...................culverts have a concrete (sometimes or materials can be used too) floor allowing water to flow smoothly through it.

box culverts are usually made up of reinforced concrete (rcc). some box culverts can be built using composite structures and are great when water needs to change direction or when a large flow of water is expected. box culverts can also be installed in such way that the top of the culvert is also the roadway surface. the most challenging part of installing these type of culverts is that you generally will need to have a dry surface to install the culvert, so dewatering or diversion of the water will be needed to complete the installation.