TOLLS for three government tunnels are likely to be $1 cheaper from midnight tonight with legislators determined to reverse the Executive Council's decision to raise the charges from January 10. Legislative Councillor the Reverend Fung Chi-wood will lead the move to overturn the rise during today's Legislative Council meeting. The Governor-in-Council decided early last month to raise the toll for the Aberdeen and Shing Mun tunnels from $5 to $6 and the charge for the Junk Bay tunnel from $3 to $4. But standard procedure requires subsidiary legislation on the increases to be passed by the law-making body. The assembly has 28 days to decide whether to object. Mr Fung is expected to have the support of the 13 United Democrats legislators and the 17 members of the Co-operative Resources Centre in rejecting the new tolls. The Government, which will have to restore the charges to their original level from midnight if the revolt succeeds, was expecting the extra $1 to bring in $48 million in the next financial year. The main objection was that the rise would have bumped up the rate of return on investment on the three tunnels to 15 per cent. The return previously, when taken with the Lion Rock tunnel, was about 5.2 per cent. The Lion Rock tunnel was spared any increase because it had already achieved a good rate of return. Following the $1 rise, the return from the four tunnels could reach 10 per cent in the 1993-94 financial year, rising to 13 per cent in 1996-97. Officials are understood to be prepared to review the present arrangements, including whether the calculation of the rate of return should be a percentage of the total assets or a percentage of the turnover. Other government business activities, such as charges for aircraft using Kai Tak Airport, have already attained a 15 per cent rate of return. Sources said the Government was ready to review whether 15 per cent was the right ceiling. The review is expected to take several months. The sources said if the toll rise was withdrawn, taxpayers would be subsidising motorists. Funds for the tunnels would have to come from the Treasury, possibly diverting money that could be spent on other services.