Knowledge Resources

In Minneapolis-St. Paul, MnDOT made its MnPASS I-394 high-occupancy-vehicle (HOV) lanes available to high-occupancy toll (HOT) lane drivers. The new HOT lanes used dynamic tolling to improve travel time reliability and increase safety. By providing designated entry and exit points to the express lanes, and giving solo-drivers an option to pay for high speed travel instead of sitting in congested general purpose lanes, the system was expected to decrease the number of drivers randomly weaving through traffic to access the express lanes, and reduce the number of abrupt illegal entry and exit maneuvers that result from drivers frustrated with large speed differentials between the express lanes and general purpose lanes. In April 2005, the MnPASS HOT lanes were open to solo drivers through electronic tolling. Buses, carpools and motorcycles use the system for free.

METHODOLOGY
Models were used to estimate traffic with and without the improvement and the Empirical Bayes method was used to determine if crash rates decreased after the conversion. Four-year observations were made before the conversion and two-year observations were made after the conversion.

RESULTS

After the conversion of MnPASS, the analysis indicated that the number of crashes on I-394 decreased by approximately 5.3 percent.

In addition, after the conversion and solo drivers were given a choice to opt in, the violation rate decreased from 20 percent to 9 percent on the concurrent flow section of the I-394 MnPASS whereas the violation rate on the I-35W HOV lanes increased from 23 percent to 33 percent during the same period (Munnich, 2008).

Overall, the safety benefits for the two years following the conversion were estimated at $5 million. The benefits were substantial given that MnPASS collected about $1.2 million in tolls per year.

The authors noted that the specific design of an HOT lane and its layout with other non-HOT lanes can play an important role. Since the I-394 MnPASS HOV-to-HOT lane conversion was accompanied by designating access points, the authors were unable to differentiate the extent of benefits attributable to the pricing component. In addition, since limited studies have been done regarding the safety benefits of HOV-to-HOT lane conversion projects, they were unable to generalize results that would be transferable to other HOT lane sites.