High occupancy toll (HOT) lanes in Minneapolis/St. Paul

In May 2005, the Minnesota Department of Transportation (MnDOT) started operation of the State's first application of High-Occupancy Toll (HOT) lanes, MnPASS, on a segment of the Interstate 394 (I-394) corridor in the Minneapolis/St. Paul region. This system dynamically adjusts pricing levels from $0.25 to $8.00 in response to varying traffic conditions. The tolls are advertised through the use of Dynamic Message Signs (DMS) and paid electronically through a transponder positioned within the vehicle.

The I-394 freeway often experienced congestion prior to the MnPASS deployment. The freeway included an HOV lane that was well used but often had fewer vehicles than the available capacity resulting in the perception that the HOV lanes were underutilized. As a result, Mn/DOT implemented the conversion of the HOV lanes into a high-occupancy toll (HOT) lane operation.

The success of the MnPASS deployment in increasing utilization of the HOV lane while maintaining travel times/speeds in the HOT lanes, combined with the additional benefit of increasing speeds/decreasing travel times in the general purpose lanes, prompted Mn/DOT to explore other opportunities for deploying the dynamic pricing strategy. In 2009, HOT lanes were added to the existing HOV lane facilities located on I-35W between downtown Minneapolis and suburban Burnsville, a corridor approximately five miles in length. In 2012, this corridor was extended by approximately four additional miles further south into Burnsville. This 2012 expansion was not considered in this evaluation.

Methodology:

The I-394 and I-35W MnPASS evaluations utilized traffic data (e.g., speeds and volumes) collected primarily from automated traffic detectors in the corridor.
Data for Tuesdays, Wednesdays and Thursdays from the first week of each month was extracted. Whenever the first week included a Holiday, the second week was selected instead. The data was extracted from 4:00 a.m. to 8:00 p.m. with a 15-minute granularity. Data collection extended beyond the operational hours of the MnPASS system to capture any system effects occurring on the shoulders of the operational periods. This is an extension beyond MnPASS operational hours and sampling of three mid-week days is consistent with the original I-394 evaluation. Data collected included:

• I-394 corridor data for all years from 2006 to 2011. All of these years occur following the initial deployment of MnPASS infrastructure in mid-2005.
• I-35W corridor data from 2007 to 2011. For the assessment of the I-35W corridor, the period from January 2007 to January 2009 was designated as the baseline period (no HOT lanes), while the period from January 2009 to January 2011 was designated as the HOT lane MnPASS period.

Both the volume and speed data were assessed at individual detector stations, and for the corridor as a whole, to establish performance trends across the corridors. The statistical significance of change from the baseline was assessed using a statistical Z-Test, determined at 90- and 95-percent confidence levels. Additional data was collected on the overall MnPASS program including system usage and MnDOT costs.

Results:

Results of the initial I-394 HOT lanes evaluation include:

• The HOT lanes implementation increased corridor throughput during the peak hour by up to 5 percent. This increase occurred while regional volumes in other non-MnPASS equipped corridors observed a decrease.
• General purpose lane travel speeds increased at all study locations by an average of approximately 6 percent.
• The increase in travel speed volume reported during peak periods in the six-month period after I-394 HOT lane implementation in November 2006 has been maintained through year 2012.
• Travel times for the HOT/HOV lanes were observed to hold constant or increase slightly at all study locations, with the exception of a small portion of the corridor during the morning operational period.
• Travel speeds increased in the general purpose lanes, as well as the MnPASS lane for many locations providing an overall reduction in corridor travel times.

Results of the I-35W HOT lanes expansion evaluation:

• In the two years subsequent to implementation of I-35W HOT/HOV lanes, directional volume on the HOT lane increased by 6.5% and 9% for the AM and PM peak periods without any significant change in speed to either mainline or HOT/HOV lanes.
• The I-35W expansion resulted in increased traffic volumes and travel speeds but the benefits were not as high as with the initial I-394 deployment. However, economies of scale reduced the operating cost per transponder by 27% and the operating cost per transaction by 32%.
• System expansion resulted in fewer benefits, but at a much cheaper cost. Therefore, the overall benefit-cost ratio of expansion may outperform the initial deployment.

Additional Reference:
Cambridge Systematics (Nov 2006). I-394 MnPASS Technical Evaluation - Final Report, for Minnesota Department of Transportation. http://www.mnpass.org/pdfs/394mnpass_tech_eval.pdf