You can rent a car in Belize City and see most of the highlights of the Hummingbird Highway on a day trip. It's about an hour to Belmopan where the Hummingbird starts, and maybe an hour and a half from there to Dangriga if you don't stop along the way.
You could also take a bus but you wouldn't be able to easily get on and off to see the sights.
There are no water taxis to San Pedro from Dangriga.
--Lan Sluder