What should A have done?

[LouBlue1507]

What should car A have done?

1. Brake, slow down and pull in behind car C

1. Continue to gather speed and continue in the same lane

Any other option?

Cotswold - I think its very dangerous to join the motorway and then slow down.

Either the lorry driver moved over to let people join from the slip road and he's wrong to then pull back in or he's been in the wrong lane for a while and so should have seen you joining

Like I said before I don't think you WU. Also I think I know the kind of road lay out you're trying to describe. Hard to know for sure without knowing the road markings though. Maybe find the road on google street view, and take a screen shot (minus road names)? If you can be bothered. I can only assume the lorry driver didn't see you, thought you were hanging back to allow them access or didn't realise how quick you were picking up speed?

Generally when two motorways merge the one joining has it's lane protected so traffic shouldn't move into it for a short while after the junction. If that was the case then you were right.

It doesn't sound as though either of you was driving brilliantly tbh.

The lorry would have been limited to 56mph and if the road was clear was presumably doing close to that speed? Your joining road speed limit was 60mph so you shouldn't originally have been going much faster than the lorry. The polite and safer thing to do would have been to join, let the lorry overtake you (which shouldn't have involved much if any braking), then change lanes behind it to speed up and overtake it.

The lorry driver clearly shouldn't have been moving into a lane with a car in it; I wonder if the driver didn't observe that there were two cars joining, saw car B behind and didn't twig that there was actually a car alongside as well.
So FWIW I think you were both at fault, the lorry driver more than you but that wouldn't have been terribly comforting if you'd been squished.

You are supposed to 'match your speed' to the traffic on the motorway - I just checked the regs of course I knew them anyway

Rule 259

Joining the motorway. When you join the motorway you will normally approach it from a road on the left (a slip road) or from an adjoining motorway. You should

give priority to traffic already on the motorway

check the traffic on the motorway and match your speed to fit safely into the traffic flow in the left-hand lane

not cross solid white lines that separate lanes or use the hard shoulder

stay on the slip road if it continues as an extra lane on the motorway

remain in the left-hand lane long enough to adjust to the speed of traffic before considering overtaking.

I see what you mean op, about it not being there already. So the motorway was either 2/3 lanes and then the slip road you're coming off then creates a 3rd/4th Lane on the motorway. Unfortunately though, I still think YABU. Although you did the right thing speeding up in the end otherwise it could have been an accident. But you undertook the lorry. And it's reasons like this that we are not allowed to undertake. Lorries have major blind spots. Lorry driver should have been more aware but you shouldn't undertake

You should have pulled on behind the lorry I think. Try to be more aware of what's on the road you are joining and moderate your speed better next time. Ideally you would never have been level with the lorry, and in his blind spot, you would have seen it as you rounded the curve of the slip road and moderated your speed to pull on behind it.

I'm confused as to how anyone thinks you were unreasonable. Can anyone explain?

I think YWNBU from what you said happened OP.

*Rule 259
Joining the motorway. When you join the motorway you will normally approach it from a road on the left (a slip road) or from an adjoining motorway. You should

give priority to traffic already on the motorway
check the traffic on the motorway and --match your speed to fit safely into the traffic flow in the left-hand lane
-not cross solid white lines that separate lanes or use the hard shoulder
-stay on the slip road if it continues as an extra lane on the motorway
-remain in the left-hand lane long enough to adjust to the speed of traffic before considering overtaking.*

Last point refers to this situation I think.

But she didn't overtake. she was still adjusting to the speed of traffic.

rightwhine the OP didn't match the speed unfortunately, she sped up - from her other post:-

I was car A and I sped up to get ahead of the lorry

The lorry driver probably saw that there was no-one in the merge lane when he was alongside it, they wouldn't be expecting someone to join behind them and then pull level on the inside!

I would have slow down. Even if the truck driver has good reflexes it take a while for a lorry to slow down stop. You were coming on the road and didn't have priority.

You should have slowed down. You attempted to undertake a vehicle with a massive blind spot. An accident would have been your fault. Unless of course you were rear ended by car B, in which case am accident would have been their fault for not maintaining a safe stopping distance.

Technically you shouldn't undertake but as you'd just joined slip road, the lorry clearly had seen that as he moved into middle lane. Therefore should've been more aware of where you were. I would've done same as you.