So for those who use the route a lot, was this the worst part of the journey, and how much difference would you expect it to make?
And in comparison, how much difference would a Worthing bypass make?
Not to mention those waiting to get out of Littlehampton (why wouldn't you) can have an equal wait South to North before Crossbush.Getting through / round Arundel can take a VERY long time, with the tailbacks at Crossbush heading West (can be 15 - 20 minutes, and sometimes worse), at the roundabout just past the railway station (all the way down the hill sometimes) and on the old bypass in the lead up to the roundabout over the bridge. The whole thing can easily add half an hour to the journey.
Coming the other way, we often get stuck coming down the hill past the White Swan just after switch from dual to single carriageway.
What happens generally is the locals go through Arundel to avoid the snarl ups and in turn snarl up both roundabouts as they try and rejoin. The same happens on the West bound at Crossbush as cars fly up the inside lane, as if to turn left to LA, but try and nip in later on, or even accelerate after the lights and nip in front of the cars turning right.
To your other question - we still need a bypass for Worthing, as the section up to each roundabout (Offington and Grove Lodge) snarls up under even moderate traffic, and Lions Farm also produces its own long tailback often to Grove Lodge. Chi can also add 30 mins onto a West bound journey, with most Sat Navs now directing people back through the City to avoid it.
That in turn puts pressure on the A259, but even then there's no way out as the coast traffic still gets hit at Chi or Worthing.
I always find West to East, through Arundel is quicker, but that's mainly because there's one set to traffic lights less.
By 2023 they'll probably be another 10,000+ homes built on the River Arun flood plains around Littlehampton (what could possibly go wrong) and another bypass will be needed.