4. HOV Lane Utilization

4.1 GP Lanes vs. HOV Lanes 24-hour Volume Profile

Throughout the Salt Lake Valley, TMSs are located along the freeways system in 800-meter intervals. The TMSs provide volume, speed, and detector occupancy data. Figure 4.1 displays an example of data collected at the 5800 South TMS site on I-15. This figure illustrates the 24-hour traffic volume profile on a typical weekday. Multiple TMS sites provided the data for the analysis of speed and volume and HOV usage along the I-15 corridor. The a.m. and p.m. peak traffic periods were identified as 6:30 to 8:30 a.m. in the northbound direction and from 4:00 to 6:00 p.m. in the southbound direction. This directional split is consistent with the I-15 HOV corridor connecting downtown Salt Lake City, the dense employment district, with the southern residential suburbs.

On a per-lane basis, the HOV lanes carried fewer vehicles in comparison to the GP lanes. During afternoon peak-use times, the traffic volumes in some GP lanes approached 2,200 vplh, the lane's maximum capacity under ideal conditions. Figure 4.1-1 also shows that the utilization of the HOV lane is higher from 3:30 to 6:30 p.m. on the I-15 Southbound, in contrast, the HOV lane volumes on the I-15 Northbound stay relatively constant from 7:00 a.m. to 7:00 p.m.

4.2 GP Lanes vs. HOV Lanes Mode Split

Figure 4.2-1 shows the vehicle classification percentages on I-15 at 3900 South during the peak periods. The percentage of vans and buses on the HOV lane is higher than on the GP lanes. The express buses operated by Utah Transit Authority (UTA) frequently use this HOV facility during peak periods. Buses comprise 2.5 percent of traffic on the HOV lanes, and only 0.1 percent traffic on the GP lanes. Figure 4.2-1 shows the percentages of people that buses, cars, and vans carry on I-15 at a sample 3900 South location during the peak periods. Buses carried 27.6 percent of the people on the HOV lanes.

4.3 GP Lanes vs. HOV Lanes Throughput

Throughput refers to roadway person-movement and/or vehicle-movement on HOV and GP lanes. It is necessary to analyze both person and vehicle throughput in order to evaluate a HOV lane. Three representative I-15 sites located at 2700 South, 3900 South, and 5800 South were selected for detailed manual analysis. Selection was based on points of interest, availability, and usability of manually collected data as well as TMS data.

Figures 4.3-1 through 4.3-2 depict several pieces of throughput information for each representative site. The The Average Vehicle Occupancy (AVO) and the vehicle and person throughput data for GP and HOV lanes are also presented in overall and per-lane statistics in Figure 4.3-3.

According to Figure 4.3-3 data, on a per-lane analysis, the northbound HOV lane carried 1,766 persons during a two-hour period in the a.m. peak period. Compared with the GP lanes, the HOV lane carried 52.2 percent fewer people and 76.3 percent fewer vehicles. During the two-hour p.m. peak period, the southbound HOV lane carried almost the same number of people as a GP lane, but with 56.2 percent fewer vehicles. As anticipated, the HOV lane displays its value during the more congested periods.

4.4 HOV Lane Usage During the 2002 Winter Olympic Games

The 2002 Salt Lake City Winter Games were the largest Winter Olympic Games ever held. They included 78 events in 15 disciplines and seven sports. More than 1.5 million tickets were sold for the Olympic events and more than 500,000 visitors attended the Games. These numbers created unprecedented travel needs in Salt Lake City. The I-15 corridor with HOV lanes played an important role during the Olympic Games, providing the greatest amount of freeway capacity in the Salt Lake Valley.

More than one month's worth of continuous traffic monitoring was conducted before, during, and after the Olympic Games (14). HOV lane usage was analyzed based on a comparison between traffic during and after the Olympic Games. The 24-hour overall transportation demand during the Games was only 15 percent higher than after the Games. This is attributed to most people in the Salt Lake area operating with either a working break, a modified schedule, or increased rideshare efforts during the Olympic Games. It resulted from a great effort on the part of engineers, planners, and Olympic coordinators to inform the public of the coming traffic and the need to reduce typical commuter demand during the two-week Olympic period. These preparations were estimated to reduce the background traffic along I-15 by up to 40 percent. In Table 4.4-1 a sample location shows that 24-hour traffic volumes on the HOV lanes during the Olympics were 16 to 18 percent higher than after the Olympics while the GP lanes increased only by to 4 percent. This increase in HOV usage can be attributed to travel behavior changes. More local travelers carpooled, less commuter traffic was on the road due to work schedule shifts, and visitors tended to occupy multi-rider vehicles. The time-saving advantages of the HOV lanes enticed carpoolers to utilize them. Many of the events were held in the downtown area at night. This resulted in a new peak traffic period from 9 to 11 p.m., as shown in Figure 4.4-1. Therefore, the HOV facilities, together with efficient public transportation systems, including the Light Rail TRAX, the Olympic bus, and the regular bus, reduced traffic congestion during the Olympic Games.

Table 4.4-1 24-hour Traffic Volume Changes at I-15 5800 South between, during, and after Olympic Games

Traffic volume unit: vehicles/per lane/per day