Sonoma County's portion of the Marin-Sonoma Narrows widening project. See larger portions below.

Widening a 16-mile stretch of highway doesn’t sound like a big deal, but when that roadway is as complicated as the Novato Narrows, there is no quick fix. The $475 million Marin-Sonoma Narrows widening project began in April, 2013, and won’t be finished until 2016.

Representatives from Caltrans and the Sonoma County Transportation Authority recently took a drive through the project to answer questions and explain the construction that is causing agonizing delays between Petaluma Boulevard North (Old Redwood Highway) and Highway 37 in Novato. Here’s what they had to say.

Traffic has grown steadily over the years as a result of population growth and Sonoma County’s steadily growing tourism industry, which causes weekend gridlock. Bumper-to-bumper traffic heads north on Fridays and Saturdays, then returns south on Sundays.

The Narrows is the last four-lane stretch between Windsor and the Golden Gate Bridge, a remnant of days gone by with driveways and country roads that feed right into the highway. Portions are steep enough to slow big rigs and circuitous enough to block motorists’ views of traffic conditions ahead. The road also passes through two counties, which means any construction must be jointly planned and executed,  and it contains four bridges that had to be widened or replaced.

When the project is done, it will have made room for HOV lanes, rebuilt bridges that cross 101 and created one central interchange between Petaluma and Novato, eliminating access from the small farm roads and San Antonio Road. And although Highway 101 will have been widened to accommodate six lanes, the middle two will remain closed until funding is available to create HOV lanes.

Officials say HOV work would take about two years and could begin as early as 2015 on the stretch of 101 between Petaluma Boulevard South and the Sonoma-Marin county line, as early as 2016 on the rest of the Narrows. Getting the money is likely to take longer. Expect bottlenecks to continue until at least 2020, Press Democrat reporter Matt Brown wrote in a recent story.

“This whole project is setting (Highway 101) up for future HOV lanes,” Jit Pandher of the Transportation Authority of Marin said in an earlier conversation. That includes acquiring right-of-ways, doing environmental impact studies, relocating utilities and reconfiguring the highway for six lanes of traffic.

When funding for the HOV lanes is available, it will be easy to add them, providing the final link between Windsor and the Golden Gate Bridge.

Click here to read an earlier report about the southern portion of the project overseen by the Transportation Authority of Marin, including the Redwood Landfill interchange, and some answers to earlier questions (read them here).

The lion’s share of Sonoma County’s early attention has gone to bridge-building. The most complicated of the projects is replacing the four-lane Petaluma River Bridge with a new structure wide enough to hold six lanes of traffic and long enough to make more room for larger boats to pass beneath.

They also are building a new interchange at Kastania Road, requiring a new four-lane bridge across 101. And existing two-lane bridges at Old Redwood Highway/North Petaluma Boulevard and the Redwood Landfill are being expanded to four lanes, requiring the construction of new two-lane bridges alongside.

The next phase will involve regrading the hill and adjusting the curve at San Antonio Road.

Only when these tasks have been completed can the highway be widened and repaved. Starting first with the largest projects under construction:

Petaluma Boulevard South Interchange / Petaluma River Bridge ($127 million) – In addition to replacing the bridge, the existing Petaluma Boulevard South interchange will be replaced by a new tight diamond interchange at Kastania Road. The existing Boulevard will continue south on both sides of the highway, serving local traffic as frontage roads with Class II bike lanes. Once all the phases of the widening project are complete, the bike lanes will connect to those running north from Novato. (See map below.)

By doing this work to restrict vehicles from entering 101 except at formal interchanges, the highway will qualify as an expressway, setting the stage for future HOV lanes. Work began in January 2013 and should be done by 2016

Middle section of the Marin Sonoma Narrows project showing the new Petaluma Boulevard South interchange. Click to enlarge. (Caltrans illustration)

* Kastania Road interchange (included in the Petaluma Boulevard budget) — The new bridge crosses 101 just south of the existing South Petaluma Boulevard interchange. Westbound traffic will connect with the existing Kastania Road, which will serve as a frontage road serving farms and the gas station. That road will end at Gunn Road. (See map below.)  Work is underway and is expected to finish in 2015.

Just south of Gunn Road, the freeway will be shifted slightly to the west to provide a better line of sight for northbound drivers. The southbound lane will move to the west, and the northbound lane will move into the existing southbound lane. The new lanes are visible as green lines on the map below.

Marin Sonoma Narrows project south of the new interchange at Kastania Road. (Caltrans illustration)

* San Antonio curve correction (not yet under contract) — Highway 101′s alignment as it crosses San Antonio Hill haven’t changed since the road was designed in 1953 or 1954, although speeds have changed dramatically. To make it safer, the road will be moved to the west and the grade will be flattened between San Antonio Road and the Petaluma River Bridge. A new six-lane bridge also will be built over San Antonio Creek to resolve flooding issues, and a new Class I bike lane will be built along the creek, connecting east and west frontage roads.

