The Chota Motala interchange straddles the N3 freeway as a major access route to the Pietermaritzburg CBD in Natal, South Africa. It had been operating at above capacity for quite some time, evidenced by long delays in traffic on the Chota Motala Road (R33).
Of even more concern was the dangerous situation created by the backing up of traffic on the off-ramps from the freeway, resulting in through traffic on the N3 suddenly being confronted by stationary traffic in the slow lane. After evaluating several interchange upgrade options, authorities settled on a concrete bridge over the N3 which would create a much-needed third layer of traffic at this busy interchange.
The South African National Road Agency Limited (SANRAL) and the Mzunduzi Municipality appointed Aurecon, in joint venture with Illiso, for the detailed design of the upgraded interchange, with Aurecon responsible for all bridge work. Aurecon proposed the construction of an incrementally launched bridge seeing as the client’s main requirement was that any new bridge over the N3 had to be constructed without disrupting or endangering the heavy traffic on the N3 freeway. The incrementally launched construction method involves construction of the bridge superstructure section by section on one side of an obstacle and then launching them sequentially into their final position.
The bridge was designed as a 220 m long deck consisting of a single cell prestressed concrete box girder with a total of seven spans varying in length between 25.15 m and 36.05 m, arranged symmetrically around the centre. The deck is supported on 6 piers, of which four are founded on piled foundations and two are founded on spread foundations.
Over and above the interesting design, the bridge has also achieved exceptional aesthetics. The project team, with very close input from the South African National Road Agency Limited (SANRAL) and the Mzunduzi Municipality, took a decision that the webs and bottom slab of the bridge be more rounded that usual, and that aesthetic lighting as well as ‘golf tee’ shaped piers be made part of the bridge. The result is a bridge which is as elegant as it is structurally sound. Combined with the expected low maintenance cost during the lifetime of the bridge, Aurecon believes that our objective of providing the client with exceptional value for their investment has been achieved.