Cars use up too much damn space

A common misconception I face is that I don’t like cars. On the contrary, cars are a wonderful thing: they give us freedom of movement, allowing us to go where we want, when we want. They are mobile rooms, so we can keep our stuff relatively safe wherever we go. They are personal mobility tools for people who have trouble walking. They’re a fabulous invention. But they use up too much damn space for everyone to use them.

Image by the author.

Or, if you prefer, a diagram of the same, with each box sized according to the space used by a traveller in the mode:

The tiny boxes in the corner are, in descending size, bus (half full), bus (full), train.

[The data above assumes a Level of Service of D for pedestrians [1], bicycles [2], and cars [3]; 1.2 passengers average for cars; 1 passenger for other private modes; 66-passenger bus; and 2,000 riders on a 10-car subway train.* Bike parking assumes 2 spaces, the size of which were estimated from a 12,500-space bike parking garage in Utrecht [4]; car and motorcycle parking assumes 3 spaces, the size of which were estimated from planning documents [5a; 5b]; and bus parking assumes a typical maintenance and storage facility [6]. Road space assumes 11-foot-wide urban lanes and 12-foot-wide freeway lanes.]

Jarrett Walker calls is this a problem of geometry: a dense city cannot run on cars [7]. There just isn’t enough space for most people to use it as their primary mode of transportation. Buses, trains, bicycles, and walking all use less space, so they become primary. I’d argue this is not just a problem of dense cities but also of chokepoints within less-dense places.

The first thing I notice is how much parking is needed, especially for driverless and urban cars. It looks like over half the space needs for urban cars come from parking, and almost three-quarters of the driverless urban car needs are from parking.

The goal of transportation planners ought to be to maximize the usefulness of their space. Driverless cars will help cut down on road usage, but their parking needs will still eat up much of the landscape. Driverless taxis would help more, but to be as space-efficient as a half-full bus they would need an average load of 20 people, and at that point it’s more bus than taxi.

In comparison, a bicyclist uses just 7 percent the space of a driver in a city. Someone on foot uses less than 2 percent.

In practical terms, the various space-intensive modes travel should be the most rare ways of getting around, used for practical reasons by people with mobility issues, people who have unusually long or circuitous commutes, and people who have loads to move. Travel by other modes should be much more common, especially at times when a lot of people want to go to a relatively compact area of the region (like at rush hour). These other modes should be just as fast or faster than driving (accomplished by improving those other modes), and relying on them should not feel like a burden.

Far from making driving harder, inverting mode shares so driving becomes more rare would actually make driving easier and better by making other modes much easier and much better. There’s no reason to give away 2,300 square feet of space to every car traveler when 27 square feet by bus or 7 and a half feet by train would do just fine for most trips.


* Trains are the only vehicle here that must operate in their own right-of-way. They can move around 50,000 people per direction per hour using realistic headways compared with 4,800 on buses in their own right-of-way. Without stops, which would approximate the other modes' metrics, a train could operate about twice as often and yield the 7.5 square feet needed per passenger indicated here. A parallel article would examine lane capacity, but that would necessarily exclude parking - a key factor in cars' inefficiency - and so this is not the place for that examination.

Works Cited

[1] “Current HCM Methodology,” in Pedestrian Level of Service Study, Phase I (New York, NY: New York City DCP, 2006).

[2] Dan Zhou et al., “Estimating Capacity of Bicycle Path on Urban Roads in Hangzhou, China” (Conference Paper, The 94th Annual Meeting of the Transportation Research Board, Washington, DC, 2015).

[3] Energy Facility Site Evaluation Council, “Appendix C: Transportation,” in Kittitas Valley Wind Power Project Draft Environmental Impact Statement (Olympia, Washington: Sate of Washington, 2004).

[4] Juliana Neira, “World’s Largest Bike Parking Garage Opens in The Netherlands,” Designboom, August 10, 2017.

