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).