3. Methodology and Data Collection
3.1 Purpose of Evaluation
Evaluations of transportation projects have three main purposes: to compare alternatives, to measure a project's worth, and to determine if a project's goals are being met. Researchers often use evaluation results to identify areas of improvement and to select alternatives that ensure a project meets intended goals. The Federal Highway Administration suggests four reasons to evaluate an ITS system and places each on a timeline as shown in Figure 3.1.
Figure 3.1 Four Reasons to Evaluate ITS Systems - Adapted from Federal Highway Administration (13)
The Federal Highway Administration (13) also hypothesizes that evaluations often focus on the first step of quantifying the impacts of a project. Less often, system evaluations are compared to other evaluations to provide a matrix of choices that may help make future investment decisions. ITS systems in particular are only occasionally evaluated for system optimization and operation refinement purposes. To understand the full impacts of a system, evaluations should be designed for all three purposes.
3.2 Data Collection
Data collection for Salt Lake City's I-15 followed the measure of effectiveness (MOE) analysis method. The measures of effectiveness incorporated into the analysis were based on typical HOV evaluation measures including: volume, speed, travel time, violation, and vehicle occupancy. The freeway TMS sites provided large automated data for volume and speed. Travel time, violations, and vehicle occupancy were based on manual field surveys. Data collection included time periods before the HOV lanes opened, after they opened in May of 2001, and recurring measures throughout the first year of operation.
3.2.1 Location of Data Collection
To investigate the effectiveness of the HOV system, person and vehicle volumes are analyzed at specific sites along the HOV corridor. The results are compared with those of GP lanes during a.m. and p.m. peak periods in the peak travel direction. These measures determine whether the HOV lane is enhancing the person-carrying capacity of the system and the extent to which a HOV lane is being utilized. The locations and data collected include:
Vehicle Occupancy
- four locations along I-15 to provide data representative of the corridor
- one location at I-215 East (4500 South)
- one location at I-215 West (3100 South)
Travel-times / Volume Counts / Speeds
- I-15 (five morning and five afternoon peaks)
- I-215 East (five morning and five afternoon peaks)
- I-215 West (three morning and three afternoon peaks)
- Traffic monitoring stations (TMSs)
Volume Counts / Speeds
- I-15 (3 morning and 3 afternoon peaks)
- I-215 East (3 morning and 3 afternoon peaks)
- I-215 West (3 morning and 3 afternoon peaks)
- Traffic monitoring stations (TMSs)
HOV Violation Data
HOV violation data was collected at the 400 South HOV on/off ramp. Vehicle occupancies were collected for traffic entering and exiting I-15 from both directions. It was noted whether or not the vehicles qualified for HOV lane use. Data was collected in fifteen-minute intervals for one and a half hours in the p.m. peak period on a recurring monthly basis. HOV lane violation data was also collected at representative locations along the I-15 corridor.