Shirley Highway, long known In the Washington area as Interstate Rte. 95, is being changed to Interstate Rte. 395 because "routes should be so marked as to give maximum continuity between major control points."

That is what it says in the standards for highway numbers put out by a little-known but powerful group called the American Association of State Highway and Transportation Officials (ASHTO).

What it means is that the Capital Beltway, long known around here as Interstate Rte. 495. is being renumbered so that part of it will still be 1-495 and part of it will still be 1-495 and part of it will be 1-95. But if the Beltway is going to be Interstate 95, they have to call Shirley Highway something else. Hence, Interstate 395.

What is the rationale for all this?

"I'm glad you asked that," said Donald keith, the Virginia Highway Department's resident engineer. "We are doing this for the man who gets on in Florida and wants to drive to Maine and stay on Interstate 95 all the way."

What happens now. for those who have not tried it, is that someone coming north from Florida and following the Interstate 95 signs would cross the 14thehe Street Bridge into Washington, turn right on the Southwest Freeway. drive into the tunnel under the Mall west of the Capitol, and emerge, somewhat bemused, alongside construction barricades and red lights at the corner of New jersey Avenue and Massachysetts Avenue NW.

Then, the traveler can follow periodic signs that say "To 1-95" out New York Avenue and the Baltimore Washington Parkway until he getss back on 1-95. If e had read his map. he could have saved himself much grief and many traffic signals by taking the longer but easier Beltway around the city.

ASHTO decides what highway numbers will be. and believes that two-digit numbers should indicate through routes, but also that through routes should indeed be through. Since the District and maryland have both truncated their freeeway plans, there are no plans to build 1-95 through the District..

But now there will be an 1-95 around the Distrirct. Maryland has put up signs on the Beltway from its interresection with 1-95 around to the Woodrow Wilson Bridge saying both 1-95 and 1-495, and Vrginia is doing the same from the Wilson Bridge to Shirleey Highway. In about a year. the 1-495 designation will disappear on that section of the Beltway.

Meanwhile, 1-395 will appear. The Virginia Highway Deparrtment is erecting signs on Shirley Highway between the Beltway and the 14the Street Bridge; the D.C. Highway Department is doing the same thing on the bridge and along the Southwest Freeway to the tunnel under the Mail.

And then. if Virginia ever wins a lawsuit blocking construction of an expressway to National Airpoort. there will be an 1-595 over existing Rte. 1 to add the motorist's confusion. add to the motoristconfusion.