Bridge costs considered

April 17, 2005

DAWN De BUSK/Frontiersman reporter

Knik Arm Bridge and Toll Authority members hear a lot of questions regarding how much the toll will be to drive across the proposed bridge.

This week, KABATA's executive director, Darryl Jordan, said he finds it hard to come up with a monetary amount for that fee.

However, the type of material used in bridge construction would likely dictate the cost of the toll, he said. For example, if KABATA selects a steel bridge design over a concrete structure, the toll would be higher because the costlier steel requires more maintenance than concrete.

He said several other factors will

help set the toll amount. One major determining component will be the cost of maintenance. Essentially, the toll was set up so the bridge would generate its own maintenance funding.

Another factor is how much the federal and state government are willing to reimburse KABATA for the project. Utility companies will also supply additional income if they choose to use the bridge as a corridor rather than burying lines under water, Jordan said.

How much money KABATA must borrow to complete the project and how much interest is applied to the loan will also affect how many dollars drivers will be handing to toll bridge booth attendants.

KABATA hired the finance company Wilbur Smith Associates, to help the authority get a low interest rate from the bank. Wilbur Smith Associates deals with toll and revenue forecasting.

Studies done about a decade ago showed that when the toll went from $2 to $3, traffic decreased by 10 percent, and when the toll was raised to $5, traffic dropped by 50 percent.

Those studies are older, however, so KABATA remedied that problem by conducting a household survey via phone last month. One of the questions asked was how much people would be willing to pay at the toll booth.

Personnel doing the study have not analyzed the data yet.

Carl Seaver, of Wasilla, was raised in Michigan where big bridges are commonplace.

"If it's $3, I'll pay it. Who drives from Anchorage to Palmer for $3? The price of gas has gone up," he said, adding that the toll amount will probably have to reflect inflation.

The cost of the project, which has been estimated between $400 and $600 million, includes construction of the bridge structure and its west and east approaches. Those cost projections account for inflation through 2010. The cost doesn't include maintaining the bridge or improving any roads tying into the bridge, Jordan said.

Engineers estimate the bridge will be 7,000 to 12,000 feet long, depending on whether a skewed or perpendicular alignment is adopted as part of the design.

During the early stages of the design process, KABATA toyed with the idea of the three-lane bridge, with one lane of traffic being reversed to accommodate the direction most traffic travels during certain hours.

"We can handle a high volume of traffic on the bridge because no additional traffic enters from the side, just at the toll booths," Jordan said.

The east and west approaches would be four-lane roadway, approximately 80 feet wide with shoulders.

Once a design becomes more specific - especially whether the bridge will be concrete or steel - the price will also be easier to pin down.

As far as aesthetics are concerned, conceptual drawings revealed a white concrete bridge and a black steel bridge spanning Knik Arm.

A concrete bridge will not only be less expensive in terms of material costs and maintenance, but it will provide more local hire. KABATA would build a fabrication yard on the Mat-Su side, which will provide Valley jobs during the construction phase.

The concrete bridge would include an interior corridor on either side of the vehicle lanes. This could provide a sheltered pedestrian walk-way or a utility corridor, said Jordan, adding that a pedestrian walkway is a multi-use system that could accommodate bicyclists.

One of the drawbacks of a concrete bridge occurs when expansion of the bridge becomes necessary.

"With pre-cast or pre-stressed concrete, once it's formed, it's much more difficult to expand. This is bad because if we want to build on, we'd have to build a new bridge," Jordan said.

Steel is much easier for expansion projects, he said.

According to the steel conceptual design, the multi-module walkway would be exposed to the outdoors so a person could see the pods of whales, ship activity, mountain ranges and sunsets and even ice floes during the winter.

"In the summer, it could be a huge tourist attraction," said Jordan, who said he would prefer enjoying the scenery from the outdoor walkway as opposed to walking along a pathway tucked inside a corridor.

Steel, which has skyrocketed in price, also requires a higher maintenance cost. During construction, it would need corrosion protection such as paint or anodes, or the steel would have to be galvanized. The steel would be fabricated in the Lower 48 and shipped to construction crews in the Valley.

Steel is lighter than concrete, so the steel design wouldn't require the heavier foundation piles necessary for the concrete version.

The biggest advantage of the steel is that it has greater flexibility during an earthquake, Jordan said.

The environmental impact studies will have no bearing on whether a steel or concrete bridge is erected. However, Jordan said, the bridge design must be able to absorb the shock of a large earthquake.

"There's no showstopper when it comes to seismic activity, but it's the number-one thing we have to design for," Jordan said. "Most bridges are designed for up-and-down load. Here in Alaska, an earthquake can add a sizable sideways load."

Seismic loading refers to the forces an earthquake would add to a bridge. The weight of the bridge and its potential traffic is multiplied by .55 or .45 to determine lateral forces.

Jordan said the seismic loading shapes the bridge design. Seismic loading is such a huge part of the picture that bridge designers won't have to take into account wind pressure, tidal pressure or ice floes. In other words, a bridge designed to withstand an earthquake would be capable of handling high winds or strong tides.

The Little Susitna River travels down the nearest fault in the Mat-Su - the Castle Mountain Fault. On the Anchorage side, the fault closest to the bridge would be the Border's Range Fault, which runs along the base of the Chugach Mountains.

"They're close. They're not far away," Jordan said. "But they're not under the Cook Inlet."