Spring means the start of road work, and the state Department of Transportation has an estimated $350 million in construction planned this year for highways and bridges in Allegheny County.

The work, of course, will mean delays or detours for motorists, so PennDOT requests drivers to allow extra time, slow down and be patient.

Here are some of the projects planned for state routes and bridges in the northern suburbs:

• Route 28: A $35.8 million, 6.8-mile project was started a year ago, to improve 17 bridges, patch concrete and resurface Route 28 in both directions from south of the Harmarville interchange to the Russellton exit; create a third northbound lane from the Harmarville interchange to Pittsburgh Mills; and build two noise walls in O'Hara, Harmar, Springdale, Frazer and East Deer.

Construction will conclude in late fall.

Around-the-clock lane closures on northbound Route 28 currently in place will continue through early June; southbound restrictions are expected to occur only during off-peak hours at this time.

PennDOT also started an $8.5 million project to address the rock fall area and improve safety on southbound Route 28, which will be completed late this year.

Blasting was halted April 15 after debris unexpectedly blocked traffic on southbound lanes. Blasting will resume at 8 a.m. Saturday, weather permitting. Traffic will be stopped in both directions at 7:55 a.m. and the delay is expected to last 15 minutes.

• Interstate 79 Neville Island to I-279 Parkway North: The $61 million improvement project will address 6.6 miles of one of the roughest sections of interstate remaining in Pennsylvania.

The project started last summer and improved the northbound lanes; this year's effort will address the southbound lanes.

Preliminary work is under way with the crossover of southbound traffic to the northbound lanes scheduled this week.

When the project is completed late in the year, all of Interstate 79 in Allegheny County will have been reconstructed or resurfaced.

The work also includes ramp improvements, drainage, guide rail, shoulders, highway lighting, signing and pavement markings, Intelligent Transportation System expansion and installation, rehabilitation of bridge structures and culverts and other work.

• Route 28 to I-279 missing ramp: PennDOT started work late last year on a $7.9 million project that will construct a new ramp allowing southbound Route 28 traffic to travel directly onto I-279 south. The new ramp, when completed, will allow free-flowing traffic between southbound Route 28 and southbound I-279.

The project will be finished in September. Various ramp and shoulder restrictions will occur on roadways in the project area on Pittsburgh's North Side.

• I-279 Parkway North: This estimated $10 million to $20 million project will begin next month to improve the Parkway North from the Fort Duquesne Bridge to Camp Horne Road, Exit 15. Work will also occur on the High Occupancy Vehicle lanes, which will require closures.

The project includes concrete pavement patching, drainage, guide rail, signs, pavement markings, bridge rehabilitation and other miscellaneous construction. Lane closures and detours should be expected. Work will conclude early next year.

• Route 28 Heinz Wall repairs: Construction will take place off the shoulder of northbound Route 28 between Chestnut Street and Heinz Street in Pittsburgh.

The project includes reinforcing the existing mechanically stabilized earth wall with a soldier beam and lagging wall.

Some ramp and lane closures will be necessary. Construction will begin next month and conclude early next year. Estimated cost: $2 million to $3 million.

• I-579 Crosstown Boulevard: The $5.27 million project includes rehabilitation, milling, concrete patching, structural repairs, signs, pavement markings and bituminous overlay on various ramps and I-579 from the intersection with Route 3069, Liberty Avenue, to the Veterans Bridge in Pittsburgh.

The project will use temporary ramp detours with night and weekend lane closures. The project began last month and will conclude early next year.

• Route 28 Etna Interchange Phase IV: The next step in PennDOT's effort to improve Route 28 in Etna area will begin in late July.

The project will include bituminous and concrete pavement reconstruction, approach roadway widening, drainage, guide rail, curb, shoulders, highway lighting, signs, pavement marking, bridge reconstruction, wall construction, and other improvements on 2.33 miles of Route 28 in the interchange area south of Route 8, to approximately 400 feet north of Route 1005, Highland Park Bridge.

Motorists should expect lane closures and possible ramp detours. Construction will conclude in late October 2009. Estimated cost: $10 million to $40 million.

• Route 19, Marshall Avenue: Mill and overlay, base repair and utility adjustments, minimal drainage improvements from Route 3921 to Brighton Road in Pittsburgh.

• Route 3919, Chateau Street: Mill and overlay from Faulsey Way to Nixon Street in Pittsburgh.

• Route 3931, Marshall Avenue: Mill and overlay, base repair and utility adjustments, minimal drainage improvements from McCook Street to Route 19 in Pittsburgh.

• Route 4011, Rochester Road: Mill and overlay including existing shoulders from Route 4049, Nicholson Road, to Route 4043, Camp Meeting Road, in Franklin Park.

• Route 4019, Mount Royal Boulevard: Mill and overlay, base repair and utility adjustments from Ferguson Road to Route 8, William Flynn Highway, in Hampton.

• Route 4019, Mount Royal Boulevard: Mill and overlay, base repair and utility adjustments, minimal drainage from Iola Avenue to Elfinwild Road in Shaler.

• Route 4036, Ambridge Avenue/Big Sewickley Creek Road: Mill and overlay, including existing shoulders from Beaver Street to Hitzel Hill Road in Economy, Leetsdale, Bell Acres and Leet.

• Route 4052, Warrendale Bayne Road: mill and overlay, including existing shoulders and minor drainage improvements from Mingo Road to Tech 21 Drive in Marshall.

District 11 will also perform numerous bridge preservation projects around the county. For more information, see www.state.pa.us/district11.

• Route 8/62nd Street Bridge: This $6.6 million project to preserve and improve the Robert D. Fleming Bridge that carries Route 8 over the Allegheny River in Pittsburgh, Etna and Sharpsburg, started construction early last month.

The work involves numerous improvements, including replacing precast parapets, deck joint replacement and resealing, deteriorated concrete repairs, zone painting, approach roadway work, highway lighting, pavement markings and other miscellaneous construction.

The southbound lanes of the bridge will be closed to all traffic through late June. The project will conclude in November.

• Route 1010 Harts Run Road Bridge: The project will replace the bridge that carries Route 1010, Hart's Run Road, over a branch of Hart's Run in Hampton. A detour will be necessary during construction.

The project will begin in November and will conclude in October 2009. Estimated cost: $1 million.