ACTT Workshop: Oregon
Paving The Way
Chapter 2: Project Details
2.1. Corridor Description
Oregon's Interstate freeway system performs a vital function in the movement of people and goods, with I-5 serving as the backbone for West Coast travel and the I-5/I-405 loop staking claim as the single most important transportation system in the State. The loop functions as the heart of the region's transportation system, connecting major community centers and providing access to National and regional transportation routes. The loop also provides access to the downtown Portland area on both sides of the Willamette River, which is important because downtown Portland serves as the cultural and civic center for the region and is home to about 20 percent of area employers.
What's more, the operational capacity of the I-5/I-405 freeway loop has proven vital to the overall function of Portland's transportation systems. Both the city of Portland and ODOT encourage the use of the freeways and highways for long-distance trips and local streets for short trips. However, because the freeway is comparatively fast and has numerous access points, many drivers use the freeway loop for local trips. At the same time, because some freeway connections are missing, many travelers making regional trips must use local streets. As a result, the I-405 system operates at or above capacity during much of the day.
To complicate matters further, little consideration was given to the impacts on the areas through which the freeway traveled when the loop was built. Simply put, communities were divided or destroyed to make room for the highway, ramp systems and associated parking facilities.
Since its construction in the 1960s, there has been minimal reconstruction work on the I-405 mainline: the majority of the work has focussed on the ramp systems and approaches. This is in spite of the fact that the continuously reinforced concrete (CRC) pavement on I-405 is the oldest on the State system and has outlasted its 20- to 25-year structural design life. (The CRC pavement begins at milepost 1.05 in the vicinity of SW 6th Avenue and ends at milepost 2.58 in the vicinity of NW Johnson Street.) There is no quantifiable way to determine how much longer the CRC pavement on the Interstate will survive. Typically, when CRC pavement begins to show signs of structural distress, it deteriorates rapidly.
2.2. Project Goals and Objectives
ODOT's objective for the I-405 pavement preservation project is to reduce construction time while giving motorists a high-quality product. In addition, ODOT wants to evaluate design options for the I-405 pavement preservation project in order to define funding needs for the next Statewide Transportation Improvement Program, or STIP. With that in mind, ODOT asked ACTT workshop to assist in that process by addressing the following issues:
- Maintaining traffic during construction with minimum disruption to the traveling public.
- Reducing cost by reducing overall construction time.
- Maintaining a safe work zone for workers and travelers.
- Minimizing delays introduced by ROW, utilities and light rail transit.
- Incorporating context-sensitive elements into the design strategy as appropriate.
- Balancing conflicting sub-standard system conditions with available funding limits.
Figure 1: Project Area
2.3. Proposed Improvements
A pavement rehabilitation strategy is needed to address I-405's out-of-date pavement and funding constraints prior to the failure of the system. Region scoping teams have estimated the cost to replace the CRC pavement at anywhere between $35 and $45 million. That far exceeds ODOT's existing pavement preservation funding limit of $10 million. ODOT attributes the variation in cost estimates to variable items such as utilities, ROW acquisition, storm-water, shoulder width, barrier treatment, overpass height clearance and constructability issues.
2.4. Project Background
Interstate 405, also known as the Stadium Freeway, is the western north-south route through downtown Portland. Figure 1 shows the Stadium Freeway in relationship to the Willamette River that divides downtown Portland. The CRC pavement on I-405 is 34 to 37 years old and has carried traffic volumes in excess of its design life expectancy, averaging between 44,000 and 62,500 vehicles one-way on a daily basis. ODOT has noted structural distresses, but the amount of distress is low given the age of the pavement. Computer-based modeling suggests that the CRC has no remaining life and should have begun failing long ago. Based on pavement wear in similar locations throughout the State, the CRC pavement on I-405 has structurally outlived any other CRC pavement and could fail at any time.
2.5. Project Challenges
Designed in the 1940s, I-405 and I-5 were built in the 1950s and 60s. The current design of the I-405 corridor mainline, ramps and surface streets contributes to the poor operation of the freeway loop system and is not sufficient for today's major traffic demands. Forced lane changes, abrupt and unexpected merges, short weaves and poorly spaced entrances and exits compound the problem.
Additionally, the design standards for Interstates have changed since the roadway was built. I-405 does not meet current standards with regard to ramp acceleration and deceleration lengths, spacing of interchanges and ramps, vertical clearances, horizontal clearances and sight distances.
What's more, no significant improvements to roadway capacity have been made since the Interstate system was constructed. With the travel demand beyond the current capacity of the freeway, congestion in the project corridor slows travel for many miles along other freeways and surface streets feeding into downtown Portland. This is most evident during the morning and afternoon rush hours.
The major challenges for the I-405 pavement project are as follows:
- Truck Traffic. Statistics show that truck traffic on I-405 accounts for over seven percent of the daily traffic volumes. With daily volumes of 125,500 vehicles in some areas, this equates to over 8,700 trucks a day.
- Multiple Major Traffic Movements. There are major interchanges with U.S. 26, OR 30, I-5 and Highway 99E within a very short distance. The weaving that occurs between these junctures influences traffic operations significantly.
- Balancing Transportation Needs with Local Access. There are over 40 entrance and exit ramps within the 4.21-mile project corridor. Current design standards for ramp spacing and weaving distances will not allow all of the existing entrance and exit ramps to remain.
- Constrained Right-of-Way. The I-405 corridor is highly developed, and ROW is limited by development, railroads and the Willamette River.
- Environmental Issues. There are over 200 potentially historic properties immediately adjacent to the Interstate. In addition, several protected species of birds nest along the Fremont Bridge at the northern end of the project area. Finally, the Willamette River, which receives all the storm-water runoff from the project area, is listed on the Superfund National Priority List (NPL).
- New Design Standards. The Interstate doe not meet current design standards for parameters such as horizontal and vertical clearances, lane and shoulder widths, acceleration/deceleration lanes, on-ramps, ramp spacing, sight distances, lane continuity, signage, median barriers and the ability to provide for incident management.
- Access & Traffic Handling During Construction. With so many employment centers and activity locations in the downtown area, constructability and access are an underlying concern.
- Affordability. ODOT is facing a funding shortfall and has not identified a funding source for the I-5/I-405 loop master planning effort. Developing an economic and efficient design that has the support of the community will be vital to moving towards construction.
- Urban Design. Because the I-405 project runs through the heart of downtown Portland, ODOT must consider urban design and landscape treatments to enhance the aesthetic quality of the freeway corridor.