[5a] “Design and Improvement of Parking.,” Section 19.26.040, Roseville Municipal Code, accessed August 18, 2017; [5b] Peter Croft, “Light Vehicle Sizes and Dimensions: Street Survey Results and Parking Space Requirements – Information” (Auckland, New Zealand: Land Transport NZ, December 2004).

[6] Division of School Support, “School Bus Maintenance Facility Planner” (Raleigh, NC: North Carolina Department of Public Instruction, February 2011).

[7] Jarrett Walker, “Does Elon Musk Understand Urban Geometry?,” Human Transit, July 21, 2016.

Let’s get into the weeds: a congestion charge plan for Marin

Last week, we discussed how tolling designed to eliminate congestion would improve travel times and improve the efficiency of our roads. [1] This week, we get a bit into the weeds about how such a plan would work.

How to eliminate congestion in the North Bay

Marin has four main entrances, three of which have significant rush-hour congestion: the Novato Narrows, Highway 37, the Richmond-San Rafael Bridge (RSRB), and the Golden Gate Bridge (GGB), with Highway 37 being the odd one out of the congestion game.* These congested gateways are a drain on people’s time and public resources. The Narrows is only moving 85 percent of the vehicles per hour that it could, the RSRB moves just 61 percent, and the GGB moves just 74 percent capacity.**

The entrances are all chokepoints, with few or no parallel routes, so they are ideal for tolling. The toll need to be charged both directions, so existing tolls on the GGB and RSRB would be cut in half: half heading inbound and half outbound.

A toll that eliminates congestion would allow another 4,380 vehicles per hour to move at rush hour, a staggering 35 percent increase over today's numbers.

To determine the exact amount a congestion toll ought to be, we need some pieces of information: the maximum number of vehicles per hour each road can move, also known as their flow rate; the existing flow at peak hour; the amount of demand there is at peak hours; how long the flow is congested; the length of the congestion; and the median income of the area. If all of this is known, then a little calculus is needed and then, voilà, the result. Unfortunately, with publicly available data it is very difficult to determine demand, so we need to work a little bit harder for a less precise number.

I wanted to find out how much extra time people were spending in traffic than they would if all the roads were at their maximum flow and how much that lost time is worth. Tie these elements together and we get some estimates. The Narrows needs a charge of about $5 ($108 extra per month), the RSRB needs $5 on top of its existing toll (, and the GGB needs $6 on top of its existing toll. Combined, these tolls would bring in an additional $102.4 million per year, which could be used to secure bonds of up to $1.3 billion (over 30 years at a 4 percent interest rate). For context, the Golden Gate Bridge brought in $129.5 million in toll revenue in the 2015/2016 fiscal year. [2]

Look regional

Because Marin’s transit system is part of a broader regional system of bridges and highways, any tolling plan would need to be regional in order to ensure that traffic doesn’t spill over onto some other road. As previously mentioned, Marin’s entrances have very few good roads and therefore can be fairly easily tolled. However, if Marin manages to unclog its traffic, East Bay commuters might try to cut through the county on their way to San Francisco. More drivers on Marin’s roads means higher tolls, and then Marinites and Sonomans would have to pay more than before. Any toll plan would need to be implemented across the whole region to ensure all the region’s freeways are used as efficiently as possible and nobody is charged too much.

Build equity into the toll

One of the oft-cited problems with charges like this is that it is regressive as it hurts the poor, who have more time than money, more than the rich, who have more money than time. I outlined a solution briefly last time, [3] but here it is worth fleshing out a bit more.

Carbon taxes are often structured in such a way so as to be revenue neutral, [4] so whatever income is generated is refunded to the users. However, an unclog-the-roads toll, like what’s proposed here, should be used to increase the tolled travel corridor’s capacity and so needs to provide a useful income. This could be done either by selectively exempting vehicles registered to poor drivers, but that would be logistically difficult. Instead, tolls should be a refundable state tax credit that phases out as income increases. (Refundable tax credits are refunded to the taxpayer whether or not she owes any money, and so they are always returned.) FasTrak, or whoever the vendor is, would inform their registered users every year how much they paid in congestion tolls, which the users could report on their taxes. Non-registered users, like tourists or infrequent users, would not get a form so they’d end up paying no matter their income.

