Virginia officials yesterday approved rush-hour car pool restrictions for the inside lane of the Dulles Toll Road beginning next fall and cleared the way for possible use of the shoulder as a fourth traffic lane during peak periods.

The resolution approved unanimously by the Commonwealth Transportation Board in Richmond stops short of establishing four permanent lanes in each direction, as some officials had urged. But it apparently resolves safety concerns raised by others.

Inclusion of the toll road in the region's growing network of car pool lanes will require the approval of the Metropolitan Washington Airports Authority, which owns the right of way for the toll road and the parallel Dulles Airport Access Road.

The authority's staff has termed the plan "workable."

Currently, part of the Interstate 95 shoulder in Northern Virginia converts to a traffic lane during peak hours.

The toll road car pool lanes would be marked with diamonds but would not be separated by barriers.

Vehicles carrying three or more people -- plus buses, emergency vehicles and airport traffic -- would be permitted in the restricted lane eastbound from 6:30 a.m. to 9 a.m. and westbound from 4 p.m. to 6:30 p.m. on weekdays. Violators would be subject to fines.

A year ago, the state began widening the 15-mile toll road from two lanes to three in each direction, with work scheduled to be completed by fall 1991.

Some officials wanted to designate the inside lane as a "high-occupancy vehicle," or HOV, lane once the widening was completed.

However, the airports authority said it could be dangerous for motorists on the limited-use access road trying to merge onto the toll road car pool lane, and the issue was left unresolved.

On Monday, the Rail, Transit and HOV subcommittee of the state's policy-making Commonwealth Transportation Board discussed building a new "flyover" ramp that could carry access road traffic over the busier toll road and funnel it onto Route 7 in Tysons Corner. At the same meeting, some officials noted that while the toll road is being widened, the shoulders are being made wide and strong enough for conversion to a fourth traffic lane in each direction if the need for them arises.

"We won't have to go back to square one" to expand the road to four lanes, said transportation board member Mark Warner.

Yesterday's transportation board resolution approves the car pool restrictions and calls for completion of the special Route 7 ramp no later than six months after the widening is completed.

Officials said the ramp and other adjustments will add an estimated $3 million to the $45 million cost of the toll road widening.