6. Violations

HOV lane violations reflect public acceptance of the system. High violation rates reduce HOV lane effectiveness. HOV violation rates are not constant and vary from location to location along a facility. Figure 6-1-1 represents the average violation rate at representative locations along I-15. This graph is based upon the field data collected within the peak periods.

In general, the higher the congestion level, the higher the violation rate as SOVs are more likely to take advantage of the HOV. They perceive the benefit of violation as higher than the risk. In addition, violation rates tend to increase near points where HOV lanes merge with general purpose lanes and HOV ramps. Some motorists seem to believe that getting into the HOV lane "just a little early" is not really a violation and the short time spent in the HOV lane limits the chance that they will be observed by a highway patrol officer. For example, the violation rates at HOV lane's 400 South entrance is above 20 percent. Violation rates vary depending on the level and method of enforcement, but are typically around 10 percent according to national experience and enforcement. Concurrent flow HOV lanes typically have higher violation rates, especially at HOV ramps. The results of a more detailed investigation at the 400 South HOV ramp include monthly violation counts throughout the year as well as one-week of continuous peak hour monitoring. The results from the continuous week of observations are shown in Table 6.1-1 by direction.

Table 6.1-1 Violation Rates at HOV Lane's Ramp During Weekdays

The higher HOV ramp violations resulted in the ramp being monitored closely throughout the initial year of operation to determine how enforcement and education influenced the violations. Figure 6.1-2 shows how the violation rate changes during the initial year of HOV operations. The most dramatic change in violation rates occurred during the early stages of operation. This was indicative of early enforcement and education. The violation rate was approximately 50 percent the first month of HOV operation. Generally, the number of violations has decreased steadily from 24 percent on July 2001 to 18.7 percent the following year. However, the 18.7 percent violation is still high for a facility of this nature.

7. Average Vehicle Occupancy

Successful HOV lanes must not simply divert existing HOVs from GP lanes to the HOV lane, but must also generate new HOVs, resulting in increased AVO. According to nationwide statistics, as automobile ownership has increased, AVO from home to work trips has declined from 1.3 in 1977 to about 1.14 in 1995 (3). With the reconstruction of I-15, the increase in capacity may actually promote a decrease in occupancy by increasing available travel opportunities. Figure 7.1-1 illustrates AVO changes during peak periods before and after HOV lane operation. In order to provide a comprehensive evaluation of freeway operations throughout the Salt Lake Valley, other freeways without HOV lanes were surveyed during the same survey periods. Some of these non-HOV selected locations include I-15 and 600 North, I-215 West and 3100 South, I-215 East and 4500 South.

At the locations without HOV facilities, the AVO remained constant. In contrast, on the I-15 corridors with HOV lanes, AVO had a significant increase of twenty percent, increasing from 1.1 to 1.3. The meaningful increase in AVO, contrasted with a national decline of AVO, suggest that the HOV lane implementation has increased transit and ridesharing.