Evaluation of the Effectiveness of High Occupancy Vehicle Lanes

In May 2001, 16 mi of high-occupancy vehicle (HOV) lanes opened on the reconstructed Interstate 15 (I-15) in Salt Lake City. A single northbound HOV lane and a single southbound HOV lane are separated from the four general-purpose (GP) freeway lanes in both directions by striping that allows HOV lane entrance and exit. The HOV lanes operate 24 hours a day and allow vehicles with two or more occupants, motorcycles, and transit vehicles. The only HOV-specific access to an arterial is located at 400 South and allows HOV-only direct access to the I-15 southbound on-ramp and the I-15 northbound off-ramp. This paper reports on a two-year study evaluating HOV lane performance. The analysis assesses the freeway operations before the HOV lanes opened with continued assessment throughout the first year of operation. It looks at automatic data from traffic monitoring stations and manual data from roadside and travel time surveys. The findings indicate that during the afternoon peak period, the HOV lane moves the same number of people as each GP lane with only 44% of the vehicles. However, the HOV lane moves fewer people than its GP lane counterparts throughout the rest of the day during times of little or no congestion. HOV lanes show travel time savings for HOV users. According to measures of travel time between 400 South and 10600 South, relative to the adjacent GP lanes, the HOV lanes provide a 30% travel time savings during the afternoon peak period and a 13% travel time savings during the morning peak time. Furthermore, unlike the higher variation of travel times on GP lanes, HOV lanes provide a more consistent and predictable travel time because of lower rates of congestion and incidents. The HOV lanes' violation rates range from 5% to 13% along the I-15 corridor, which is slightly higher than the 5% to 10% expected by national averages. At the 400 South HOV on/off ramp the violation rates increase to 20%. Recurring surveys during the initial year of HOV operations show that violation rates initially reduced after the HOV lane opening and have since stabilized. Average vehicle occupancy on I-215 and non-HOV portions of I-15 have remained the same before and since the HOV lane opening. Vehicle occupancy on the I-15 corridors with HOV lanes experienced a 17% increase, from 1.1 persons per vehicle to 1.3. Therefore, public support of HOV lanes has resulted in carpooling. Though HOV lanes are successful and anticipated to be increasingly valuable as the congestion in the Salt Lake Valley increases, this report offers recommendations to improve the HOV lanes' performance.