It’s difficult to estimate how much of the toll income would be refunded, but given that drivers tend to be wealthier in general, especially in the suburbs, this may not be a significant portion of toll revenue. Should it become viable to issue monthly rather than annual refunds to poor drivers, it would likely encourage driving, which would in turn increase congestion. That would require higher tolls, offsetting the revenue lost to refunds.

Regardless, because the toll essentially is trading time for money, and the amount of time currently used up in traffic is worth about $102 million per year, that is roughly how much would come in from these tolls.

Next time, we will consider just what might be done with this revenue stream to make travelers lives better.


* Traffic from 37 does add to congestion on Highway 101 to the south, and congestion does regularly crop up on the road, but the MTC analysis this post relies on [5] reports very little congestion on the road itself. Without a proper traffic management analysis, it would be tough to say how these tolls would actually shift congestion around the North Bay.

** This is current peak-hour flow divided by optimal traffic flow. Optimal traffic flow is the maximum capacity of highway lanes [6]; peak-hour flow is from Caltrans [7].

Works Cited

[1] David Edmondson, “The Science of Traffic and Its Awfulness,” The Greater Marin, July 3, 2017.

[2] Golden Gate Bridge, Highway, and Transportation District, “Comprehensive Annual Financial Report,” Annual Report (San Francisco, CA: Golden Gate Bridge, Highway and Transportation District, 2016).

[3] Edmondson, “The Science of Traffic and Its Awfulness.”

[4] UNFCCC, “Revenue-Neutral Carbon Tax,” Momentum for Change, accessed July 4, 2017.

[5] Metropolitan Transportation Commission, “Time Spent in Congestion,” Vital Signs, accessed April 29, 2017.

[6] John D. Zegeer et al., “Default Values for Highway Capacity and Level of Service Analyses,” National Cooperative Highway Research Program (Washington, DC: Transportation Research Board, 2008).

[7] Division of Traffic Operations, “2015 Traffic Volumes on California State Highways” (Sacramento, CA: Caltrans, 2015).

The science of traffic and its awfulness

If only the guy in front of you would drive better, perhaps you wouldn’t be stuck in traffic. Slow, fast, break. Slow, fast, break. Shift lanes. Whoever it is, that driver sucks.

That’s what the driver behind you thinks about you, and what the driver behind that driver thinks about him, and so on. It’s traffic congestion, and it’s bad for everyone.

There are two aspects of congestion to be explored here in very brief detail: its physical results and its economic causes. Only once we understand the economic causes will we be able to figure out a solution.

Traffic makes roads terrible

Roads move traffic at a rate governed by a very simple model: the density of the vehicles per mile times their speed. But there is a trade-off. As the density of vehicles goes up, their speed goes down as drivers become more cautious. There’s a balancing point where density and speed allow a road to move the most vehicles. Shift the density a bit either way, and you don’t move as many vehicles, and you’re not getting your money’s worth out of the road. The relationship looks like this:

When traffic gets bad, roads exist on right-hand side of the diagram. Drivers like being on the left-hand side where speed is pretty high,, and taxpayers should want to be right in the middle, getting the most for their money. Image from ACCESS magazine [1]

When traffic gets bad, roads exist on right-hand side of the diagram. Drivers like being on the left-hand side where speed is pretty high,, and taxpayers should want to be right in the middle, getting the most for their money. Image from ACCESS magazine [1]

So, traffic congestion is when the road is operating somewhere on the right side of the curve. Basically, at rush hour, there are too many people that want to use the road all at once, increasing density way past the efficient level, making everyone slow down and the roads awful. This video does a good job of showing how this works. It’s boring, but stick with it [2]:

Basically, everyone slows everyone else down by trying to use the road all at the same time. Every additional vehicle on the road slows everyone else down just a little bit, which adds up to a lot. Past the balancing point, each additional vehicle also makes the road less efficient. Just how much is something we can quantify.

