It's finished. After 3 1/2 years of construction, legal battles, hazardous driving conditions and more than 3,600 accidents, the 22 miles of the Capital Beltway in Virginia have been widened from four and six lanes to eight.

For many commuters, completion of the $87 million project is a dream come true.

"It's super!" said D. J. Medders, adding that he "dreaded every day" while the road was under construction.

"The road got on my nerves," said Medders, as he described bottlenecks that held him up for as long as one hour and 45 minutes and wooden construction barricades that "were so dangerous they made everyone nervous."

"I saw 10 or 12 accidents every morning - some just fender-benders - in the construction area. People would concentrate on not getting too close and then they'd hit them anyway - and when it was raining, forget it," said Medders.

Now that the road is complete he said he has noticed fewer accidents and he gets home 15 to 20 minutes earlier.

Dennis Gribok, assistant Virginia Highway Department resident engineer, said 85,000 to 90,000 cars a day are now traveling the Virginia section of the Beltway - a traffic flow exceeded in the Washington area only by the 100,000 cars traveling Shirley Highway.

Girbok said the final portion of the Beltway - from Route 50 north to the American Legion Bridge at Cabin John - was completed July 7 and that all that remains to be done is a "half day's work" installing photocells to automatically turn on road sign lights at dusk.

He said the widening was finished about a year later than expected, primarily because concrete and earthen noise barriers had to be constructed along segments of the road when homeowners complained that noise levels exceeded federal standards.

The highway department said the barriers also were one reason why construction costs exceeded projected figures by about $9 million. The widening was financed through a sharing agreement, with 90 per cent federal funds and 10 per cent state funds.

As construction along the 22-mile highway segment neared completion, the highway department noted continued declines in the number of traffic accidents reported.

The largest number of accidents, 1,355 was reported in 1975 and that figures dropped to 1,191 in 1976. In 1974, 1,102 accidents were reported.

There were 406 more reported accidents in 1975 (in the middle of the highway widening) than in 1973, prior to road construction. The Virginia Highway Department estimates 3,648 accidents occurred on the Virginia stretch of 1,495 from 1974 to 1976.

Sally Free of the Center for Auto Safety (an independent consumer agency financed primarily by State Farm Companies, Foundation of State Farm Insurance) said one of the reasons for the large increase in the number of accidents and injuries on 1,495 was that "22 miles is too long for a construction zone."

Free said the highway department couldn't realistically expect motorists to travel at the posted 45 m.p.h. construction speed for that great a distance. She said a number of studies show motorists tend unconsciously to accelerate over long distances.

Highway Department officials blamed accident increases on motorists who refused to obey the speed limit. At the peak of the accidents, Fairfax police said they were averaging 68 tickets per day to speeding motorists.

Construction workers also complained about speeding cars, and a 1974 memo from a construction engineer claimed at least three accidents occurred in the construction areas daily.

Four construction workers were killed by speeding vehicles that crashed through barriers or disregarded construction markings. One worker was decapitated when he was struck by a wooden panel jutting from the back of a pickup truck.

In 1976, 10 people were killed along the construction area in fiery crashes and freak accidents - many involving protective wooden barricades, which when hit were found to knock cars out of control and which often splintered driving wooden spears into automobiles.The large number of accidents caused by the barricades resulted in the construction area being dubbed "Toothpick Alley."

The accidents led to a suit coordinated by the Auto Safety Center, which officials said led to an out-of-court agreement to ban such barricades on Federal highway construction sites with operating speeds of more than 20 m.p.h. It also resulted in a safety officer being appointed to insure detours, road markings and the road itself met safety standards while construction was under way.

Gribok said the highway department still kept some barricades up after that agreement, but that the department took care to see they were properly aligned to avoid accidents.

Now the Beltway widening is complete, the construction hazards are gone and traffic is moving freely.

But Ron E. Duell, assistant regional manager of Boise Cascade, and a frequent Beltway user, isn't as optimistic as many commuters. For him, highway construction seems a bit like a never-ending nightmare.

He prophesies that now that the road is complete it will "be ready for major repairs in six months."

Duell views highways as many people think of cities - as something in a state of flux, being constantly outgrown or outdated.

His opinion finds some basis in the early history of the Virginia portion of the Beltway - when the road was found to be too small to handle traffic flow after only one year.

Gribok, however, said the highway department is more optimistic. He said he expects the newly widened road segment adequately to handle traffic till at least 1995 without any major problems.