The 5-kilometre MCE connects with the southern end of the KPE and its junction with the ECP to the eastern end of AYE. This links the eastern and western parts of Singapore to the New Downtown, currently being developed in the Marina Bay area. The MCE, with five lanes in each direction, handles the large number of commuters to be drawn to the offices, homes and recreational attractions there. It opens access to the Marina Bay Cruise Centre Singapore in Marina South and the existing Marina South Pier. Bus services 30, 30e, 522, 523, 538, 539, 545, 553, 566, 569, 584, 621, 661, 672, 736, 763, 767, 783 and Tanjong Rhu to Raffles Place/Suntec City Premium Service are the only buses to use the expressway following amendments to its route.
Plans to extend the KPE to join the AYE began on 9 March 2006 to relieve congestion of the East Coast Parkway, and would be called Marina Coastal Expressway. Feasibility studies were conducted for the new expressway, and then Transport Minister Raymond Lim later announced on 27 July 2007 that approval had been given for the construction of a new 5 km long Marina Coastal Expressway at a cost of $2.5 billion. The expressway, which includes Singapore's first undersea tunnel, links the East Coast Parkway and Kallang-Paya Lebar Expressway to Marina South and Ayer Rajah Expressway and opened to traffic 29 December 2013. The expressway comprises a tunnel, while the rest are at grade or depressed, with a view of the Singapore Strait. The tunnel includes a stretch that travels under the seabed, away from the Marina Barrage. This had posed particular engineering challenges in the tunnel construction as large amounts of water were let out from the barrage from time to time. At its deepest point, the expressway lies about under the seabed. The long MCE is Singapore's most expensive expressway. On 28 April 2009, the Land Transport Authority revealed that it has awarded about S$4.1 billion worth of contracts, much more than the initial estimate of $2.5 billion. The construction of the MCE also required undersea dredging. More than of land was reclaimed to build the MCE. In contrast, the KPE, which is and has portions running under canals and rivers, cost only $1.74 billion. After the MCE was opened, the segment of the ECP between Central Boulevard and Benjamin Sheares Bridge was downgraded to become Sheares Avenue. The segment of the ECP between the AYE and Central Boulevard was permanently demolished. The first few days of operations was plagued by heavy traffic congestion due to drivers' unfamiliarity with the expressway as well as connections with other roads and expressways. There was reportedly heavier than usual traffic, compared to using the old route via ECP, on 29 December 2013, the first day the MCE opened. The situation was exacerbated on the next day with the Monday morning peak hour traffic. However, the majority of drivers are aware of the road changes. Since June 2014, the Marina Coastal Expressway became the anchor road from the west to the east. On 28 September that year, with the road changes in Marina South area, the Prince Edward Road exit was removed and was replaced by Straits Boulevard exit with the ERP gantry being relocated from Prince Edward Road to Straits Boulevard.
