Complex sentence: Bugis will be an interchange with the future Downtown Line and will serve as the northern terminus until 2015, when it would be replaced by Bukit Panjang as the second phase of the line opens.
Split into simpler sentences: Bugis will be an interchange with the future Downtown Line. It will serve as the northern terminus of the Downtown Line until 2015, when it would be replaced by Bukit Panjang as the second phase of the line opens.