Pavement - Projects & progress
Concrete pavement preservation expected to need as much as $2.69 billion through 2045
WSDOT estimates it will need $2.26 billion-$2.69 billion for concrete preservation through 2045—an average of between $94 million-$112 million annually. This estimate, which does not account for inflation, reflects an average annual need to reconstruct 50 lane miles of concrete pavement and rehabilitate 45 lane miles.
WSDOT manages approximately 2,080 lane-miles of concrete pavement, most of which were constructed in the 1950s and 1960s. This pavement has far exceeded its original design life and has carried several times the traffic load than originally anticipated. More than 65% of WSDOT's lane miles (1,365) are over 40 years old and almost half of these lane miles (638) have never been improved.
WSDOT's lowest-cost network preservation strategy requires that a reasonable number of lane miles of concrete pavement be reconstructed each year on a continuing basis. The average annual requirement was 50 reconstruction lane miles and 45 triage lane miles over a 30-year period (2016-2045). However, seven years have passed, and WSDOT has reconstructed about 28 lane miles due to constrained pavement preservation funds.
Most of the concrete network must be reconstructed within the next 20 years to avoid the risks of unexpected failures in critical areas and more costly construction. The concrete pavement most needing reconstruction is in highly congested areas (primarily in King County). These areas present additional challenges due to the complicated nature of the projects and the short work windows available because of traffic delay concerns.
Due to the age of the roadway, WSDOT must reconstruct I-5 from milepost 155 (near Southcenter) to milepost 178 (near the King/Snohomish county line), this amounts to approximately 200 lane miles over the next 15 years. Unavoidable traffic impacts will be significant and must be coordinated with bridge and barrier construction occurring in the same vicinity. This scenario will be repeated in these critical transportation areas every year.
Seventy lane miles of concrete reconstruction per year is needed for the next 20 years. Of that total, 25 lane miles per year are in critical congestion areas, which will involve extensive traffic control and construction difficulties.
This work is in addition to 45 lane miles per year of triage projects, which are needed to extend life so that reconstruction can be delayed for 10 to 15 years.
WSDOT increases asphalt density to extend pavement life, makes most of funding
To make the most of available funding, WSDOT continues to find ways to increase the lifespan of pavement. In Washington, asphalt pavement lasts an average of 14 years before needing rehabilitation. If the average pavement life is extended by one year, the state can save $1,200 per lane mile in rehabilitation costs.
WSDOT in collaboration with the Washington Asphalt Pavement Association developed new standards for asphalt density to increase the life of asphalt pavement.
WSDOT's specification requirement for pavement density has gradually increased from 91% in 2016 to 92% in 2019, average densities have remained above the target by steadily increasing from 93.3% in 2016 to 94.0% in 2019. This 0.7 percentage point increase in average density should provide an additional year of pavement life. A 1% increase in density can increase asphalt pavement life by approximately 10%.
WSDOT implemented the last phase of the increased minimum density specification, and expects to see additional improvements in pavement density. Through this process, WSDOT plans to gain another year of pavement life for a total of two years.
WSDOT monitors pavement by using its standard practices of rating roughness, cracking, and rutting for all state-owned pavement. The agency uses this data to ensure pavement can be rehabilitated at the most cost-effective time—pending adequate funding—and will provide data to measure the effectiveness of the density changes.
WSDOT successfully tests precast concrete pavement
In spring 2019, WSDOT conducted a trial installation of precast concrete pavement on I-90 near Preston. The trial results showed that precast concrete could be a viable option for locations where higher traffic volumes make it impractical to close roads for longer periods to pour conventional concrete.
Slabs of precast pavement are fabricated offsite and then trucked to the repaving site for placement. The process costs more than conventional concrete pavement (the precast concrete pavement itself costs three times as much as conventional concrete, before accounting for other project costs such as labor) but provides an alternative for high-traffic locations where closing the road for long impacts on large numbers of road users.
In conventional concrete paving, the concrete must harden before vehicles can travel on the new pavement. Waiting for the concrete to harden contributes substantially to the duration of road closures. With conventional concrete paving, the road must be closed for at least a weekend (Friday night through Monday morning) while the concrete hardens. Precast concrete can be installed during overnight lane closures, resulting in no traffic disruption during peak travel times.
WSDOT's first crack, seat and overlay concrete reconstruction project performing well at eight-year mark
In 2011, WSDOT completed its first project using the crack, seat and asphalt overlay method on Interstate 5 in Skagit County. This project restored 12.5 miles of divided highway from Joe Leary Slough to Nulle Road. The project saved more than 38% in initial construction costs and is expected to save at least 23% in life-cycle costs over a 50-year period compared to a conventional concrete replacement or asphalt replacement.
