Third Avenue through downtown Seattle will be restricted to buses and cyclists for more than 12 hours beginning in September.

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Between Stewart Street to just south of Yesler Way, drivers will no longer be allowed to travel along the busy street from 6 a.m. to 7 p.m. for more than one block. Permitted commercial vehicles will be allowed to use the street from 9 a.m. to 3 p.m.

The reason, according to the city, is to keep pace with the demand for bus service to and through downtown.

“There’s a huge amount of demand,” city traffic engineer Dongho Chang said. “And even some of our popular routes are so full, people are being left because they can’t get on the bus.”

On a normal weekday, more than 2,000 bus trips are made on Third Avenue, according to the city. Approximately 100,000 people are picked up and dropped off along Third.

The restrictions for drivers will be seven days a week.

An exception will be made for people driving one block. Those drivers must turn immediately, according to Chang.

Additionally, drivers will no longer be able to make left turns off Third Avenue.

By March 2019, every bus stop on Third Avenue between Yesler Way and Denny Way will receive an ORCA card reader and real-time bus arrival sign in order to speed up bus service.

The change comes as the city implements recommendations of the One Center City action plan. The city is gearing up for what is being called the “period of maximum constraint,” a time when the major construction projects combined with a growing population will create some of the worst gridlock we’ve seen in the city.

According to the plan, the change to Third Avenue was originally recommended to be made by the first quarter of 2019. The three justifications were:

Improves auto compliance by simplifying operations of 3rd Avenue.

Improves pedestrian and bicycle safety by reducing the number of vehicles turning from 3rd Avenue.

Maintains access for freight and passenger loading.

Additional recommendations from the action plan show more transit-focused may be on the way.