LEGISLATORS are concerned about a proposal to allow the operators of the planned Western Harbour Crossing great flexibility in setting tolls. They say it favours the operator at the expense of tunnel users. Under the proposed scheme - which is subject to the scrutiny of the Legislative Council - the Government and the sole bidder for the crossing would decide on a guaranteed rate of return on capital. During the period the operator was repaying debts, it would be allowed to increase tolls until the rate of return met the guaranteed level. After that, the operator would have to pay royalties if its rate of return was higher than that guaranteed. United Democrats legislator Mr Albert Chan Wai-yip said he found the proposal unacceptable, because the operator could bypass Legco when increasing tolls. According to United Democrats estimates, the Western Harbour Crossing could be charging a $30 toll when it opened in 1997. The toll for the Cross Harbour Tunnel is $10. The price differences between the two tunnels might force the Cross Harbour Tunnel to increase its toll, Mr Chan said. As the Wharf group would be running both tunnels, he suggested the Cross Harbour Tunnel subsidise the new crossing. The Government should drop its $5 surcharge on the Cross Harbour Tunnel toll and allow the operator to get the full $10 toll, he said. Mr Zachary Wong Wai-yin of Meeting Point said: ''It sounds as if the operator is allowed to increase the toll entirely at its own discretion. The scheme is designed to protect the operator rather than tunnel users.'' Mr Leung Kwong-cheong of the Association for Democracy and People's Livelihood said the association might reject the scheme because it was too favourable to the franchisee. He called on the Government to find more bidders for the tunnel. Mr Edward Ho Sing-tin, of the Liberal Party preparatory committee, wondered why the Government had proposed a scheme using the rate of return on capital to decide the toll. The method was dropped by bus companies after severe criticism. Legislator Mr Samuel Wong Ping-wai said the scheme was reasonable because there was only one bidder for the project.