If i am driving up a slip road about to pull out onto a dc or motorway i indicate and check the mirror to see if its safe to filter out.During my motorcycling lessons i made a mistake of riding down the slip road and accelerating out in front of a lorry.Its the kind of thing that didnt cause the lorry to brake,i was (what seemed) quite a distance away,but the instructor freaked as he saw the risk i put myself in.The habit i have had for the past 15 odd years was to boot it and try to filter out safely.. and expect drivers to either pull out into the other lane or slow down/speed up to help me out.
If i was in their position,i would also do this for them.. but the fact is,if the traffic is heavy and theres no room to pull out,you may need to come to a complete stop.None of this slowing right down and thinking you are in the right by pulling out regardless.It was only after my bike test that i found this out.Only for the bike test i wouldnt have ever felt that i must treat a slip road as a junction and if need be, i must come to a complete stop.I was there and made these mistakes.You expect folk to help each other out but the fact is,if you are driving along and approach a slip road to your left,you do not have to slow down,speed up or move lanes.You may feel a bit of a dick for not making any effort to help the drivers filtering in but if it means a) having to slow down,putting yourself at risk from dozy drivers behind you. or b) pulling out into the faster lane because of someone elses lack of road knowledge and/or courtesy.. then you are just adding to a problem.
If the road is very quiet i still do pull out into the other lane to help drivers but not if its going to upset other drivers speeds and positions.I learnt my mistake on the bike training by an instructor that is no longer with us.This was the biggest bad habit i carried on since 1993 and only for him, i would still be doing it.
I now treat a slip road as a junction.Might sound daft but thats effectively what they are.Dont feel in the right when filtering out of them,you arent.