RHD - well that's the way we go to IKEA (as I say we rarely drive to Gatwick and when we do, we go via Bromley). Admittedly, I don't do the driving but I could swear we drive past Selhurst station on our rare jaunts down to Purley Way

The route I take is inbetween Selhurst Station and Thornton Heath rather than passing either where you can get held up in traffic

AMFM - got you. If you're going to ikea that makes sense. But if you're going to Gatwick you can avoid most of that traffic by cutting through Croydon via the underpass and joining the A23 much further down.