Seems to me that the only long-term solution is to build a raised concrete causeway from the bridge past RV to where the land starts to rise. Built on solid foundations (pilings) it should withstand anything mother Nature is likely to throw at it, as well as being immune even to heavy traffic. This could have been built at the start of RV development and should have been imposed as a pre-condition. Given that it wasn't (?) I don't know now who'd pay for it - it wouldn't be cheap. In the long term though it would be the best value, as well as being far more pleasant for the people of RV to look out on and use.
Of course, instead of the expense and disruption of making up the existing road all the way to the border to motorcoach standards, we could take the Seattle approach of building a concrete highway on stilts all the way down the seafront. Built properly it'd be immune even to violent storms, and concrete bunkers could be added at intervals to provide hurricane shelters.
AmbergrisCaye.com 
