At 12 feet long, the busy Straits Pond bridge in Hull is shorter than many of the popular minivans and other suburban family vehicles that zip across it. Technically not a bridge but a culvert little noticed by motorists, the Route 228 span, which connects Hull to Hingham and Cohasset, has deteriorated and needs to be replaced.

But the seemingly straightforward job has proved to be anything but simple -- or inexpensive.

The cost of rebuilding the span? About $1.4 million, or more than $100,000 per foot.

The time needed? Eight years at last estimate, from the first report of problems to the end of construction in 2008 -- although that date is still tentative. Work has involved the federal and state governments, as well as the three towns.

''It's getting Big Dig attention," said Hull Town Manager Christopher McCabe.

The bridge is emblematic of why it costs so much and takes so long to repair bridges across the state. What would appear to the layman to be a relatively uncomplicated matter -- putting a steel and concrete structure across a stretch of water or roadway -- can be complicated, time-consuming, and very expensive.

While the work on the Straits Pond bridge is exceptional in both expense and time, other spans in the area have also faced expensive and drawn-out repairs or replacements. Among these are the Fore River bridge between Quincy and Weymouth, the Bullard Street bridge in Walpole , and the South Street bridge in West Bridgewater.

Officials and engineers note that each bridge involves unique, time-consuming engineering and construction demands, such as working over and in water. Obtaining federal, state, and local permits can take months.

Environmental considerations, such as spawning fish, must be taken into account. Utility lines -- for electricity, gas, telephone, or water -- may have to be relocated. Meanwhile, anxious neighbors are concerned about detours.

The state spent $206 million on bridge repairs last year, up from $146 million in 2003, yet it is struggling to keep up.

For almost every bridge that is repaired or replaced, another is added to the state's to-do list, an indication of the toll taken by rugged New England winters, corrosive road salt, and heavy traffic.

The state listed some 550 bridges with structural problems in January 2003; it hopes to whittle that to 440 by 2010. About one in eight of the approximately 4,400 state- and town-owned bridges in Massachusetts is listed on a year-old federal database as being structurally deficient. (An additional 600 bridges, either privately owned or belonging to state agencies, have similar problems, but are not maintained by the state.)

State- and town-owned bridges with serious problems are shut down or have load restrictions placed on them. Because of the expense and how such projects are funded, the state often handles major repairs or the rebuilding of municipal bridges that are at least 20 feet long, with the federal government generally footing 80 percent of the bill.

South of Boston, roughly 10 percent of some 600 bridges are considered structurally deficient.

The situation is not likely to improve soon -- in this area or across Massachusetts. Nearly 40 percent of bridges in the state were built in the 1950s and 1960s, when Americans took to the highways in droves, and those bridges are now reaching the age when many will soon need extensive repairs and renovations.

Among the local bridges needing expensive repairs or replacement:

The state has spent $50 million to build a ''temporary" span over the Fore River between Quincy and Weymouth. The temporary bridge, which opened in 2003, is designed to last 15 years. The original was dismantled in 2004 because of its terminal condition.

A new, permanent bridge will cost an estimated $80 million and might be completed by 2012, said Alexander Bardow, director of bridges for the state Highway Department. The first contracts for preliminary design work will be advertised this summer, he said.

The permanent bridge will be movable, said Bardow, meaning it will be either a vertical-lift bridge similar in design to the temporary bridge, or a drawbridge similar to the original.

An ownership issue has snarled efforts to repair the Bullard Street bridge in Walpole. The municipal bridge, part of a dam that runs beside Willett Pond, was closed last August because of extensive cracking in the concrete and after the piers holding sections of the bridge were undermined by water.

However, the spillway, which allows excess water to flow out of the pond and was built as part of the structure, is owned by a subsidiary of the Neponset River Watershed Association, an environmental nonprofit. If the bridge is fixed, the spillway will need to be upgraded as well, said Ian Cooke, executive director of the association. But the association does not have the money for the work, he said.

Jonathan Carlisle, spokesman for the state Highway Department, said the agency would normally fix a municipally owned bridge such as the one in Walpole. But, in this case, the town only has a right-of-way over the spillway and does not own it.

So, what happens next? Neither Cooke nor Carlisle is sure.

''That's anyone's guess," said Carlisle. ''There's no resolution in sight," although the state is willing to work with the different parties on a solution, he said.

One thing is certain: The delay won't make the bridge cheaper to fix.

In West Bridgewater, the South Street bridge lies buckled over the black, swirling waters of the Town River a year after the span was blocked off after rising waters washed out a supporting layer of hard-packed gravel.

Local officials are hoping that construction of a new bridge will begin this fall or next spring, said Town Administrator Elizabeth D. Faricy. She said a public hearing on the bridge design is planned for April 24.

Town officials had hoped to have the replacement bridge by this summer. The new structure is expected to cost about $1 million, according to the state.

Hull's Straits Pond bridge has all the others beat when it comes to obstacles encountered. The project has seen nearly every complication conceivable -- including major environmental concerns, because the structure involves tidal gates.

The bridge touches Hull, Hingham, and Cohasset, so local boards in all three towns need to sign off on everything. Four major utilities -- telephone, water, gas, and sewer -- run across the span. About a half-dozen permits are still needed, from local conservation commissions to the Army Corps of Engineers.

Meanwhile, the structure, also known as the West Corner Culvert, is too short to be officially considered a bridge; at 12 feet, it is 8 feet short of the minimum length to qualify for state highway money. This has further complicated matters, and plans for the culvert remain far from complete.

The state Highway Department, which normally is not involved in work on nonqualifying bridges, was pulled into the project within the past month because of political pressure -- but Carlisle said the agency's exact involvement remains unclear.

''The consensus is, we will help in some capacity," he said.

He said it is not clear when work would start or be completed, although town officials and others expect the new structure to be finished in the spring of 2008.

That would be some eight years after the bridge, built in 1908, was reported to be in poor condition and neighbors began clamoring for improvements.

A 2000 state highway report described exposed steel poking from the reinforced roof of the bridge and stones shifting in the supporting walls, or missing. Neighbors also complained of water stagnating under the span, creating environmental problems. Tidal gates, built as part of the bridge, are supposed to let the tides flush Straits Pond, a 92-acre coastal salt pond. But neighbors said the gates did not let enough water in or out, so in the summer they would be plagued by unsightly algae blooms and swarms of midges.

Area residents formed the Straits Pond Watershed Association to push for a new bridge and better tidal gates, said its president, Lawry Reid. The group handed out fliers and held public meetings. State Representative Garrett J. Bradley, a Hingham Democrat, called it ''by far the most organized, determined, and effective citizens' group I've ever been involved with."

Eventually, the project began to move forward with political help at the state and federal levels. The three towns agreed to share the cost for a design contract; US Representative William Delahunt helped pass an $800,000 line item in the federal budget for the project; and state Senator Robert L. Hedlund, a Weymouth Republican, and Bradley helped push a $1 million authorization in the Legislature for the work. The state money has been authorized, but it is not certain that it will be appropriated.

Said Reid, ''You have to be so bloody persistent over such a long period of time, it's incredible."

Matt Carroll can be reached at mcarroll@globe.com.

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