How and Where GP vs. HOV Throughput Was Measured

To investigate the effectiveness of the HOV system, person volumes per lane per hour were analyzed at specific sites along major HOV corridors during morning and afternoon peak periods in the direction of the heaviest traffic flow. The results were then compared with the identical location, direction, and time periods for the GP lanes. Person volumes were estimated by combining vehicle volumes with vehicle occupancy data (the number of people in each vehicle) collected manually by the University of Washington for WSDOT, and, then adding transit ridership data provided by the various transit agencies (King County Metro, Pierce Transit, Community Transit, and Sound Transit). Because a typical freeway has only one HOV lane and several GP lanes, GP lane throughput was determined by dividing the total volume of all GP lanes by the number of GP lanes. This provided a per-lane average for comparative purposes.

HOV lane person volumes were estimated at ten sites on the major freeway corridors (I-5, I-405, SR 520, I-90, SR 167) in the central Puget Sound area.  The sites selected are representative of the person volumes carried by the HOV lanes on specific sections of the various HOV corridors. The data are presented for the following locations:

How to Read GP vs HOV Throughput Graphs

These graphs present summary information on the directional peak period vehicle and person volumes present on both general purpose and HOV lanes at selected central Puget Sound region locations. The upper graphs show the percentage of all vehicles and travelers at a given site that are traveling on the HOV lane or on GP lanes.Data are presented for the primary commute movement.

The lower graphs also compare person and vehicle volumes on GP and HOV lanes, but on a per lane basis. The columns represent the average number of persons or vehicles per GP or HOV lane (numerical values are shown on each column).  The percentages in the HOV columns indicate the percentage difference in the number of people or vehicles carried in the HOV lane in relation to those in an average GP lane at the same location.  For example, an HOV person volume percentage of +70 percent indicates that at that site, the HOV lane carries on average 70 percent more people than the average GP lane.  AVOHOV and AVOGP are the average number of people per vehicle in an HOV or GP lane, respectively. 

As with other graphs on this website, the AM peak period graphs include data for three hours, from 6:00 AM to 9:00 AM.  The graphics for the PM peak period include data for four hours, 3:00 PM to 7:00 PM.  These graphs also indicate how many lanes of each type are present at each location.  For example, the label “HOV-1, GP-3” indicates that one HOV lane and three general purpose lanes are present.