By Cara Mitchell and Tim McCall
This October marked three years since the I-5 Steilacoom-DuPont Road to Thorne Lane Corridor Improvements projects began. While the contractor is wrapping things up, our traffic engineers are looking at how the addition of a new northbound and southbound high occupancy vehicle lane has changed traveling through this corridor.
In July 2021, when the northbound HOV lane first opened near 41st Division Drive at JBLM to Gravelly Lake Drive in Lakewood, drivers told us they saw an immediate improvement in drive time. The daily backups that previously occurred during the commute hours approaching 41st Division Drive vanished.
Three months later, an early look at the traffic data shows big benefits for travelers.
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| I-5 with HOV lanes open at Berkeley Street near JBLM and Lakewood's Tillicum neighborhood. |
Ways to look at traffic data
Traffic data comes in different forms. We can look at actual traffic volumes or look at traffic density or congestion.
Because the corridor has been under construction for three years, pulling accurate traffic data that uses traffic volumes can be misleading. Construction tends to skew that data because there are either reduced or shifted lanes that traffic sensors can't capture. This happens in large part because the instruments that we use to capture that data were disrupted or temporarily taken offline during construction.
The type of data that we can look at with a fair amount of confidence is density or congestion. That is what these heat maps show, and it reflects the feedback that travelers through the corridor are experiencing.
What these colorful maps represent
The colors in these density maps represent traffic congestion at different locations at different times.
- Red and black indicate that things are slow going.
- Yellow indicates some slowdowns.
- Green is free flowing with no backups or delays.
The locations are listed on the right side of the map. The time of day is listed at the bottom.
The data chosen for the heat maps shown below were Tuesday through Thursday averages in the month of September for year 2019 and 2021. We are not using 2020 data due to the low traffic volumes associated with the Covid-19 pandemic.
Northbound I-5 traffic density in 2019 and 2021
In 2019, before the HOV lanes opened, travelers on northbound I-5 frequently saw heavy traffic volumes during the afternoon commute approaching JBLM Main Gate through Berkeley Street. The morning commute also saw frequent congestion, although not quite as dense as the afternoon, starting from SR 510 in Thurston County north to Berkeley Street in Lakewood.
The data from 2021 shows during the afternoon northbound commute the previous congestion disappeared, while the morning commute is not as heavy.
Southbound I-5
The story for southbound I-5 is encouraging.
In 2019, morning commuters on southbound I-5 saw very little congestion. If slowdowns happened, it was often seen approaching Berkeley Street and JBLM Main Gate. The afternoon commute painted a different story. Heavy traffic volumes typically would begin at 3 p.m. near SR 512 and continue south eight miles into DuPont.
The new southbound HOV lane made previous morning congestion disappear. The afternoon commute has been shortened. The congestion naturally moved further south. The graph above shows an afternoon commute starting at 4 p.m. near JBLM Main Gate. We still see some congestion during the afternoon commute near Berkeley, but it's for a shorter duration than before.
The congestion moved
Yes, in the afternoon on southbound I-5, the location where we see heavier traffic volumes has moved further south. One big reason for this is because the HOV lane and new auxiliary lane ends just south of 41st Division Drive – for now. The next phase of construction, scheduled to begin in 2023, will finish widening I-5 to Steilacoom-DuPont Road and extend the HOV lane a few miles south.
Many people ask why not widen I-5 further south past Mounts Road. It's something we are looking at, but right now there is no construction funding for it. We are aware of the congestion through Nisqually. In fact, these heat maps capture it. The cost to modify I-5 through the Nisqually Delta would be significant and require legislative action.
Project history
The I-5 Mounts Road to Thorne Lane Corridor Improvements Project was funded in 2015 by the State Legislature for $485 Million. That funding was spread out over 10 years and broken up into four separate construction projects. Traffic patterns, volumes and populations can easily fluctuate over 10 years. Just as the price of land has gone up for developers and homeowners, it goes up for construction projects too. It's a big reason why we look at the resources available to us. We use practical solutions, which is a process that solves problems and needs as quickly and inexpensively as possible, to help solve traffic problems. We made the choice to build HOV lanes – a traffic management tool that moves people rather than individual vehicles.
Some of our earliest traffic studies from the 1990s told us that HOV lanes on I-5 were going to be a necessity in the years ahead through Pierce County. Finding funding for improvements like this isn't easy, which is why when it is allocated, we have to design and build something that will take us as far into the future as we possibly can see.
Traffic patterns and data are always changing
We think it's important to mention that traffic patterns and volumes fluctuate daily. It may not be obvious to you when you're behind the wheel, but our traffic engineers see it. For example, weekdays see heavier traffic volumes at different times of the day than the weekends. Anyone who has endured a Friday afternoon commute on southbound I-5 knows just how difficult that journey can be. Likewise, traffic patterns change in the summer months when schools are on break and the summer travel season is in full swing. It's important for us to monitor this because it will help determine when a contractor can close lanes for a construction project, or when a good time is for maintenance crews to go inspect a bridge and not have a lane closure cause long backups tor travelers.
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