Prior to the crack, seat and overlay, this section of I-5 was performing poorly. The joints in the concrete pavement were uneven, causing a rough ride. In 1993, the original rough concrete pavement was overlaid with hot mix asphalt to restore the smoothness of the surface. After only a few years in service, cracks and joints in the concrete reflected through the new HMA overlay and the roughness began to increase once again.
In contrast to the original HMA overlay, the crack and seat with asphalt overlay pavement was still in very good condition after eight years of service. As of 2019, reflective cracking had not reappeared, and the pavement was very smooth. The success of this project ensures that the pavement on this section of Interstate 5 will remain smooth and that future preservation costs can be kept low.
Concrete reconstruction methods at WSDOT
- Crack and Seat with Asphalt Overlay
Cost: $900,000 per lane mile
Longevity: 15 to 20 years
Fractures existing concrete pavement, turning it into a stable base for a thick layer of new asphalt pavement
- Asphalt Replacement
Cost: $1.3 million per lane mile
Longevity: 15 to 20 years
Removes the concrete slab and subbase, and lays new asphalt pavement
- Unbonded Concrete Overlay
Cost: $1.5-$2 million per lane mile
Longevity: 50 years
Places a thin layer of asphalt on top of the existing roadway, followed by a full-depth concrete overlay on top of the new asphalt
- Concrete Replacement
Cost: $2.5-$3.5 million per lane mile
Longevity: 50 years
Removes the existing concrete slab and subbase, and replaces it with a new, thicker slab. Used when an existing decades-old slab is not thick enough for current traffic levels
Note: Costs and longevity are approximations.
Concrete pavement preservation expected to need as much as $2.64 billion through 2049
In 2018, WSDOT estimated that it will need a total of $2.25 billion to $2.64 billion for concrete preservation through 2049, or $75 million to $88 million annually for the next 30 years. This estimate, which does not account for inflation, reflects an average annual need to reconstruct 41 lane miles of concrete pavement and rehabilitate 45 lane miles.
Much of WSDOT's pavement was constructed as part of the interstate highway construction program in the 1960s and 1970s, when concrete roadways were designed to last for about 20 years. WSDOT has been able to use a variety of rehabilitation treatments such as dowel bar retrofit, diamond grinding and selective slab replacement to extend the life of its concrete pavement. These rehabilitation treatments typically cost $400,000 to $800,000 per lane mile, and can extend pavement life by 10 to 15 years.
Rehabilitation cannot extend the life of concrete pavement indefinitely. As its condition declines, pavement becomes rougher, unexpected panel failures become more common, and rehabilitation becomes less cost effective. WSDOT estimates that most of its concrete pavement will reach the point where rehabilitation is no longer cost effective between the ages of 60 and 70 years. Concrete reconstruction costs between $900,000 and $3.5 million per lane mile, and can be done using one of four methods.
WSDOT manages 2,020 lane miles of concrete pavement (excluding bridge decks), of which 1,212 lane miles (60%) are over 40 years old and 734 lane miles (36%) have never been repaired. The agency's never repaired concrete pavement has an average age of 43 years.
Estimated cumulative savings from resurfacing asphalt pavement with chip seal pass $120 million in 2017
In 2017, WSDOT's estimated cumulative savings from resurfacing asphalt roads with chip seal surfacing (also known as Bituminous Surface Treatment, or BST) passed $120 million. Under this Practical Solutions effort, the agency has converted almost 2,300 lane miles of asphalt pavement to chip seal since 2010—over three-quarters of the 3,000 lane miles planned. Approximately 36.7% of WSDOT's pavement network is now made up of chip seal pavement.
Roads resurfaced with asphalt last about twice as long as those resurfaced with chip seal, but the cost of chip seal resurfacing is only about one-fifth the cost of asphalt resurfacing. WSDOT estimates that it saves approximately $13,000 per year for each lane mile of asphalt pavement that is resurfaced with chip seal.
Because of this substantial savings, WSDOT has prioritized resurfacing asphalt pavement with chip seal where appropriate (roads with average daily traffic over 10,000 vehicles, roads in urban areas and roads on which trucks frequently make turns are generally not appropriate for chip seal resurfacing).
WSDOT expects to finish converting the remaining 700 lane miles by 2024. Once all 3,000 lane miles have been converted to chip seal, the agency expects to save $40 million annually. The progress of the conversion effort is shown in the graph on p. 15. This conversion process will take WSDOT's pavement network from 25% chip seal in 2010 to 40% chip seal in 2024.