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The Crown Prince Frederiks Bridge (Kronprins Frederiks Bro) is a bascule bridge that crosses Roskilde Fjord connecting Frederikssund with Hornsherred in Denmark.

History
Crown Prince Frederiks Bridge Crossing Roskilde Fjord at Frederikssund, where the fjord narrows considerably, dates back to the Middle Ages. By the 16th century, a ferry crossing had been established and by 1860s, traffic volume had increased substantially, as more than 30,000 people and 15,000 vehicles crossed yearly. By then, regular traffic jams were not unusual – close to 150 vehicles waiting for hours before being ferried over. The high amount of traffic was the result of increasing trade in Frederikssund. Further, Frederik VII, King of Denmark at the time, resided at Jægerspris Castle close by, which also added to the traffic volume.

In 1868, the ferry crossing was replaced by a wooden pontoon bridge, which was named Crown Prince Frederiks Bridge after Frederik VIII. The construction included 21 boat-like pontoons carrying the road-deck and a swing span to allow for ships to pass. Increased traffic meant this bridge had already out-grown its capacity by the end of the century.

It was not until 1935 the wooden bridge was finally replaced by the current-day Crown Prince Frederiks Bridge, this time named after Frederik IV.

Structure
The bridge is 151 m long and 9.1 m wide. It has three spans each 35 m in length and two bascule leaves of 15 m each. The clearance below the bascule span is 3.1 m. Spans are built with two longitudinal beams with a 8.4 m center-to-center distance except the bascule spans, which have a 8.5 m center-to-center distance.

The road-deck, originally 6 m wide and made from concrete, was replaced by a steel deck and widened to 7 m in 1983. The year before, a 1.5 m wide bicycle and pedestrian path was added on the outside of each side of the bridge.

The bascule spans originally had a wooden/steel road-deck – this was replaced with an all steel deck in 1967.

The bridge has three piers in total. Two of these, each 7.5 m long, serves as anchor points for the leafs. They also has machinery space and has the basement floor 2.65 m below surface. The third pier is located between the two spans on the western side of the bridge. All piers are made from concrete and seated on the seabed. The foundation is made-up of wooden piles 35-40 cm in diameter.

Future
By the early 1960s, traffic had increased to a level where this bridge too was becoming to small. Yet, it would be another 50 years before a new bridge would be decided – it finally happened on the 18 December 2014. The new bridge will not be a direct replacement as it will be built south of Frederikssund to reduce traffic through the city. Also, as the new bridge does not include a path for bicycles and pedestrians, the current bridge will still fill that role. The new bridge, which is expected to open in 2019, has been named Crown Princess Marys Bridge (Kronprinsesse Marys Bro).