Different traffic streams feeding into parallel lanes?

[samoht]

Above is J35 of the A14. The top left is the junction roundabout. The road at the bottom is the A1303 to Cambridge. The road at the right is the slip road off the A14 Westbound.
https://www.google.com/maps/@52.2137441,0.2166181,...

The Cambridge exit, after the roundabout has a ~200m section of dual carriageway with two lanes each way. Traffic leaving the roundabout at this exit is fed into the right-hand lane of this. Traffic leaving the A14 and wishing to turn left onto this road has a dedicated left-turn lane without give-way markings, which leads exclusively to the left-hand lane of the exit road.

View leaving the roundabout:


View approaching the roundabout along the sliproad:


There is a crest on both routes which makes the markings ahead harder to see, but isn't obvious from the GMaps camera car's elevated PoV.

View of the exit road just after the roundabout:



I frequent this junction, my issue is that a couple of times now, when I have been coming up the sliproad from the Westbound A14 and turning left at 50mph, I encounter slower traffic leaving the roundabout which at the exit, crosses over into the left hand lane without looking behind for approaching traffic and before the end of the hatched markings in the centre.


What's irritating is I'm pretty sure I understand how this junction is supposed to work - traffic from the different origins is fed into separate parallel lanes, and once established in said lanes and past the hatchings can use the regular mirror, signal manouevre process to make a safe lane change to the other lane if it's free. As such, if there's nothing ahead of me on the sliproad I feel I should be able to proceed unhindered through the junction, at least up to the end of the hatched markings (and thus end up ahead of rather than behind slower vehicles leaving the roundabout).

However since a certain fraction of drivers seem to think they should move into the left-hand lane as soon as they leave the roundabout and don't anticipate faster traffic in the left-hand lane, using the junction as intended seems unfortunately rather risky.

The other thing is, even if I in the left lane slow down to avoid 'undertaking' the traffic in the right hand lane, I can still easily then end up parallel to a vehicle in the right lane which may equally attempt to change lanes into me. If it's just one car leaving the roundabout that's more avoidable, but often it's one slow vehicle with one or two others following close behind. So even attempting to avoid 'risky' behaviour isn't straightforward.

I guess my questions are:
1) Does anyone else have an opinion on what should happen here if faster traffic is in the left lane passing slower traffic in the right at the roundabout exit? What would you do in this situation?
2) Has anyone else had experience of similar junctions, especially if it's ended up with any official determination of fault in a collision?

[Pica-Pica]

If I were entering and leaving at the first exit, I would be sure that I was in the right gear/mode to accelerate clear. You need to be sure that you are visible to the vehicle to your right (the one leaving from the roundabout).

I see no reason for the car coming off the roundabout to leave and enter the left lane early.

The road markings could be better, with double white lines, for a short stretch.

[nismo48]

Pica-Pica said:

If I were entering and leaving at the first exit, I would be sure that I was in the right gear/mode to accelerate clear. You need to be sure that you are visible to the vehicle to your right (the one leaving from the roundabout).

I see no reason for the car coming off the roundabout to leave and enter the left lane early.

The road markings could be better, with double white lines, for a short stretch.

+1

[sleepezy]

Pica-Pica said:

I see no reason for the car coming off the roundabout to leave and enter the left lane early.

It's the dawdlers getting out of my way as I come from the North side of that roundabout

But, being serious, I've used that roundabout multiple times a week for something like 20 years now from most directions in almost all traffic conditions and never had the scenario described. In rush hour traffic it's generally snarled up anyway and everyone uses both lanes - and most of the time in fast flowing traffic, vehicles not joining from the A14 West tend to move across well after the right hand bend onto the A1303 and much later than they could.