Acknowledgments

The authors thank the Utah Department of Transportation employees for the data they furnished and their assistance with this study. The authors also particularly thank the Technical Advisory Committee members for their invaluable input throughout the study. The valuable contribution of those who assisted in data collection is greatly appreciated.

Disclaimer

The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented. This document is disseminated under the sponsorship of the Department of Transportation, University Transportation Centers Program, in the interest of information exchange. The U. S. Government assumes no liability for the contents or use thereof.

List of Acronyms

Executive Summary

High Occupancy Vehicle (HOV) lanes opened in the Salt Lake Valley May 14, 2001, on the reconstructed Interstate 15 (I-15). They were initially built on a 16-mile segment between 600 North and 10600 South. An 8.5-mile extension was opened between 10600 South and the Utah County line on Oct. 27, 2004. The Salt Lake Valley HOV lanes are single lanes and have a painted separation. They operate 24 hours a day, seven days a week. They operate in both the northbound and southbound directions. Two-or-more-person carpools, vanpools, buses, motorcycles, Alternative Fuel Vehicles (AFVs) and emergency vehicles are eligible to use the HOV lanes. There are inside ramps to the HOV lanes at 400 South, which is the central business district in Salt Lake City.

This study reports on the performance of the extended HOV lanes. Vehicle volume, average vehicle occupancy (AVO), modal split, person throughput, and violation rate were collected manually. Travel time and speed data were collected using the floating car method and global positioning system (GPS) software. The data collected was compared with the NCHRP standards and national averages.

The extended HOV lanes in the Salt Lake Valley are performing effectively in terms of several measures of effectiveness (MOEs) such as vehicle volume, person throughput, AVO and speed benefits. It was found that vehicle volume satisfies the NCHRP's recommended minimum vehicle volume of 400 to 800 vehicles/peak hour for the HOV lane during both the AM and PM peak hours. The NCHRP's recommended maximum operating threshold criterion of 1200 to 1500 vphpl was not exceeded during either the AM or PM peak hours.

HOV lane AVO was found to be much higher than the general purpose (GP) lane AVO during both the AM and PM peak hours. The overall AVO in the GP lane was 1.05, whereas the overall AVO in the HOV lane was 2.31. This is a strong indication of the HOV lane's effective performance. The overall peak hour AVO on I-15 was found to be 1.37 using the "average of averages method." Using the ratio of person throughput to vehicle volume, the overall peak hour AVO on I-15 was found to be 1.21.

In the GP lane, single occupant vehicles (SOVs) were the major mode, constituting 92.75 percent of all modes. In the HOV lane carpools were dominant, constituting 95.63 percent of all modes. The HOV lanes had a higher percentage of carpools, vanpools, motorcycles and buses than the GP lanes.

The NCHRP HOV Systems Manual's recommended minimum HOV lane person throughput threshold of 900 to 1,800 pphpl during the peak hours was met during both the AM and PM peak hours. HOV lane person throughput is higher during the PM peak hour than during the AM peak hour. It was found that compared to a GP lane, the HOV lane carried 18.21% fewer people with 61.97% fewer vehicles during the AM peak hour. Compared to a typical GP lane, the HOV lane carried 8.42% more people with 51.41% fewer vehicles during the PM peak hour. HOV lanes thus carry more people in fewer vehicles and are more effective during the more congested PM peak hour than during the AM peak hour when the congestion level is low.

Travel time in the HOV lane was found to be 19.75 minutes, whereas travel time in the GP lane was found to be 21.57 minutes. Travel-time savings was found to be 1.82 minutes or 8.44%. The decrease in travel-time benefits may be because of the lower levels of congestion in the GP lanes after the completion of the I-15 South project. As congestion gradually increases on I-15, the travel-time benefits of the HOV lanes are likely to increase.

The HOV lane speeds were higher than the GP lane speeds along the entire section of I-15 from 500 South to the Utah County line. Thereby the HOV lanes offer travel-time savings. Higher speeds in the HOV lanes as compared to the GP lanes indicate that the HOV lanes have less or no congestion. The HOV lane mean speeds are much higher than 45 mph which means that the HOV lane was not congested during the data collection period. Furthermore, the Salt Lake Valley HOV lane mean speed is higher than the national HOV lane mean speed of 54 mph during the peak periods.

The Salt Lake Valley HOV lane system experiences a low violation rate when compared to other cities nationally. The AM peak hour violation rate was found to be 2.59 percent. From the split of the violations it was seen that occupancy violations (SOV drivers using the HOV lanes) were the most common type of violation.

It was recommended that various managed-lane concepts need to be researched and adopted. This is most likely to optimize the performance of the Salt Lake Valley HOV lanes. There may be a need to better manage the HOV lanes through the use of other managed-lane techniques, such as pricing and reversible lanes. Improvements like direct on-ramps and off-ramps to the inside HOV lanes and prominent ILEV and carpool information signs are needed along the I-15 corridor. All these will enhance the popularity of the HOV lanes and lead to increased HOV lane use. HOV lane use in Salt Lake Valley is continuing to grow. As traffic volume in the Salt Lake Valley increases and congestion reaches higher levels, the benefits of the HOV lanes will likely increase. There is a need for continued monitoring to identify and keep track of these benefits and proactively manage the HOV lanes.