Time is money

When someone is slowed down in traffic, they get to wherever they’re going later than they’d hoped. This might cost maybe a few minutes, but when multiplied out over everyone stuck in (and causing) that traffic it ends up being a lot of person-hours. Economists, measuring a whole host of factors [3], translate this time cost into a monetary cost. Every vehicle “pays” a certain amount of time (alongside gas, maintenance, and tolls) which is the average cost of using the road. When someone new comes into the road, that average cost goes up just a little bit at the margins. This is called marginal cost of using the road. Each driver feels only the average cost; the marginal cost is divided up evenly between everyone else around them on the road. It’s like when someone cuts in line: everyone behind them is slowed down a bit.

In short, every vehicle faces the average cost and forces everyone else to “pay” a little bit more. Brendan O’Flaherty writes:

The final major kind of external cost that drivers impose on each other is congestion. On an otherwise deserted country road, or even on most city streets at four o'clock in the morning, it's difficult for one car to get in the way of another car or to impede its progress, and so congestion is not a problem. But when tens of thousands of cars an hour are converging on the Lincoln Tunnel during rush hour, they get in each others' way, and since the number of cars that can go through the tunnel in any minute is less than the number that want to go through, each car that enters the tunnel during rush hour is forcing all the cars behind it in the queue to wait a few seconds. Because drivers don't bear the cost of the congestion they cause, they cause too much of it.
I'm not saying that drivers don't bear the costs of congestion. Of course they do; being stuck in a traffic jam is unpleasant and time-consuming. But I don't bear the costs of the congestion I cause; instead I bear the costs of the congestion you cause, and so you have no incentive not to cause it. Or more starkly, think about a line of cars going through the Lincoln Tunnel. The first car may encounter no congestion, but if it were vaporized, every other car would get through the tunnel more quickly; and so the first car is causing a lot of congestion. The last car, by contrast, is encountering a lot of congestion, but causing none (if it were vaporized no one else would get through the tunnel sooner). [4]

O’Flaherty goes on to also describe how people shift their schedule around to avoid traffic, which has its own cost, and how people sometimes just grin and bear it, choosing to drive in traffic and pay that cost on the road instead. [5]

But all this cost is just in terms of time. It’s wasted, lost to everyone. If there were a way to shift that cost into dollars, then it would be possible to put that cost to productive use, or to return it to the people who need money more than time.

Anti-congestion toll

This is where congestion pricing, or demand pricing, or surge pricing, or whatever you want to call it, comes in. In essence, it’s a toll that charges people what they would otherwise pay in terms of time as well as the cost they impose on other users of the road (the marginal cost). This smooths out demand, so the road never gets clogged, and allows the money to be put to better use. The tolls collected could also be returned to poor drivers as a refundable tax credit. (I would have the electronic toll collector contractor, i.e. FasTrak, mail out a tax form to each of its customers itemizing the amount paid in anti-congestion tolls by month, which the customer could report on their taxes as a credit contingent upon income.)

The goal would not be to return the road to free-flow speed, but rather to the balancing point, where a road moves the most cars per hour possible. More people would therefore be able to get through the system at rush hour, meaning the whole driving system would be more efficient. Any money not returned as a tax credit could sponsor public transit or road improvements.

The London tolling plan, which did not include the tax credit, saw travel times fall and then stabilize within the controlled area, though traffic volumes continued to fall significantly. [6] London also saw the number of crashes and traffic deaths fall significantly. [7] The Stockholm plan saw the similar results but, intriguingly, drivers who were interviewed after the toll went into effect didn’t think they had changed their travel behavior. [8]

This is the only way to ensure congestion doesn’t occur without a recession because, as discussed above, people normally don’t feel the cost they impose on everyone else on the road and so they overuse it. With a toll like this, people will feel the full cost of their road use and so allow society to get the most out of the investment in roads.

