Responding to safety concerns regarding access to MnPASS express lanes, researchers at the University of Minnesota Traffic Observatory (MTO) evaluated two types of lane designs to see if one was safer than the other. Results indicate, however, that lane design has little impact on traffic mobility or safety.
The study looked at MnPASS facilities on I-35W and I-394. On I-394, the MnPASS lanes are largely separated from the general-purpose lanes by a double white line, meaning drivers can only enter at certain points. I-35W features more open access, meaning drivers have more opportunities to enter and exit the MnPASS lanes.
Critics have focused their attention on the I-35W lanes, which they claim create the potential for more congestion and accidents due to vehicles changing lanes more often.
Researchers evaluated the two lane designs using video data to analyze the speed and frequency of lane changes. This allowed them to identify when shockwaves—sudden stoppage or slowdown of traffic—occurred. Shockwave frequency was the standard for impact on mobility, and shockwave length was used to measure safety.
Ultimately, the study found that shockwave activity was similar between both lane designs, and actually slightly higher on the restricted-access lanes of I-394.
MTO researchers were also able to use the study to create a tool to predict the relationship between traffic levels and shockwave activity.