The impact of HOT lanes on carpools

This research investigated the change in carpooling on U.S. roadways once high occupancy/toll (HOT) lanes began on those roadways. HOT lanes generally allow carpools to travel on the lane for free while charging a toll for single occupant vehicles (SOVs) to use the lane. In most cases these lanes were previously high occupancy vehicle (HOV) lanes where carpools traveled for free and SOVs were not allowed. Note that clean fueled SOVs were allowed in some cases. Thus carpoolers could now switch to being a SOV and still access the benefits of the HOT lane – for a toll. This may cause some carpools to break up and become SOVs, thus adding to the amount of traffic and emissions on the roadway. Carpooling on eight roadways with HOT lanes was examined. As best as possible, data on the number of carpools on the facility in the year before and the year after converting from HOV lanes to HOT lanes was examined. Overall, carpooling decreased on most of the corridors, stayed the same on a couple of corridors, and on the one corridor that added the HOT lanes (SR-91) carpooling increased. Despite these results it is still difficult to draw definitive conclusions as (a) carpool preference tends to vary by facility, (b) there were many exogenous factors also playing a role in the amount of carpooling, (c) there is inherent difficulty obtaining occupancy counts and those counts can fluctuate a great deal day to day and month to month. Overall though, it does appear that carpooling is often negatively impacted by converting a HOV lane to a HOT lane.


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  • Accession Number: 01530814
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jun 23 2014 3:46PM