AN internal government transport study has recommended motorists be charged the same toll for the Western Harbour Crossing and the Cross-Harbour Tunnel by 1997. If the recommendation is accepted, motorists can expect to pay $30 at 1997 prices - $20 at today's prices - for each tunnel. The study also calls for the toll for the Eastern Harbour Crossing to be half that of the Western and Hunghom links. The proposals are contained in the updated second Comprehensive Transport Study and are expected to prompt concern from legislators. The present charge for cars using the Hunghom tunnel and Eastern Harbour Crossing is $10. Legislators, critical of arrangements for the Western Harbour Crossing, have already questioned whether the proposed $30 toll would lead to higher tolls at existing tunnels. However, officials, aware of the sensitivity of imposing higher charges, say the study's recommendations are for transport modelling purposes and do not necessarily reflect what will happen. Legislators will be fully briefed on the study at Thursday's Transport Panel meeting. Independent legislator Samuel Wong Ping-wai yesterday expressed concern at the recommendations and said the Government needed to explain whether it would impose the same toll for the Western and Hunghom links. Officials see two main effects of different tolls between tunnels: persuading drivers to switch from one tunnel to another, and encouraging them to use public transport. The Post disclosed yesterday that motorists face a sharp increase in registration tax, as part of a government drive to curb the number of cars on the road. The Government is understood to be alarmed at the increase, which hit 11 per cent last year - more than twice the ''acceptable'' level of five per cent. According to government projections, the Hunghom tunnel will be the busiest in 1997. Assuming different tolls at the two tunnels - the Western link charging $30 and the Hunghom tunnel $10 - the Western Harbour Crossing would attract 75,000 vehicle trips a day, compared with 120,000 for Hunghom. The Eastern Harbour Crossing is forecast to handle 85,000 vehicle trips a day. The projections are contained in a government document submitted yesterday to members of the Legco committee studying the Western Harbour Crossing Bill. The Government predicts the daily vehicle flow of the Western Harbour Crossing will rise to 100,000 in 2001 and reach a peak of 120,000 by 2006. This compares with 120,000 in both 2006 and 2011 for the Hunghom link.