Following is a summary of regulations governing the use of I-66 by all vehicles:

* Rush-Hour Restrictions: During weekday rush hours, only car pools and buses will be allowed on the new 10-mile section of I-66 between the Capital Beltway and the Theodore Roosevelt Bridge.

These restrictions will apply to eastbound traffic between 6:30 and 9 a.m. and to westbound traffic between 3:30 and 6:30 p.m. Commuters who violate these regulations face a penalty of $45 in fines and court costs, Virginia officials say.

A car pool or van pool is defined by Virginia authorities as consisting of at least four persons, including the driver. Such a vehicle is designated on I-66 signs as a "HOV/4," short for a High Occupancy Vehicle carrying a minimum of four passengers.

* Trucks: Heavy-duty trucks are prohibited from using the new section of I-66 at any time. The ban applies to trucks with two axles and six or more tires. The prohibition does not apply to Metro or other buses or to emergency vehicles.

* Traffic Signals: Starting next spring, entrance ramps leading to the new section of I-66 will be regulated by traffic signals. These are part of a computerized system designed to maintain an even flow of traffic on the highway. The ramp signals are not in operation now.

* Metro Bus Route Changes: Metro officials have announced changes in several express bus routes in Northern Virginia. Those changes are scheduled to go into effect with today's opening of the new I-66 section.

The changes, aimed at reducing travel time, affect bus routes 5A through H, plus 5Y and 5Z. Buses on these routes previously left I-66 at Fairfax Drive and traveled through Rosslyn to the District of Columbia. Now they will continue along I-66 and cross the Theodore Roosevelt Bridge to the District.

* Dulles Access Road: An exception to the car pool requirement will be granted for Dulles International Airport commuters beginning next fall when an extension of the Dulles Access Road is scheduled to open linking it with I-66. At that time, cars carrying fewer than four persons will be allowed to use the restricted section of I-66 during rush hours if they are heading to or from the airport.