One such advantage would be that a tunnel system would still allow shipping to pass. A low bridge system would need an opening or swing bridge to allow shipping to pass, which can cause traffic congestion. As with bridges, albeit with more chance, ferry links will also be closed during adverse weather. Strong winds or the tidal limits may also affect the workings of a ferry crossing. Travelling through a tunnel is significantly quicker than travelling using a ferry link. (Wikipedia)
Contents:
The R file would be found here and the LCI materials used in the whole system is here.