OSAKA -- Fifteen firms effectively control the repair and maintenance work for Hanshin Expressway Public Corp., even after public bidding was introduced in fiscal 2001 in a bid to end collusion, police sources said Wednesday.

The 15 companies include Kokuyo Construction Co., whose chairman, Masao Yamamoto, 62, was arrested Saturday on suspicion of rigging bids for projects sponsored by the Osaka-based public corporation, the sources said.

Hanshin Expressway Public Corp., funded by the central and local governments, operates a network of elevated toll roads in Osaka and its vicinity.