Post #398: Per VDOT, traffic isn’t getting worse in Vienna, or on I-66, …

Posted on September 27, 2019

This post is more-or-less a continuation of Post #396, traffic trend on Courthouse.  I had to download all the VDOT traffic counts to do that, so I figured I might as well package those numbers up in some form that people could access easily.

What I found when I did that is that, per VDOT, traffic counts are stable-to-declining throughout Vienna.  So it’s not just Courthouse where VDOT shows no increase in vehicle counts.  It’s pretty much all of Vienna … including I-66.


The data file below is an Excel workbook (.xls) summarizing 2006 – 2018 Town of Vienna traffic counts on the VDOT website.

VDOT traffic counts 9-27-2019

Here are a few things to note.

  • VDOT only routinely measures traffic on a handful of Vienna streets.  Various other entities (the Town, or developers) will do ad-hoc counts on other streets.
  • VDOT has detailed data for a few years prior to 2005, but that’s only publicly available as .pdf files.  If you have a particular interest in a particular road, for 2001 – 2004, you can look that up on the VDOT website.
  • VDOT shows a traffic count for every year, but it only actually measures traffic roughly once every three years.  In between measurements, it extrapolates based on an assumed rate of growth.  The workbook above only shows the years in which VDOT made an actual traffic measurement on a street.
  • VDOT typically measures traffic for just a few days, so there will be some random variation from year to year based on exact traffic conditions during those two days.

My main takeway is that there has been no strong upward trend in cars on the road more-or-less anywhere in Vienna.  Or, at least, that’s what VDOT says.  This assumes that VDOTs methods are consistent across years.

Here are two ways to see that, both telling the same story.  The first is a count of “vehicle miles traveled” in Vienna, excluding I-66, per VDOT.  This is a VDOT estimate of all the miles, that all vehicles combined, traveled on Vienna streets in any one year.  The second is a simpler way to get at an aggregate, totaling the vehicle counts across the 24 street segments in Vienna that were reported consistently over the entire period.  Either way you do it, there’s no trend to speak of.  Both of these graphs exclude I-66.