From the videos that I've seen you would have to be pushing the authorised vehicle - any gap and you're snookered!
Reminds me when I nearly got trapped on the Lindisfarne (tidal) causeway.
I could see a van parked at the central refuge so reasoned that this was the 'warden' waiting to close the causeway. I drove until the water reached the engine and it started to misfire. I stopped and reversed (about a quarter mile) with the engine misfiring. Had to spend four hours in the pub (!) until the tide went down. As I drove back to the mainland the van was still parked at the refuge, having been submerged up to the headlamps (it was a Transit).
Map of Lindisfarne (you can pan and zoom it):-
http://wikimapia.org/#lat=55.6781652...14&l=0&m=a&v=2