Between July and December, seven projects are planned as part of replacing the south end of the viaduct, the elevated mile from South Holgate to South King streets. When complete, the southern mile of the viaduct will be replaced with a new side-by-side road that could connect to any future replacement of the viaduct's central waterfront section.

The seven projects starting this year are:

• Building a new city street, known as the East Frontage Road, between South Atlantic Street and South Royal Brougham Way. It will be used as a detour route when portions of Alaskan Way South are closed late in the project.
• Rebuilding Colorado Avenue South, and portions of South Atlantic Street and Alaskan Way South.
• Beginning the building of new bicycle paths.
• Beginning the relocation of railroad track along Alaskan Way South. Now beneath the viaduct, the track will be moved to the west.
• Improving the South Atlantic Street-Alaskan Way South intersection to improve traffic and freight mobility near Terminal 46.
• Beginning building of the new Highway 99 southbound lanes.
• Beginning building of the Highway 99 detour. A new, permanent southbound bridge will eventually connect to this temporary road, which will keep Highway 99 moving while the state builds a permanent connection between South Royal Brougham Way and South King Street. The Highway 99 detour will begin carrying traffic in late 2011.

One key part of the south-end replacement — two side-by-side, three-lane roadways — will be built between South Holgate and South King streets at a cost of $125 to $175 million. The state will open bids for that portion of the project April 14.

The south-end project is 40 percent of the overall replacement of the aging viaduct, damaged in the 2001 Nisqually earthquake.

The old south-end section, which is near the sports stadiums, will be torn down in 2012.

When the western half of two side-by-side, three-lane roadways opens, it will be used temporarily as a four-lane roadway while the existing viaduct is demolished. That's expected to be a six-month project, according to Ron Paananen, who heads the state Department of Transportation's viaduct-replacement project. Then, the eastern half of the side-by-side, three-lane roadway will be built.

"Our goal is to keep Highway 99 open as much as possible," said Paananen, who spoke Saturday while standing on the south end of the viaduct. The viaduct is closed this weekend for maintenance and testing.

In all, the south-end viaduct replacement project is expected to cost $483 million, which includes utility work, crossings over railroad tracks and property acquisition.

The state hopes to have the south end of the viaduct replacement completed in 2014.