8. Conclusions and Recommendations8.1 ConclusionsThe analysis and results in this report are drawn from a comprehensive evaluation of the first year of HOV lane operation on I-15. Based on the per lane analysis, HOV lanes carried nearly the same volume of people as the GP lanes and 44 percent of vehicles carried by the GP lanes during the p.m. peak time. During the rest of the day HOV lanes moved less people per lane than their GP lane counterparts. However, this is to be expected as the freeway is much less congested during off-peak times. Judging from the person throughput of HOV lanes, the HOV facility approaches its minimum pre-construction goal, which is to be able to move at least as many people as a GP lane does during the peak periods. The travel time savings and reliability available to HOV commuters include faster travel along their entire length during peak periods. Statistics show that vehicle speeds in HOV lanes were always higher than in GP lanes throughout the day. Based on the average weekday analysis, during the afternoon peak period in southbound traffic, the average speed in the HOV lane was 63.6 mph, a speed substantially greater than the 51.5 mph in GP lanes. During the morning peak period in northbound traffic, the average speed in the HOV lane was 74.0 mph, and was higher then 65.7 mph in GP lanes. Due to the difference of travel speed between HOV lanes and GP lanes, the travelers along the whole length of the HOV lane during the afternoon peak period had a 6.5 minute benefit compared to that of GP lanes. The HOV corridor p.m. peak time savings is 30.7 percent compared to the time spent in GP lanes while the morning peak period and off-peak period time savings are 13.4 percent and 4.7 percent respectively. HOV violation rates vary in different times of operation, and also in different locations of the HOV lanes. During the peak periods, the average violation rates was 20 percent at the 400 South HOV on/off ramp, which is substantially higher than violations on other segments of I-15, which range from 5 percent to 13 percent. Generally, the violation rate in the afternoon peak period, with higher levels of congestion, is higher than the morning peak period. Public acceptance of HOV lanes is judged on the number of people who shift from SOV use to transit or HOVs. After HOV lanes in the I-15 corridors had been in operation for one year, AVO had a 17 percent increase from 1.1 to 1.3. AVO on other Salt Lake Valley freeway segments without HOV lanes remained the same during the analysis period. Therefore, implementation of the HOV lanes has obtained the public support and increased the volume of carpools. 8.2 Considerations / RecommendationsThe findings indicate a successful HOV system. Relative to other urban areas where HOV lanes have been installed, Salt Lake City has relatively low congestion and therefore lower need for HOV facilities. As congestion increases, the benefits of the HOV lanes should also increase. Continued monitoring is the best way to identify and track these increasing benefits. As shown in Figure 4.1 and Figure 4.2-1, it is apparent that HOV lanes are currently underutilized. In contrast, traffic volumes in GP lanes remain consistently high between morning and afternoon peak travel times. Therefore, in the short term, opening HOV lanes to all traffic during off-peak times would more efficiently move traffic flow. However, in the long term, as congestion during off-peak times increases, the advantages to the HOV users would be eliminated. Consequently, monitoring of the system is key to adjusting policy as congestion demands. According to violation rates analysis, violations are higher than national averages, particularly at the 400 South ramps. Although the lack of barrier separation makes it difficult to enforce HOV regulations, actions such as utilizing media to educate people about HOV lane restrictions, more rigorous violation enforcement, and a program for drivers to report HOV violators, such as Seattle's HERO program, could be implemented. Compared with HOV lanes performance in other states, I-15 lanes do not meet their potential. Additional marketing of the program may increase usage, particularly if the potential travel time savings were more widely known. More public surveys of HOV users and non-users would help examine why HOV lane demand has not been higher. The most obvious reason is that the newly reconstructed I-15 simply does not have sufficient congestion to encourage large-scale use of HOV lanes. As congestion increases, usage should also. For this reason a continued monitoring effort should be made to track the HOV operations. Some states, such as Minnesota and California, have conducted continuous HOV lane evaluations since the beginning of operation. New policies are recommended to improve the efficiency of HOV lanes each year. We suggest UDOT improve its HOV data collection efforts, conduct periodic statewide surveys to determine the impact of HOV lanes on carpooling, and report on and develop a statewide plan to promote lane usage. The report should include the automated information available from the TMSs as well as vehicle occupancy and violation rate measures. The measures set forth in this study should be the data collected. These include:
This data will support HOV lane performance assessments as reported in this study. With no national guidelines on the evaluation of a HOV facility, it is important that the DOTs take it upon themselves to monitor the facilities so if public discontent occurs, as experienced in New Jersey, data is available to document the advantages of the HOV lane and discourage the "empty syndrome" argument. Statewide TMS is an important source of traffic data collection. During the process of data collection we found that only 70 percent of TMS can provide valid data in UDOT's more than 500 stations. Only 50 percent of TMSs covering the HOV lanes from 600 North to 10600 South along the I-15 corridor provided complete data, even fewer provide both reliable traffic speed data and volume data. For the continuous monitoring of HOV lanes, frequent maintenance of TMS is strongly recommended. From Figure 5.1-1, the travel speed in both HOV lanes and GP lanes drop from 7200 South to 10600 South for I-15 Southbound during the p.m. peak period. This is not surprising because three separate directions of freeway converge at the I-215 / I-15 interchange. The high volume results in recurring congestion in both HOV lanes and GP lanes. Along that segment, with only 25 percent of entire road length, more than 35 percent of travel time was spent. Much of the p.m. peak period congestions is caused by spillback from congestion at 10600 South where the HOV lane not only merges into GP lanes, but one GP lane is subtracted. A significant queuing in this segment occurs because of this road bottleneck. The primary value of the HOV lane lies in queue jumping. Making geometrical improvements, such as providing on/off ramp for HOV at the 10600 South exit or extension of HOV lanes after this point would greatly improve the travel-time-saving benefit of HOV lanes. Overall improvements to the widening of I-15 southbound from 10600 South is likely to result in reduced HOV benefits during the p.m. peak as the congestion diminishes. Consideration should be given to inside ramps for the HOV lanes as HOV users in the p.m. peak must cross four congested GP lanes to exit the freeway and therefore many potential users do not use the HOV facility for short freeway trips. As the I-15 South widening occurs in the future, inside HOV ramps at 11400 South, 12600 South, Bangerter Highway and 14400 South should be considered. Atlanta, Seattle, and Los Angeles have all incorporated direct HOV ramps for freeway-to-freeway connections and arterial connections resulting in increased utilization. References
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