The state governor has signed a bill in Alaska forming a Knik Arm Bridge and Toll Authority (KABTA). The state is committing to $500k/year through 2009 to support... KABTA's job is to build and operate a $1.9 billion bridge an approach roads. MORE
The state governor has signed a bill in Alaska forming a Knik Arm Bridge and Toll Authority (KABTA). The state is committing to $500k/year through 2009 to support KABTA operations. The governor appoints all five of its directors who serve staggered terms of 5-years and can only be removed “for cause.”
KABTA's job is to build and operate a $1.9 billion bridge an approach roads.
''It's going to be a long-lasting investment in Alaska's future,'' Gov Frank Murkowski said at a ceremony signing the toll authority into existence. "The bridge will
unite Anchorage and the Mat-Su Borough to enable growth to take place
throughout southcentral Alaska.”
A proposed Knik Arm bridge is Anchorage’s “harbor bridge.” Knik Arm is the northerly of two arms of the long Cook inlet, that form a west-facing promontory on which the city of Anchorage is lodged. Like Sydney Harbor, Anchorage was discovered in the 1780s by the British explorer Captain James Cook after whom the grand inlet was named.
Anchorage has Alaska’s major port and airport, and it is the remote state’s only metro area as classified by the Census Bureau (260k pop). [Juneau the state capital is located in a Gaza-like strip of American territory to the south alongside Canada and houses a mere 30k people.]
Anchorage is strangely something of an “island” isolated from the bulk of the state by the two arms of the Cook Inlet on three sides and by mountains to the east. The downtown is flanked by the civil airport to the west and by Elmendorf Air Force Base and the Army’s Fort Richardson to the northeast. Knik Arm Bridge is proposed as providing access to Point MacKenzie and the open land of Matanuska-Susitna Borough 4km (2.5mi) across the waters to the north, as well as a more direct connection to AK-3, the major road to the inland and Fairbanks.
There have been many studies of this bridge. They have foundered on cost plus the military’s need to keep traffic away from lines of flight and long range antenna of the Elmendorf AFB.
The bridge has to span about 4.1km (2.6mi) of the Knik Arm channel. On the now planned location it is downstream of the port of Anchorage, so it only has to provide clearance for barges.
Foundation conditions are difficult and the area has major earthquake risk, which makes it similar to major bridges in Seattle and San Francisco. The approach roads on the Anchorage side are complicated and no corridor has been reserved.
A “Knik Arm Crossing Engineering Feasibility and Cost Estimate Update” has been completed but as yet no traffic and revenue study. The Update by Parsons Brinck builds on a DEIS of 1984 which was not able to choose between two different locations and route connections. There had been earlier crossing studies in 1955 and 1975.
The PB report denies choosing a preferred alignment but then works with a hybrid route with a 4.5km (3mi) approach road following the coast, skirting Elmendorf AFB, then curving over the channel, not unlike the Coronado bridge in the San Diego area.
On the northside there is to be a Mat-Su connecting road, making a facility almost 60km (37mi) in length overall. The shortest, most direct route from the downtown over the channel goes through much deeper water and more difficult foundations, and since it would be upstream of the port, would have to be high. Other routes to downstream of the port go through one or other of the military bases, and lose functionality by being more circuitous.
PB envisages a precast concrete box girder bridge with about 25 to 20 spans averaging between 150m (500ft) and 215m (700ft). The new Benecia-Martinez and Oakland span of the Bay Bridge are similar in per span lengths. The Confederation bridge New Brunswick to Prince Edward Island has 250m (820ft) spans. The piers will be on large 2.5m to 3m (8ft-10ft) diameter, 75mm thick (3in) piles requiring hammers of 80MN (18k kips) or close to the strongest in the world. There are huge glacial boulders down there. The PB report complains about the paucity of subsurface geotechnical data (p2-6) and the uncertainty about the location and extent of a treacherous clay layer with low bearing strength. And it says strong (8 knot) currents, 15m (48ft) tidal variations year-round in the Knik Arm and winter ice and winds make construction tough.
PB says it will be worth considering one or more "extradosed" cable stay spans to reduce piers and pier costs in deeper water.
Of the bridge itself the PB report says: "The ultimate feasibility of a Knik Arm Crossing is not in doubt. In overall scale, the bridge is comparable to other structures built in the past decade. The bridge, however, will have to face a possibly unique combination of environmental conditions: cold weather, high seismicity, ice loads, and a large tidal range. But the meteorological conditions and seismicity are no more severe than those encountered elsewhere. The ice loads and tidal range combined may make a crossing of Knik Arm unique. But the ice loads are of reasonable magnitude; what is needed is an innovative design that will manage the ice effectively." (p3-26)
Two tunnel designs were looked at. They turn out to be even more difficult, and expensive, than the bridge.
On the southern approach road from downtown Anchorage there is there is 1340m (4400ft) of bridging over local streets and port facilities. Also there will be a 215m (700ft) doubledeck tunnel built through Government Hill. This area dropped 6m (20ft) vertically and moved laterally 15m (50ft) during the mag-9.2 earthquake of 1964! Chances of a similar magnitude quake at the bridge site are put at 13% for its design life of 100 years.
The PB "Upate" costs the 4115m (13.5k ft) long bridge at $1,536m, and the approach roads at $383m for a total design and construction cost of $1,919m. Cost could be reduced by $375m by building 1.2km (4k ft) of the bridge in tidal flats as causeway but this might not pass environmental muster because of interference with tidal currents. A tunnel - doubledeck in a single 14.6m (48ft) bored tube 4725m (15.5k ft) - would be $923m more than the full bridge. Adding a railroad track to the bridge would add $348m.
This is one expensive project for a city of only 300k people!
Rationale
No way can this project be justified in terms of satisfying traffic needs! The bridge is only justifiable if it is considered important to use large amounts of taxpayer money to foster economic development. It will help the Alaska’s major city break the bounds of its confined location and expand to the north, by providing 5 to 10-minute trips to the wide open spaces of Mat-Su borough across the Inlet. Trips to that area presently involve circuitous travel of about 100km (60mi) around the end of the inlet, and about 75 to 90 minutes. So few such trips are made, and development there is scant.
Rep Don Young, chair of the House transport committee says the bridge will help the Alaskan economy by allowing more efficient access to the port of Anchorage and the airport. But not sufficiently to generate a revenue stream to support the project! The port and airport might relocate to Point Mackenzie in the future with the bridge in place.
It is to be a largely tax-funded, but toll-assisted project perhaps in a ratio of about ten tax-$s to one toll-$. Project cost is probably $2.3 billion. Likely traffic is of the order of 20k to 35k/day depending on the toll. At $5 and $3 it would generate gross $30m to $40m, enough to support a bridge costing $250m to $300m?
Traffic forecasts made in 1984 for Anchorage in 2000 have turned out to be high. Employment in the area is only 145k vs 173k assumed when traffic was forecast for the bridge in 1985. If the bridge had been built then its revenues would have fallen way short of projections. At the time a 2x3-lane bridge was contemplated. PB says all the plausible forecasts now support 2x2-lanes.
The Update notes that the toll revenues from the bridge are a special challenge for forecasters to model because of their dependence on induced development on the north shore. (p6-17)
A full environmental impact statement is now starting and could take up to three years for a record of decision mid 2006. Construction would take about four years for a 2010 opening. (contact James Armstrong: armstrongjj@ci.anchorage.ak.us) TRnews 2003-07-02
