Room for public participation in interchange design

My turn

Posted: Sunday, June 17, 2001

As a final action prior to adopting the Area Wide Transportation Plan (AWTP), the Transportation Steering Committee (TSC) chose to delete the reference to "construction" of Egan Drive interchanges. The AWTP, as adopted by the TSC, includes "design" of interchanges but does not include "construction" of these facilities.

At the Planning Commission the term "construction" was included in the recommendations to the Assembly so that the AWTP would read "design and construction" of interchanges on Egan Drive, assuming the Assembly adopts the Planning Commission's recommendations.

As a transportation planner, highway designer and professional engineer I do not believe that the inclusion nor omission of "and construction" in the AWTP makes a practical difference. However, I do believe that there may be justifications for omitting the phrase "and construction."

From a practical standpoint, design of the interchanges, including environmental considerations, public participation and right-of-way acquisition will consume five years or more. The AWTP should be updated by 2005, using the horizon year 2025. If transportation plans are not updated every five years they become stale and are of little practical value. This update will require finalization of the computer model that was started during development of the current AWTP.

Transportation demand management (TDM) measures should be in place and operating in sufficient time for the results to be included in the 2025 AWTP. Using the model and the results of the TDM measures, the 2025 AWTP should clearly show 1) whether interchanges are needed, 2) where the first interchanges should be constructed based on need and 3) where the second channel crossing should be located based on traffic service. The interchanges at Vanderbilt Hill, Sunny Point and Yandukin should not really be finalized until the location of the second crossing is determined.

If the 2025 AWTP indicates traffic changes that eliminate the need for interchanges, then the interchanges need not be built. On the other hand, if the demand continues to grow in spite of TDM, like some of us expect, then the designs will be completed, including permits, environmental documents and public participation, and construction can begin in 2005.

Omitting "and construction" from the AWTP will also provide ample time for the general public to recognize the need for interchanges, assuming the traffic demand continues to exist. There is also a need for extensive public participation in the design of the interchanges. As an engineer who has designed dozens of interchanges in rural and urban areas, I know that many aspects of interchange design are technical in nature and cannot be subject to public whims. However, the are many aspects of interchange design that lend themselves to public participation.

The basic interchange design is one of those aspects. There are three basic types of interchanges; cloverleaves, diamonds and single-point. The cloverleaf has large landscaped areas with graceful curving roadways. The interiors of the loops create open space and can be visually attractive. On the other hand, a cloverleaf requires considerable area and is consequently described as having a large "footprint."

The standard diamond interchange has a smaller footprint than a cloverleaf. However, this provides less area for open space and landscaping. Yet a standard diamond can be made attractive as there is considerable sloping earth to be landscaped.

The single-point interchange has the smallest footprint but is not as aesthetically appealing as the standard diamond. This is because to minimize the footprint more use is made of retaining walls and a bigger bridge structure. As a consequence, single-point interchanges are usually restricted to urban areas where the cost of rights-of-way are so high that they off-set the higher costs associated with retaining walls and mega-structures.

While costs must be considered, the public should have input into which types of interchanges they wish at each location. Too often the desire to get to construction immediately restricts public input to a few legally mandated sessions. Multiple sessions in which the technical aspects of interchange design are explained and where designers listen to the general public where discretion can be exercised is beneficial to all.

The five-year period between adoption of the current AWTP and the 2025 update will allow time for design, public input and environmental documents. This five-year period will exist whether the AWTP includes the term "and construction" or not. Therefore, it does not seem to be a matter for extensive public debate and the omission may make those dubious of the need for interchanges more comfortable with the idea.

There is one caveat to this position; that is that the CBJ Assembly makes sure that work begins immediately on the 2025 update to the AWTP!

Roger W. Allington is a consulting traffic and transportation engineer who lives in Juneau.



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