Daily Archives: January 15, 2015

Is Westside Traffic Really Getting Worse?

Recently, the LA Times has published some articles positing that as freeway traffic gets worse, people have started using smart phone apps like Waze to try to avoid it, causing worsening congestion on neighborhood streets. The problem is that you can’t trust people’s perceptions of traffic. Traffic, like behavior of teenagers, is almost always perceived to be getting worse, data be damned.

Since Caltrans publishes freeway traffic counts going back to 2002, we can take a look at the evolution of Westside freeway traffic leading up to the last economic peak, the crash, and the current period of growth. Here’s a plot of traffic on the 10 between Lincoln and Vermont, from 2002 to 2013.

How to read: traffic volume is the vertical component. Time represented on the diagonal from top left to bottom right. The location on the freeway is represented west to east on the diagonal from bottom left to top right. So, if you follow a diagonal line from bottom left to top right, you’re seeing traffic volume on the freeway build as you head towards downtown. If you follow a diagonal line from top left to bottom right, you’re seeing how traffic has changed over time at a particular point on the freeway.

For example, following the diagonal for 2013, we can see that traffic is below 250,000 vehicles per day from Overland west, and above 250,000 vehicles per day from National east (where the line leaves the green area and enters the yellow band). Following the diagonal for Vermont, we can see that traffic volumes were above 325,000 at Vermont from 2002 to 2006, then between 300,000 and 325,000 from 2007 to 2011, and then back above 325,000 from 2012 to 2013.

If these graphics don’t make sense, there are some simpler line graphs at the bottom of the post showing the same freeways for years 2002, 2007, and 2013.


What can we see? Traffic declined across the whole freeway from Santa Monica to downtown LA as a result of the recession. West of La Brea, traffic volumes have not recovered or have declined even further, though east of there, traffic has started to recover. No boom in traffic on the Westside on the 10.

Here’s the 405 between the 90 and Mulholland (Sepulveda Pass). Information is the same, but the rotation is a little different to better show different patterns. I left the interchange with the 10 off the plot because it made a large, confusing dip between Olympic and Santa Monica.


From Wilshire to Sepulveda Pass, traffic volumes on the 405 haven’t increased noticeably either. There has, however, been a large increase in traffic between the 90 and Santa Monica since 2007. This correlates to both the economic recovery and the project that widened the freeway between the 90 and the 10 (induced/latent demand is real!).

Since some Westside arterials are still Caltrans-numbered routes (Lincoln, Santa Monica, and Venice) we can also look at trends on those facilities. Here’s Lincoln from the 90 to the 10.


From the 90 to Washington, traffic volumes fell in the recession and have not yet recovered to previous peaks. The stunning thing here is the drop of 10,000+ vehicles per day between Venice and the 10 freeway. It seems possible that the completion of the widening project on the 405 shifted some traffic from Lincoln to the freeway.

Further evidence for that conjecture comes from Venice between Lincoln and La Cienega.


Roughly coinciding with completion of the freeway project, Venice saw a considerable increase in traffic in the vicinity of the freeway and points east.

Lastly, here’s Santa Monica.


Nothing really jumps out here. Traffic declined during the recession, and consistent with national experience, has not recovered to previous peaks.

There’s no clear pattern of increasing traffic on these roads, but that doesn’t necessarily mean the story about worsening traffic on side streets is wrong. Technology like Google Maps and Waze makes information about the road network more accessible, and it’s certainly possible freeway and arterial traffic growth has been muted by people using the side streets. The city’s traffic data is also available through the Navigate LA website; maybe some enterprising person with programming skills can figure out a way to pull it out! Either way, it’s apparent there have been some shifts in traffic patterns, which we’d expect to make congestion worse in some places.

Note: 2009 data was missing, so I made it the average of 2008 and 2010.

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