Part-time shoulder simulated to decrease travel time by up to 1.86 minutes per kilometer along congested segments of Philadelphia interstate.

The impact, though significantly larger than previous experiments' results, is dependent on intersection geometry and traffic density.

Date Posted

Operational Evaluation of Part-Time Shoulder Use for Interstate 476 in the State of Pennsylvania

Summary Information

Part-time shoulder use, or PTSU, is a capacity-increasing strategy in which the road shoulder is temporarily utilized during peak commuting periods. It sees sporadic application in the United States, predominantly for transit. As a dynamic lane management strategy that helps to address issues of limited land availability for permanent arterial expansions, it is likely to become increasingly relevant and effective as connected vehicles make more flexible management possible.

This paper consists of a literature review and a simulation-based implementation of PTSU along a stretch of I-476 in Philadelphia. Several different scenarios were tested to determine if limiting the PTSU lane to either passenger vehicles or heavy trucks would be more effective than simply being an additional general-use lane. While PTSU lanes are frequently bus-only, there are no transit routes along the selected segment.


  • The overall travel time reductions were found to range from 0 to 1.86 minutes per kilometer of road. This is notably greater than the literature's overall range of impacts, which were 0.05 to 0.62 minutes per kilometer.
  • The two most congested segments in the study were found to have a travel time reduction of 1.08 to 1.86 minutes per kilometer.
  • The most effective implementation was found to be the scenario in which only passenger cars were permitted on the PTSU lane. This is likely because an additional lane for heavy trucks would introduce merging issues at interchanges.

Overall, it was found that the addition of a PTSU lane provided statistically significant improvements to travel time. However, these benefits varied based on the geometry of certain intersections and ramps. Though significant for both directions of traffic, the effects of PTSU were much stronger for northbound traffic given its higher congestion.

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