Marin’s traffic in the decline – except at peak

On Marin’s roads, driving is down, daily traffic is down, and morning commutes are worse. The odd and seemingly contradictory data helps shed light on some of the core problems of congestion and travel in our county, and helps us confirm (and dispel) some myths about the state of driving.

Introduction to the data

On state and federal roads in Marin (highways 1, 37, 101, 137, and 580), Caltrans keeps track of average daily traffic volumes over the course of a year, average daily traffic volumes in the busiest month, and peak hour traffic volumes.  The latest dataset is from 2013, and there’s no data for 2009 or 2010.

California’s Air Resources Board (ARB) keeps track of the vehicle miles travelled, or VMT, throughout the county. When combined with data such as number of vehicles and number of people, we can know how many miles the average driver puts on their vehicle.

Broad trends

The broadest trend in Marin is faster traffic growth at the peak hour than during the rest of the day. This is most pronounced in Highway 101 north of Larkspur, where peak volumes rose an average of 9 percent between 2012 and 2013 while daily volumes are essentially flat.

This strongly implies people are driving to work more, that work is further away, and that more people are commuting to Marin from other counties.

Data from the ARB and Census backs up these hypotheses. Per capita VMT and trips per day has declined substantially since 2000 even while average distance to work has climbed, both for Marin’s working population and its workforce.

Trips per capita have seen steady declines since 2007, while VMT has only perked up in the past two years since its high in 2002.

Travel distance has continued to grow,at the expense of the shortest commutes under 10 miles.

Localized trends: Tam Valley

Perhaps nobody’s traffic has received such attention than Tam Valley’s. Complaints about Muir Woods tourists clogging local roadways have become integral to the neighborhood’s politics, but Caltrans data doesn’t quite bear out this narrative.

While travel to Muir Woods grew over the past five years, it actually declined in 2012 and 2013. As well, despite the overall growth, drivers diverting to Panoramic Highway – the access road to Muir Woods – only account for about 7 percent of peak-hour traffic at Tam Junction, the main intersection. Even during peak season, just one tenth of daily travel is to Panoramic Highway. The real growth comes from Mill Valley’s rush hour.

Commuter traffic coming from Mill Valley down Almonte Boulevard grew 23 percent from 2012 to 2013, a huge jump in an area with terrific backups. This is in spite of a 6 percent decline in daily traffic volumes at Tam Junction over the same period.

If tourists were the reason for the traffic backups today, volume would need to have spiked by 20 percent in 2014 to return to the high of 2011, which was long before the current ruckus over tourist traffic began.

Localized trends: Tiburon

Traffic is way, way down on the Tiburon Peninsula’s Highway 131. Between 2001 and 2013, volumes dropped by as much as 40 percent, or an astounding 19,000 cars per day. Rush hour traffic didn’t drop quite as much, but a 9 percent fall is nothing to sneeze at.

This fall fits almost perfectly with the decline in jobs and workers on the Tiburon Peninsula. According to LODES, the number of workers commuting out of Tiburon dropped by about 10 percent between 2001 and 2011, and the number of workers commuting in dropped by about 9 percent.

Localized trends: Highways 101, 37, and I-580

Marin’s spinal Highway 101 can be broadly split in two: the area south of the 580 Junction and the area to its north. Beyond the cultural differences between Northern and Southern Marin, they have different commute sheds, with northerners more likely to commute to San Rafael, and more likely to endure traffic from Sonomans, than their southern compatriots. Between 2001 and 2013, rush hour traffic grew slower and daily traffic fell south of 580, the opposite of what was occurring north of 580.

I-580 is undergoing similar transformations, with rush hours growing much faster than daily volumes. Though travel on all modes was essentially flat between 2011 and 2013, between 2010 and 2011 the rush hours grew mightily, heavily weighted toward the 101 junction. Between the 101 junction and Sir Francis Drake rush hour volumes grew an average of 27 percent; to the east of Sir Francis Drake, rush hours grew by just 12 percent.