Of course, people don’t like to be charged for what they previously got for free, especially when that would represent an unknown change. Stockholm residents, for instance, hated the idea of a congestion charge until it was attempted. [9] Manhattan has tried for years to implement a charge only to be blocked by state lawmakers. [10] When San Francisco talked about doing something on the Golden Gate Bridge, then-San Rafael mayor Al Boro called it a “Marin commuter tax.” [11]

Nevertheless, given that it is the only way to permanently resolve traffic, it is worth exploring how big the charge would be and what is possible with that income. That’s what we will explore next time.

Works Cited

[1] Richard Arnott, “A Bathtub Model of Downtown Traffic Congestion,” ACCESS Magazine, June 1, 2015.

[2] Washington State Department of Transportation, Doug MacDonald - Rice and Traffic Congestion, 2007.

[3] J. Hewitt, “The Calculation of Congestion Taxes on Roads,” Economica 31, no. 121 (1964): 72–81, doi:10.2307/2550927; Roberto Ayala, “The Value of Travel Time Savings: Departmental Guidance for Conducting Economic Evaluations Revision 2 (2014 Update)” (Washington, DC: US Department of Transportation, July 9, 2014).

[4] Brendan O’Flaherty, “Congestion,” in City Economics, 1st ed (Cambridge, Mass: Harvard University Press, 2005), 52.

[5] Ibid., 56.

[6] Transport for London, “Public and Stakeholder Consultation on a Variation Order to Modify the Congestion Charging Scheme Impact Assessment” (London, UK, January 2014).

[7] Alex Davies, “London’s Congestion Pricing Plan Is Saving Lives,” Website Type, Wired, (March 10, 2015).

[8] Jonas Eliasson, How to Solve Traffic Jams (Lausanne, Switzerland: TEDxHelvetia, 2012).

[9] Ibid.

[10] Ben Fried, “Factchecking Cuomo’s Revisionist History of NYC Road Pricing,” Streetsblog New York City, February 18, 2015.

[11] Michael Cabanatuan, “Bridge Raises Tolls, Denies Doyle Dr. Funds,” SFGate, March 15, 2008.

Anti-urban groups fight to keep Drake congested

MAD: Fighting to make its logo a reality. Image from MAD. [1]

Despite years of arguing new housing will exacerbate traffic congestion and blaming the county’s urbanists for indifference to the problem of congestion, Marin Against Density (MAD) is now fighting against new traffic lanes on Sir Francis Drake (Drake), arguing the project will actually reduce capacity. Fact check: it won’t.

The project

Drake Boulevard is a mess south of Ross from every perspective. To people on foot or bike, it’s a hot, loud, dangerous traffic sewer. To people in cars, it’s a congested nightmare every rush hour. Thankfully, there’s enough space on the road to make the first problem a little less bad and fix the second problem.*

The biggest change to Drake would be a third lane heading south from Marin Catholic to 101 and, in one design, north from 101 to El Portal by narrowing lanes from between 15 and 21 feet to a standard 11 feet. This will increase capacity by about 50 percent along the most congestion stretches of the road, a huge boost for drivers that have complained about for years.

Other changes would be squaring off intersections in a few sections to make it safer to walk, new shoulders – formerly Class II bike lanes – and wider sidewalks [2]. Given that there are schools along the route, these are victories for parents and children along the way.

So what’s the problem?

According to an email from MAD [3], and to comments from anti-urbanists from the last time I tackled this problem in November [4], the primary complaint is that narrowing lanes will reduce capacity by slowing traffic. They’ve labelled it a traffic calming exercise, designed to support safety rather than traffic flow.

Even if we look past the morally reprehensible attitude that the safety of people walking isn’t worth protecting, it’s utterly illogical. MAD doesn’t understand how roads work.

A short primer on road capacity functions is in the notes, if you’re interested, but here’s the short of it: moving from a 12-foot lane to an 11-foot lane will decrease the free-flow speed of a road by about 3 percent, but adding a whole new lane will increase capacity much more than what’s lost by that very slight depression in free-flow speed. Add it all up, and the project should boost capacity by 45.5 percent.

But what about right-turn lanes lost? There is still more road capacity, so while the far right lanes might be slower during off-peak times, through drivers who won’t be in the far right lanes won’t need to worry.

