Limerick is the third largest city in Ireland, and the principal city of County Limerick and Ireland's Mid-West Region. It is the fifth most populous city on the island of Ireland. When taking the extra-municipal suburbs into account, Limerick is the third largest conurbation in the state, with an urban population of 90,757. Limerick is the second-largest city in the province of Munster, an area which constitutes the midwest and southwest of Ireland. The city is situated on several curves and islands of the River Shannon, which spreads into an estuary shortly after Limerick. Road infrastructure features four main crossing points near the city centre (an additional river tunnel to the west of the three bridges opened in July 2010). Limerick is one of the constituent cities of the Cork-Limerick-Galway corridor, which has a population of 1 million.