Access to the freeway from San Antonio Road also will be restricted, with local traffic directed south along the frontage roads to an expanded interchange at the Redwood Landfill. Work is expected to begin in 2015 and end in 2017.

* Redwood Landfill interchange — Marin County has been in charge of expanding the existing two-lane bridge to four lanes and creating a true tight-diamond interchange with on- and off-ramps in each direction. It is expected to be done in 2014.

Other smaller projects further north include:

Old Redwood Highway/North Petaluma Boulevard ($27 million) – The two-lane overcrossing will be widened to four lanes, and new on- and off-ramps will be built. The new structure that will hold the two new lanes is being built alongside the existing bridge. Sound walls also are being built there. It is expected to be done in 2015.

* Lakeville Highway (Route 116) Interchange ($32.9 million) — The existing Lakeville Highway bridges will be widened to make room for the future HOV lane, and truck climbing lanes on Highway 101 will be upgraded in both directions. Sound walls also will be installed. All traffic is scheduled to shift onto the southbound bridge in mid-December so the northbound bridge can be demolished. All work is expected to wrap up in 2015.

Lakeville Highway interchange. (Caltrans illustration)

Stay tuned this week for answers to more specific questions from Road Warrior readers.



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  1. Wilson

    Questions for CalTrans

    You have known for many years this was going to happen. Why didn’t you purchase the old quarry site when it was available to make the new interchange less convoluted than it is going to be?

    Actually the Sonoma County Open Space District should have purchased the land for greenbelt separator but they haven’t really been concerned about buying important land like this until recently.

    Also. I thought that the whole idea was for eventually three lanes each direction as far south as Highway 37 in Novato. Yet the center divider all of the way through Novato has now been filled in for a fourth lane. So if ever the Narrows gets its third lane, there will STILL be a bottleneck at the north end of Novato. CalTrans, please explain that for me.

    Thank you.

    December 3rd, 2013 9:30 pm

  2. stuck in the narrows

    Why can’t we double the number of workers on all these projects? The traffic is unbearable,and is costing the County .
    When will the whole thing be 100% done? three clean lanes from Atherton Ave. -Petaluma Blvd North exit.

    December 4th, 2013 9:49 am

  3. Stephen Landwehr

    And are we going to raise the roadbed so it will not flood again at San Antonio Creek?????????
    Current residents may have never seen that.

    December 4th, 2013 3:21 pm

  4. Doug

    Wilson, I agree. I guess each county gets funding and projects approved independently, but the $50 million or whatever amount spent on widening the section of middle and north Novato to four lanes was a section that did not need widening and was a waste in my opinion. Too bad that money couldn’t have been put toward a third lane all the way. What gets me is that our transportation officials “made a choice to do the safety improvements first”. Did they consider how unsafe the main roadway would be because emergency vehicles can’t get through jammed traffic? But the dairy farmer, his 75 cows, and the 14 people that visit Olompali each year will have great improved access while the thousands of us passing through every day are forced into a tunnelway, getting jammed closer and closer between ever narrowing barriers in hour long stop and go. I’ve seen highways in the bay area widened and then widened again over the past 20 years, but now it will be another seven years for the narrows to just get a third lane? Maybe there’s not enough outcry from the north county to get this done.

    December 4th, 2013 3:43 pm

  5. Road.Warrior

    Yes, you’re absolutely right.

    December 4th, 2013 6:10 pm

  6. Sebastopol Queen

    Road Warrior, thank you for helping us try to make sense of this mess as it is maddening. There are many people to blame for our current situation, but we can all do something to make it better in the meantime.

    Fellow Commuters: will you please TAKE THE BUS??!!!
    I take the bus every day from Rohnert Park and would never even consider driving. The bus is like BEING AT A SPA compared to driving. The bus is the fastest, most comfortable, easiest, safest, least stressful and ONLY way to commute to the city, in my opinion. There are plenty of seats, everyone is silent, & no one talks to each other! I get through my work & personal emails on my phone, I make lists & get organized, and I work on files saved to my laptop. And a lot of people get GREAT SLEEP on the bus- I am not one of them, but you could be!

    If you take the bus a couple of times & get into your routine, you will never want to drive again. And I swear I don’t work for Golden Gate Transit! Please figure out how to take the bus at least one day a week. If you do, we may regain some collective sanity.
    Thank you for your help.

    December 4th, 2013 7:33 pm

  7. I'll be home in an hour, er make that two.

    The planning of this construction is terrible and slow. I have more hope that the Smart Train will be available before this third lane! Okay, who am I fooling. I have no confidence in either! Other states have much more efficient short and long term planning for their roadways than California does. Think of the lack of productivity/family time we are missing out on as a state, county or community? Ridiculous.