To put it very simply, the county wants to slow uncongested travelers by about 3 percent to add 50 percent capacity. This seems like the kind of project MAD would support if it was so worried about traffic.

But MAD’s opposition to adding makes so little sense it boggles the mind. Why would an organization that argued any new homes will cause congestion fight against measures that might actually reduce congestion? The political answer might be the easiest.

It’s an election season, and that Fairfax email was rife with disparaging words for incumbent supervisor Katie Rice and glowing words for the conservative, Kevin Haroff, who has come out against the project [5]. By painting this redesign as a road diet rather than the road widening it is, MAD and its fellow organizations (CVP and Citizen Marin) can say that Rice has no solutions and is beholden to the madness of us urbanists.

If it’s about politics, then MAD is lying about the project to help their candidate and Haroff is complicit in the deception.

Of course, lots of anti-urbanists see a conspiracy to destroy Marin’s character. They probably actually believe that adding bike lanes is just part of that conspiracy. Al Dugan thinks I work for an anti-Marin lobbying group in DC, for instance.

So some people are playing the political game and don’t care if they’re on the technically correct side of a given issue or not as long as their candidate wins. Others want their candidate to win because they think only by cleaning house can they halt the spread of dangerous ideas in Marin. It’s a potent mix, and it‘s leading Marin down a dark path.

If even a project that will boost traffic capacity by nearly 50 percent is successfully painted as a congestion-causing project, there’s something seriously wrong with our politics. When we can’t even agree on what’s real or not, we cannot have a successful government. Fairfax went through this during Frank Egger’s years on the council. San Anselmo is going through its own turmoil with Ford Greene. Sausalito and Marinwood are going through phases when the whole governing body is dominated by people who take this sort of confrontational and personal approach to governing.

The Drake project has its problems, and I’ve highlighted them before, but as a symbol of our political dysfunction it is extremely worrying.


* For today, I’m not going to get into induced demand and the Fundamental Law of Traffic Congestion, which Connor Jones went over this past winter [6]. That’s a deeper problem, but fixing it is something nobody has the political stomach to take on even in San Francisco, let alone Marin.

Level of Service diagram, click to enlarge. Image from Wali Mamon.

** Traffic capacity – how many vehicles a road can carry in an hour – is a function of a road’s design speed and the road’s traffic jam density, or how many vehicles fit per mile when traffic speeds are basically zero:

Maximum Capacity = Number of Lanes × ((Free-flow Speed×Jam Density)/4)

This is called the Greenshields model, which is a reasonable tool for analyzing roads like this. Among other things, it tells us that as speed decreases, the number of cars the road can move per hour actually increases, at least up to a point. This is thanks to the fact that the space between cars decreases as speed decreases, allowing the road to be used more efficiently. Generally speaking, this is around Level of Service (LOS) grade E, though engineers try to keep LOS at around C or D to ensure some slack in the system [7].

According to this model, reducing the free-flow speed by 3 percent in this model to add a new lane will increase the maximum capacity by roughly 45.5 percent.

Works Cited

[1] Marin Against Density, MAD Logo, Digital Image, n.d.

[2] Kentfield Planning Advisory Board, “Sir Francis Drake Boulevard Corridor Rehabilitation” (Kentfield, CA, October 28, 2015).

[3] Marin Against Density, “Attend June 1 ‘Open House’ -- Forward This to Friends.,” June 1, 2016.

[4] David Edmondson, “Build Something Better on South Sir Francis Drake,” The Greater Marin, November 18, 2015.

[5] Issues,” Kevin Haroff for Supervisor District 2, accessed June 2, 2016.

[6] Connor Jones, “The Street Economics of Induced Demand,The Greater Marin, December 21, 2015; Connor Jones, “The Four Biggest Myths about Induced Demand,” The Greater Marin, January 4, 2016.

[7] Francis Vanek et al., Sustainable Transportation Systems Engineering: Evaluation & Implementation (New York: McGraw-Hill Education, 2014), chap. 7; Wali Memon, “Highway Level of Service,” October 12, 2012.

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.