One such advantage would be that a tunnel would still allow shipping to pass. A low bridge would need to be an opening or swing bridge to allow shipping to pass, which can cause traffic congestion. Conversely, a higher bridge that does allow shipping may be unsightly and opposed by the public. Bridges can also be closed due to harsh weather such as high winds. Another possible advantage is space: the downward ramp leading to a tunnel leaves a smaller footprint compared to the upward ramps required by most bridges.
Disadvantages
Compared with bridges
Tunnels require far higher costs of security and construction than bridges. This may mean that over short distances bridges may be preferred rather than tunnels (for exampleDartford Crossing). As stated earlier, bridges may not allow shipping to pass, so solutions such as the resund Bridge have been constructed.