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.
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.
Continue reading on the new site, theGreaterMarin.org.