Part of the reason for the growth in Northern Marin – though by no means all of it – is the significant added volume on Highway 37 to Solano County. While rush hours were once comparable to Highway 1, rush hour volumes are up 17 percent, and daily travel is up by a similar amount.

The growing importance of San Rafael as a jobs hub for Sonoma and Northern Marin is likely the cause of worsening rush hours on all three roadways.

Policy implications

Given the growing importance of San Rafael as a commuter destination, it is more important than ever for that city to do what it can to reduce the demand to drive into its downtown from the north, and for Sonoma’s transit agencies to treat it with the same seriousness GGT gives to San Francisco.

The lowest-cost policy for San Rafael and for the County is to aggressively approach the problem of parking as part of a broader transportation demand management scheme. Important to that would be to eliminate parking minimums downtown, establish parking permit districts in the surrounding neighborhoods to prevent overflow, and price street parking sufficiently to ensure there’s always a space available on the block where you want to park.

The location of growth in 101 traffic speaks to the importance of SMART in alleviating traffic congestion. 101’s 14-15 percent growth in peak hour traffic (really both of the two-hour morning and evening rush hours) heading to San Rafael from the north amounts to only about 500 cars per rush hour. Given how much a difference these extra cars have made to Northern Marin commutes, diverting an equivalent number of trips to a train would be a major boon.

Highway 37 is a sticky wicket. Widening the road would simply add congestion to 101 and encourage it near Vallejo. Congestion pricing and buses would be a far cheaper and more immediate solution. The ongoing study of travel along Highway 37 should incorporate both of these.

In Southern Marin, the travel demand from Mill Valley to San Francisco has already made Route 4 one of the most productive in GGT’s system. Further boosts to transit through that corridor will pay off, especially measures to allow buses to bypass the heinous backups.

Conversion of general travel lanes on 101 south of Marin City to HOV lanes would likely pay off upstream. Encouraging people to carpool or take faster buses – and there is no such incentive for Southern Marinites today – will mean fewer vehicles at the various chokepoints like Tam Junction.

Finally, while the drop in traffic around Marin is welcome, if travel isn’t replaced by other modes it’s a worrying sign for Marin’s economy. Cities and the county must invest in their protected bicycle infrastructure. Studies in comparable locations around the country have found people arriving by bike are much better customers for downtown businesses than people arriving by car. Marin is well-primed to take advantage of that fact, with its vibrant mountain biking scene and walkable town centers.

The siren songs of wider roads and a housing moratorium

The reflex is to forego all this transit-and-biking mess and push for more roads, or to call for a moratorium on housing. Both would be foolish.

It has been known since the 1930s that more roads simply fill up with more cars. Widening 101 at the Novato Narrows is expected to displace congestion from the Sonoma/Marin border to Central San Rafael. Widening 580 will only encourage more people to swap their Bay Bridge commute for a Richmond Bridge commute.

Housing moratoria won’t work either. Rush hour traffic has grown far, far faster than population. San Rafael and Tam Valley have seen almost no housing growth in the past five years but have seen stupendous rush hour traffic growth. There needs to be a plan to reduce driving demand among Marinites. Reflexively calling for a housing moratorium is misidentifying the problem, pointing the finger outwards when Marinites themselves are the cause of the problem.

Opponents of housing have floated an innovative idea: remove parking minimums from local development codes. If properly sited and blended with local retail, this housing could actually facilitate a drop in traffic. Portland conducted a comparative study of transit-oriented and car-oriented developments and found that the number of car trips diverted was far greater than the number of new transit trips. The authors speculated this was because more people were able to walk or bike from home for their daily errands.

A housing moratorium, then, is bad medicine from a misdiagnosis of the problem. Rather, Marin needs a parking moratorium. Coupling that with the transportation alternatives listed above could prove a sea-change in how Marin gets around, and may put a halt to the rapid rise in traffic.