Opponents of Honolulu's planned $3.7-billion commuter rail system today announced they've gathered 20,000 signatures in an attempt to put an anti-rail initiative on the November ballot.

That's about half the group's goal of gathering 40,000 signatures by Aug. 1. Stop Rail Now contends the public has a right to vote on whether the city should proceed with the transit project, which would be the largest public works project in state history. The petition drive started April 21.

The City Clerk's office maintains the group will need the signatures of at least 44,525 registered voters.

Rail proponents, including Mayor Mufi Hannemann and pro-rail council members, say a vote is not needed as the public has input on the project via elected representatives and public hearings.

Hannemann hopes to start construction on the 20-mile commuter rail late next year. The system, which would connect West Kapolei with Ala Moana, is scheduled to open in phases between 2012 and 2018.