What's the Traffic Impact of Larkspur's 920 Units?

Transit advocates maintain that many of the new residents of the 920 units envisioned for Larkspur Landing will take transit. This merits some scrutiny. I'm no traffic engineer but I wanted to at least build a cursory understanding of the facts.

For perspective today highway 101 at Larkspur carries 13,300 vehicles per hour in the weekday evening peak - and we all know how horrendous that is (Source: Caltrans 2012 traffic volumes, page 142).  

What Traffic Impact Might 920 Units Have?

According to the Institute of Transportation Engineers trip generation manual one should plan for each housing unit generating 6.715 trips each weekday. This manual is the gospel of traffic planning. Based on this factor 920 units at Larkspur will generate an additional 6,177 weekday trips. However, this figure is under-representative as the additional shopping and hotel will significantly add to this figure. 

Transit oriented development is the brainchild of Robert Cervero. In 2008 Cervero published a study entitled Vehicle Trip Reduction Impact of Transit-Oriented Housing. In his study he reviews 16 transit oriented development locations and arrives at the conclusion that in such locations trips are significantly reduced - to only 3.754 weekday trips per housing unit. Here the Larkspur plans would add an additional 3,453 weekday trips.

Now it must be said:
  • Cervero's lower trip number is the best case using handpicked ideal transit oriented development locations. Several of these locations are under 15 minutes from a major city on a direct bus route.
  • Not all trips will occur in the critical evening (or morning) peaks
  • Not all trips will be on 101
  • This number excludes the traffic generated by the proposed hotel and expanded retail
The question remains - what will the impact be of between 3,453 and 6,177 trips on highway 101 at Larkspur's critical choke-point which is currently beyond capacity handling an existing 13,300 cars per hour in the evening commute. We must also remember Larkspur is not the only thing adding traffic to 101:
  • Sonoma County is really embracing Plan Bay Area and transit oriented development. Sonoma has designated 12 "priority development areas" which if built out over the next 20 years will add 24,010 new housing units with residents easily exceeding that of San Rafael. This will surely have an impact on 101 in Marin.

  • While there is a Greenbrae Corridor Project which was intended to alleviate 101 traffic, the outcome is some bike and pedestrian improvements but for traffic the only progress is to ask MTC for money to conduct further investigations; it years away from shovel ready solutions.
Larkspur can impose mitigation fees on developers to alleviate (where feasible) impact on local intersections and on/off ramps, but I do not believe it can impose fees to alleviate the impact on 101 (I would welcome being corrected here).

Concentrating Housing

What is concerning is that 920 units will all be concentrated in a single location. I am an advocate for absorbing the projected housing need, based on the State Department of Finance projections, which is that the entire county will grow by 4,543 residents or 1,740 additional housing units over the next 25 years.

Envisioning 920 units in a single location - Larkspur  - that's more than half what's needed for the entire county - and placing this at the county's single biggest traffic bottleneck does not seem to be good planning.

Second Units

Instead we need to push for relaxing laws that currently discourage second units. I know that even transit advocate Dave Edmondson is with me on this. We should push for more Marinites to build second units.  We should also be pushing on ABAG to allow second unit to be counted towards meeting quotas - quotas that if not met lead to massive penalties as discovered by the cities of Menlo Park and Pleasanton.

We should encourage the owners of these second units to accept section 8 residents. This constituent group of Marin residents really needs the break and the state absorbs almost all risk of payment default to landlords. But the need for section 8 housing is getting increasingly acute as funding is cut.

Building Conversions

Second we need more building conversions.  I was thrilled to read about a recently announced proposal to convert the office atop the hill above Northgate Mall in Terra Linda being converted to 77 housing units. 

If we can get over this fixation on concentrating housing near transit we can start to spread out the impact of additional cars. Sure there will be more cars, but at least they won't all be concentrated at the Larkspur bottleneck - the very worst location in Marin where the additional traffic could be added.

The bigger issue for me is that Marin need not be ruined with more monstrous Win Cups - at least not in our lifetime. One Marin IJ commentor wrote it best - people moved to Marin to get away from concentrated urbanization, they came for the open spaces and a great suburban and rural environment to live and perhaps bring up a family.

Trips May Be Reduced, But Larkspur SAP Still Adds More Cars

What seems to be overlooked by transit advocates is that while their proposed high density locations near transit may reduce trips, when you put hundreds of housing units in a single location there is still a significant increase in trips. 

Adding 3,453 - 6,177 vehicle trips to the immediate Larkspur area where many will be on 101, when 101 is at capacity with 13,300 vehicles per hour peak weekday evening commute  is a bad recipe.

Marin is not like Los Angeles or the South Bay - we are highly dependent on a single artery - highway 101. Once that gets overly congested there's simply nowhere to go. So let's not ruin our critical artery 101, or ruin our beautiful county.

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

Walter McClellan January 07, 2014 at 10:32 AM
Richard Hall is absolutely right -- Marin doesn't need more "stack and pack" high-density monstrosities. Our quota can be met with second units that also have the potential to bring a homeowner additional income. It's easier than ever to get a second unit approved ministerially (by staff) now that State law mandates it in accordance with AB 1866, passed in 2003 as an amendment to the Housing code that promotes second units throughout California. If a proposed second unit meets the standard development code, the law requires that it be approved. See http://www.hcd.ca.gov/hpd/hpd_memo_ab1866.pdf for details on how it works.
Here since 1970 January 09, 2014 at 04:20 PM
@marinpcguy, regards the current drought surely you note the screaming silence of MMWD regarding our lack of dependable water supply vis a vis this project. New service hookups were reduced to a trickle for several years during the 70s drought. Just remember the currently-shelved MMWD project to desalinate water, which voters recently rejected. I'm sure those who were behind this plan can't wait for the chance to justify renewing this project - after the 920 units are built and water becomes even more a problem here.
Guy Meyer January 10, 2014 at 02:19 AM
It's really hard to imagine how anyone can believe this and other large scale construction projects along highway 101 have any benefit whatsoever for the citizens of this community. We have to say no and the people of California have to demand a completely fresh look at the unlimited growth concept of even our civilization. Survival is another word for sustainability. Quality of life is an issue that we need to embrace completely as an inherent right and duty of it's citizens to protect and defend. State mandated growth or even wealthy developer mandated growth is no longer acceptable.
Richard Hall January 10, 2014 at 09:18 PM
I've just learned Win Cup 2.0 is now on it's way through the Corte Madera Planning commission. 100 units.
Patti January 13, 2014 at 11:57 AM
Thank you Richard for your work on this. Let them build the freeways first. Then we can discuss more apartments. This will give us another ten years to think about the wisdom of our actions.


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