A Tool for Designing MnPASS Access Spacing

Zitzow, Stephen; Parikh, Gordon; Hourdos, John · 2018 · ROSA P / Minnesota. Dept. of Transportation. Research Services & Library

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Summary

This research addresses the lack of a rigorous framework for designing access spacing in High-Occupancy Toll (HOT) lanes, which have traditionally relied on engineering judgment and rules-of-thumb. The study focuses on the safety and mobility implications of two design alternatives: open-access, where vehicles merge freely, and closed-access, where merging is restricted to specific "gate" locations. The primary motivation is to mitigate the safety risks associated with significant speed differentials between the managed HOT lane and congested General Purpose (GP) lanes. When vehicles merge from slower GP lanes into faster HOT lanes, they can generate shockwaves that propagate upstream, increasing the likelihood of rear-end collisions due to hard braking requirements. To address this, the researchers developed the MnPASS Access Design application, a web-based tool comprising three components: an Open-Access Module, a Closed-Access Module, and a Data Generation Module. The methodology utilizes a Monte Carlo simulation framework to reconstruct traffic streams and model shockwave generation. It incorporates the General Motors car-following model, calibrated using historical data from Minnesota freeways (I-35W and I-394), to simulate vehicle behavior and shockwave propagation. The tool integrates with existing Minnesota Department of Transportation (MnDOT) data sources, including the IRIS network configuration and detector databases, as well as simulation tools like CORSIM. The Open-Access Module estimates shockwave activity and scores the frequency of unsafe states, while the Closed-Access Module suggests optimal gate locations based on vehicle path length distributions and success rates. The study found that the tool successfully aggregates corridor-level behavior to identify locations prone to dangerous shockwave formation. By analyzing the distribution of shockwave lengths under various traffic densities and speeds, the application allows planners to determine where access restrictions are necessary to prevent unsafe lane changes. The system was validated using historical data and simulation outputs, demonstrating its ability to quantify the operational performance of HOT lanes in terms of both mobility and safety. The web interface facilitates the input of corridor geometry and traffic conditions, allowing users to compare alternative scenarios and visualize shockwave severity through color plots and histograms. The significance of this work lies in providing traffic managers with a data-driven decision-support tool for HOT lane design, moving beyond empiricism. By identifying specific zones where open access poses safety risks, the tool enables the strategic placement of closed-access segments to balance mobility with safety. This approach ensures that drivers do not attempt lane changes in areas with high shockwave potential, thereby reducing crash risks while maintaining the efficiency benefits of managed lanes. The integration with existing MnDOT infrastructure ensures the tool’s practical applicability for both existing facilities and future projects.

Key finding

The MnPASS Access Design application provides a quantitative framework for determining optimal HOT lane access spacing by analyzing shockwave distributions to identify and mitigate safety risks associated with speed differentials between managed and general-purpose lanes.

Methodology

modeling

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• work zones
• traffic density