SEATTLE -- Seattle Citizens Against the Tunnel (SCAT) will file an initiative petition with the city of Seattle Thursday that will force a public vote on the Alaskan Way Tunnel project.

SCAT said it will need 20,692 valid signatures in order to put the initiative on the ballot. Organizers have six months to collect enough signatures once the city approves the form of the initiative. The group said it is planning on halving that time in order to get the initiative on the ballot as soon as possible.

To gather signatures, SCAT will use unattended signing kiosks, all weather A-frame easels that will be set out in key 2007 tunnel/elevated vote neighborhoods, signing boards placed at select businesses, downloadable petitions that will be available through the SCAT web site, and personal signature gatherers.

Copies of the petition will be available Thursday at 10 a.m. at the City Clerk's office.

The final initiative petitions will be available for signing and signature gathering after the city clerk assigns a number to the initiative, approves the petition’s format, and provides a title for the initiative.

After approval, SCAT will announce when and where petitions will be available, the group said.