Background on Atlanta I-85 HOV to HOT Conversion

The conversion of HOV lane to HOT lane has been implemented in 15 miles of Atlanta I-85 (from Chamblee Tucker Road to Old Peachtree Road) on Oct, 1 2011.  I-85 is a heavily commuter-oriented facility, with heavy traffic into (southbound) Atlanta during the morning peak travel period, and out of (northbound) Atlanta in the evening peak.  The previous HOV lanes were well traveled during peak periods, that there is little space available to offer to additional vehicles, whether HOV or toll paying.  Speeds in the HOV lane drop to 45 mph during the peak hour in the peak direction of travel under previous conditions, or in other words, the HOV lanes were operating roughly at capacity during peak periods in the peak direction. HOT lane system expansion is under consideration throughout the Atlanta metro region (HOV Strategic Implementation Plan Atlanta Region, 2003).

Before the Atlanta I-85 HOV to HOT conversion, HOV users had to have two or more passengers per vehicle to be able to use the lane (HOV2+).  However, after the conversion to a HOT facility, registered vehicles carrying three or more persons (HOT3+) as well as buses, vanpools, motor cycles, alternative fuel vehicles, and on-call emergency vehicles are allowed to use the lane for free.  Because 3-person carpools are more difficult to form than 2-person carpools, the demand for free use of the lane significantly decreases.  The resulting capacity on the lane is then sold to 2-person carpools and single occupant vehicles (SOVs) that are willing to pay a toll to use the lane. 

Before the conversion, people had to choose between general purpose lanes and HOV lane which required two or more passengers per vehicle.  After the conversion, solo drivers have a choice of two options: those who choose to pay the toll enjoy a faster trip in the HOT lane, while drivers who choose not to pay the toll may use the congested general purpose lanes for free.  Carpoolers on the other hand can use the HOT lane for free if the vehicle meets the minimum occupancy requirement (HOT3+ in I-85).  The travel choice before and after the conversion varies by traveler and the same travelers can easily make a different decision on any given trip due to the constraints of that particular trip.