The Downtown Seattle Transit Tunnel (DSTT) will close temporarily to train and bus riders for about six hours Saturday morning, Aug. 9, while Sound Transit and King County Metro conduct operational tests for the planned 2016 opening of the University Link light rail expansion. The tests will run from 5 to 11 a.m.

Northbound Link light-rail service will stop at SODO Station south of the DSTT. To connect riders between Link and downtown locations, Link Shuttle Route 97 buses will operate between the DSTT stations and SODO Station. Bus routes that normally operate in the tunnel will use surface streets during the testing.

Heading toward SODO Station for connections with Link light rail, the Route 97 bus operates via Pine Street and Third Avenue and makes stops downtown on Pine Street just east of Fifth Avenue and at the island just east on Third Avenue, then southbound on Third at Union, Seneca and James streets.

During Saturday’s testing, trains and buses will simulate future rush-hour conditions in the DSTT. When the University Link extension opens in early 2016, trains will operate every six minutes; today, trains operate about every 7.5 minutes during peak hours.

The University Link’s 3.15-mile, underground light-rail extension to the University of Washington stations on Capitol Hill and at the UW is scheduled to open in the first quarter of 2016, six to nine months ahead of its original construction schedule and about $150 million under budget.

With the University Link addition, the light rail system is expected to carry an estimated 62,000 riders on weekdays by 2018.