If you flew in or out of Portland International Airport (PDX) this summer you probably noticed that there has been quite a bit of street construction underway near the terminal building. Here’s what’s been happening.
The Port of Portland, KPFF and Kerr Contractors are nearing the end of a project to preserve and rehabilitate the pavement leading to and from PDX’s arrival and departure gates. Because of the overlap between the peak construction season and the peak travel season, this has been a high profile project for everyone involved. As an engineer at KPFF, I have had the opportunity to work on the planning, development and implementation efforts over the past year and a half.
Our team’s work began with building a 40 year life cycle cost analysis to compare the construction and maintenance costs associated with three options to extend the pavements service life: rehabilitation with an asphalt concrete inlay, reconstruction with asphalt concrete pavement and reconstruction with portland cement concrete pavement. Following selection of a preferred combination of work, we developed plans and specifications detailing the project, and we will continue to provide support until construction is completed in early October.
The following photos are from recent site visits and cover the major components of the work.
Lower Bus Lanes
Each day about 540 bus trips are made shuttling people from the PDX economy lots, to the terminal building and back again. The buses making these trips are big, double rear axle vehicles and they all follow the same route. Understandably, the asphalt pavement along this route had lived a difficult life. The buses’ weight combined with starting and stopping forces had lead to severe rutting in the pavement – so much so that it had begun shoving the adjacent curb and sidewalk.
Based on our life cycle cost analysis and existing pavement conditions, the team determined reconstruction with portland cement concrete pavement to be the best rehabilitation option in the bus lanes. The resulting roadway provides a more rigid platform for heavy bus loading, which should result in a more durable pavement structure.
Lower Passenger Lanes
Near the bus lanes is a separate roadway dedicated to carrying the thousands of passenger cars that visit the arrival gates each day. These lanes carry a high volume of traffic, but it is not heavy traffic, so pavement distress was limited to wear and minor cracking in the top surface.
Under typical conditions, asphalt concrete pavement fails from the top down. Loading creates small cracks in the top surface and these cracks gradually work their way down through the pavement. If the cracks reach the bottom of the pavement section, the pavement fails and must be replaced. However, if those responsible recognize that this cracking has begun, the corrective work can be limited to removing and replacing the top surface to the crack depth, resulting in a significant savings of both time and money.
During predesign work, the project geotechnical engineer determined that with proper top surface maintenance, the pavement section in this area will essentially never fail under passenger car loading. Such a design is called a “perpetual pavement.” As such, our life cycle cost analysis showed there to be a significant savings in using an asphalt concrete inlay here. The completed work involved removing and replacing approximately 2 inches of the existing pavement.
Upper Passenger Lanes
Traffic to and from the airport’s departure gates is carried on an elevated roadway that is split into two sections. The section furthest from the terminal building is used by taxis and other commercial traffic and exists entirely on a concrete bridge structure. This section was not included in the project and remains unchanged. The section nearest the building is used by all other passenger car departure traffic and is built partly on that same bridge and partly on the roof of the lower baggage claim area. Because it is constructed on top of an occupied space, the original construction of this roadway included a waterproofing membrane on top of the building, overlain by a layer of asphalt concrete pavement. The existing pavement and membrane were both at the end of their expected service lives and had begun to show signs of distress.
This past week, the contractor finished removing this existing pavement and waterproofing membrane and began preparing the surface to receive a new spray applied membrane. Spray applied waterproofing membranes are relatively new in the US and, in the right applications, offer superior performance in almost every respect when compared to more traditional products. After the new membrane is placed, the road will receive a layer of pavement. The completed roadway will look much the same as the original, but will have a renewed service life.
One of the project’s smallest but most visible changes involved removing the miniature stop signs that used to guard the airport’s raised crosswalks. These signs have long created a headache for both drivers and maintenance personnel. The new crosswalk delineation includes cross hatch striping and overhead “Stop for Pedestrians” signs.
So, it has been a busy summer at PDX. Pavement preservation work can create a temporary inconvenience from time to time, but streets are expensive and proper maintenance is a critical part of protecting our infrastructure investments. Hopefully this post has given you some insight into the work and the engineering behind this particular preservation project.