    December 5th, 2013 12:18 am

  8. GG

    This is ridiculous. How do these officials respond to the very justified critiques about how this project was handled? The traffic between Novato and Petaluma has been terrible for decades. I would guess that it is (and was when this project started) the worst bottleneck on Hwy 101 north of Novato. So why is this the last, least-funded portion to be started? Was the third lane between Santa Rosa and Windsor, for example, so vital that they could ignore the much, much, much larger problem at the southern end?

    This is really infuriating. Telling us that we will be waiting another SEVEN years for something that really should have been done 20 years ago is asinine. Someone needs to answer for this. More importantly, someone needs to figure out a way to get this done before 2020. If CalTrans officials can figure out a way to demolish, rebuild, test and reopen a significantly damaged and complicated portion of the MacArthur Maze in 26 days, they can figure out how to add two lanes to 16 miles of highway in less than seven years.

    December 5th, 2013 2:20 am

  9. Kevin

    We have to go through all this construction hassle for years only to end up with our original 2 lanes of usable roadway. The HOV lanes are lightly used while the other 2 are stop and go. Seems like opening up all 3 would actually be a benefit to everyone as traffic would then flow. HOV lanes presume that people are commuting to common areas, but there are no large industries that people are commuting to, so everyone has a separate destination.

    December 5th, 2013 6:47 am

  10. stuck in the narrows

    Why in the world is your overwhelming logic , which everyone who travels the narrows daily agrees with, being ignored by the authorities? The narrows are beyond un-safe(accidents daily), and it blows my mind that a new approach isn’t being taken. For example: the instant they widening 101 up to Atheron to 4 lanes, they should have brought all the workers to the Atherton area to widen to three lanes to the dump. Instead we got a WORSE chokepoint than the one that existed previously. Whenever I tell people I live in Petaluma, the first response is “oh my god, how do you deal with the traffic”…not exactly what I expected when I moved to the green acres.

    December 5th, 2013 7:46 am

  11. Cathy

    I agree with the fact that once you get used to the bus, you would rather take poison than drive in to SF under any circumstances! Why don’t people take the time to understand what they are voting for? Why are people surprised when these half-baked ballot measures end up being reality? What about the Casino in Rohnert Park? No one looked at the ramifications of the project and JUST ONE of the ramifications was the increased traffic on a 1950′s style road – 101 through the Narrows, which we will be stuck with until 2020 and when it is finally installed, wanna bet it is out of date by then? Some of the NEW BRIDGES ALREADY look too small.

    December 5th, 2013 2:49 pm

  12. Sarah

    Dear Road Warrior,

    1. How do we get more people to ride the bus to stop some of the bleeding (literally) now?

    2. From Matt Brown’s article: “But even after all the improvements, the worst bottleneck in the area will remain: the freeway will still narrow from four lanes in Marin County down to two lanes from north of Novato to Petaluma. A lack of funding will leave that 10-mile gap in carpool lanes for at least seven more years, transportation officials say”

    What can we do to change the above prediction of 7 more years of this nightmare???? Who do we need to call/ write to/picket/get out of office/fire? We want NAMES of whoever is incapable of getting the proper funding to finalize the project?

    To Cathy’s point, the Graton Casino needs to fork over a lot more than $2 mill over 10 years since we are still short $125 mill to make the widening in the Narrows a reality? Now that we have seen that the impact to the traffic is even worse than expected, what can we do to get them to write a huge check ASAP?

    Can we start preparing for next year’s election now? Can we get a “roadmap” (pun intended) for who we need to vote out & vote for & what measures to support or not from the Press Democrat & the Road Warrior?

    It is starting to feel like we live in the East Bay and we are better than that.

    December 5th, 2013 8:26 pm

  13. Monster Joe

    I agree with Kevin, recent studies (based on 15 year old data) showed very very few cars use HOV lanes. Doing away with them would be cheap and alleviate a great deal of congestion at those peak hours. Who is responsible for this decision?

    December 6th, 2013 1:23 am

  14. Stargazer

    Is there the slightest chance that our US Senator Barbara Boxer could put the weight of her office behind this project?

    For the life of me, I can’t see that she is doing anything else for her constituents. This would be a worthy project for the entire North Bay Area.

    December 6th, 2013 6:38 am

  15. ann

    As a commuter between Petaluma and San rafael with young kids, I don’t have the option of taking the bus because it is so unreliable and infrequent. I have to be able get my kids to/from school according to that schedule and do my best to acutally be at work when i am supposed to be! With a bus running once per hour and frequently late, that is simply not possible. If you want people out of their cars, you have to have at least 2 busses scheduled per hour. And the SMART train that will use only one track going south in am and north in pm??? how reliable will that be if/when there is any kind of problem on the track – or you work slightly off hours – or – or – or…….

    December 11th, 2013 2:11 pm

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