FHWA Changes the definition of Congestion

The Federal Highway Administration published an article today redefining congestion.

As I presented to the House Transportation Committee last year,
there are 4 ways to reduce congestion:
1. Increase capacity
2. Reduce demand
3. Improve efficiency
4. Change your definition of congestion

Their article is addressing #4.

The article also gives credit to my point that moving Vehicles per Hour (vph) is not as important as moving People per Hour (pph) On this point WSDOT claims to agree as I quoted from their blog in my presentation:


However, what is done in word is not done in deed by WSDOT.  They are very proud to illustrate that the restricted lanes are moving faster than the general purpose lanes (GPL).  And that buses are moving faster as a result.  However, when you consider that the vast majority of the cars in the restricted lanes are now solo drivers instead of 2-person carpools, they are actually moving far fewer people.

The bus service is slightly faster than the old HOV lane, but the overall capacity has been decimated.  The math is simple. 2-person carpools were removed from the restricted lanes for 8 hours of the day.  They have been replaced by solo drivers.  Meanwhile, the number of people in vanpools and buses has increased only slightly and those vehicles still only make up about 5% of all the people using the restricted lane. In fact there are only about 5 buses/hr during peak on I-405 north of SR522 and far less off-peak.  In other words, there is little difference in the 3+ vehicles before and after converting from 2+ to 3+.  That leaves only the change in 2-person carpools which is a decrease of on average 850 people per hour.  That is the equivalent of 10 fully-packed buses every hour.


Sadly, a single HOV 2+ lane could allow buses to move just as fast as they are going today if only WSDOT had built the HOV lane with the 4 foot separation from the GPL as is recommended by the AASHTO (chapter 3).

What’s more is that a 2 person carpool typically does not use any spaces at a park and ride because they meet at one of the rider’s home.  Buses and vanpools have the added cost of still requiring everyone to drive and park somewhere and wait for their ride. That is part of the hidden cost of 3+ modes of transit.

Posted in Uncategorized
One comment on “FHWA Changes the definition of Congestion
  1. Bill Popp, Sr says:

    Great depictions but a little speculative in places and especially at the end with the car pool formation logic. There are probably 10-15% 3+ car pools in the original HOV stream. But for a simple message it’s okay except I can’t follow the math. Your list of ways to reduce congestion are sound of course.

    Did FHWA really change their definition of congestion?

    Actually the main reason for the HOV lanes was to improve transit reliability and thus transit use — increased person throughput is a potential result of that.



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