Knocked down railings are a regular feature of our bridge.... these have been hit in just the last week - and there are several others.
If you're short on time, here's a Coles Notes version:
1. make sure your vehicle is within the posted 2 tonne limit
2. make sure your vehicle fits between the curbs and railings
3. drive straight (look in the distance, not at the end of your vehicle's nose)
4. drive slowly
5. though they can be difficult to see, vehicles exiting The Island have priority (makes sense if you think "Emergency", right?)
Pretty simple. Otherwise, you'll either take out the railings or even end up scraping along like this, which is probably a stressful way to start your holiday. Oh, and it's worth mentioning there's no boat launch on The Island (incidentally, speedboats are prohibited between the railway bridge on Morrison Road and the river mouth).