Which junction is the one for Hassocks? Do you mean at Pyecombe?
The A23 was perfectly ice-free when I drove down it this morning at 7. In fact, it was so clear that it convinced me to drive over Falmer Road to Woodingdean, which I'd initially not planned to do. That was fine, too.
However...
I had a similar experience driving through Wivelsfield once. It had snowed hard while I was playing 5 a side at the Dolphin centre and I was heading home to Burgess Hill. As I approached the roundabout, the car in front decided to stop for no apparent reason. A single minute dab on my brakes...