingbourne and the Isle of Sheppey. It's a dual carriageway with very fast traffic and no hard shoulder to ride on. And the worst thing is, it's
in the way. There are almost no roads that cross it. It divides the Kent Downs in two. If it's in your way you have to join it, ride along it for a bit, then cross the carriageway to get off the other side . It's just plonked in the landscape and really awkward.
The A249 divides the village of Detling in two. A dual carriageway through the middle of a village, with no crossing. The inevitable result was a tragedy and there is now a footbridge called
Jade's Crossing, that was built only after campaigning by the bereaved parents of Jade Hobbs, who was killed along with her grandmother on the road.
Another road like this is the A127 Southend Arterial, which connects Basildon to the M25. It just forms a big E-W barrier across the landscape and if you're going north there are not that many crossing points. Roads that were formerly cross-roads are just blocked off. So you can follow a lane that meets the road, and if you wanted to continue the route on the other side you'd have to climb over the armco in the middle. Thank goodness for Google Streetview when planning routes.