I-35W’s MnPASS lane, where vehicles can frequently enter and exit the high-occupancy toll lane, is just as safe as the MnPASS lane on I-394, where motorists only have a few shots to enter the system, a new study finds.
Researchers at the Minnesota Traffic Observatory undertook the MnDOT-funded study because of objections to open systems like the one on 35W.
“The federal government has very strong arguments against the open system. They’re saying it’s going to be dangerous – cause more disruption and more congestion,” said John Hourdos, director of the Minnesota Traffic Observatory. “We found that both roadways are working very well today because they were designed appropriately for their location.”
The definition of an open system is one that has more opportunity for access than restriction. On 35W, a dotted white lane means vehicles can enter the toll lane at will, and a solid line bars access.
Vehicles must have two occupants on-board or an electronic pay card to use the express lanes during rush hour.
The reason I-35W allows vehicles to enter MnPASS more frequently than I-394 is because there are more ramps where new vehicles are entering the freeway and might want to get on MnPASS.
Researchers studied whether accidents are more likely to occur by studying the number of accident-inducing vehicle movements along the 35W corridor. They found that areas where accidents are mostly likely to occur are also where the lane would have to allow access anyway under a closed system like 394.
The study also looked at mobility, determining that MnPASS users have just as good free-flowing traffic under the open system.
Researchers also created design tools that engineers can use to determine where access points should be on MnPASS lanes.
Until now, engineers have relied on rule of thumb. For example, the general guidance for allowing access on a closed system was 500 feet for every lane between the entrance ramp and the HOT.
The tools can be used to automatically determine how fluctuations in the MnPASS fee will affect congestion within the lane.
The fee to use MnPASS depends on the time of day.
As the express lane become more congested, the fee to use it increases. This slows the number of cars entering the lane, increasing the speed of the vehicles already in the lane.
“We ran the tool on three locations on 35W and found that, for example, on Cliff Road, you can increase the traffic by 75 percent and still be okay,” Hourdos said. “You have more leeway there than north of the crossroads of Highway 62 and 35W, for instance.”
- MnPASS Express Lanes: Open or Closed Access? — Technical Summary (PDF, 1 MB)