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Vertical curves are parabolic transitions that connect different grades on highways and railroads, ensuring a smooth alignment between back and forward tangents. The back tangent represents the initial grade, while the forward tangent defines the subsequent grade. These curves can be symmetrical, with equal tangent lengths, or nonsymmetrical, with varying lengths. The key points defining a vertical curve include the Point of Vertical Intersection (P.V.I.), where the tangents meet; the Point of...
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Redefining ramp influence area for curved diverging and merging freeway segments using crash data.

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  • 1Department of Civil and Construction Engineering, Western Michigan University, 1903 W. Michigan Ave, Kalamazoo, MI 49008, United States.

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Summary

This study introduces a data-driven method to define freeway ramp influence areas (RIAs) based on geometry, revealing that crash risk varies significantly by ramp type and alignment, leading to more accurate safety assessments.

Keywords:
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Area of Science:

  • Transportation Engineering
  • Traffic Safety Analysis
  • Roadway Geometry

Background:

  • Freeway Ramp Influence Areas (RIAs) are typically defined by fixed distances, which may not accurately reflect heterogeneous crash patterns.
  • Driver behavior, roadway geometry, and traffic operations significantly impact crash risk near ramps.

Purpose of the Study:

  • To develop and validate a data-driven framework for empirically delineating RIAs based on crash data.
  • To identify ramp-specific crash influence distances (τ) that account for geometric variations.

Main Methods:

  • Utilized Negative Binomial Generalized Additive Models (NBGAMs) to model crash frequency based on ramp characteristics.
  • Employed Negative Binomial gradient boosting (XGBoost) and change-point analysis with spatial bootstrap resampling to determine influence distances.

Main Results:

  • Crash influence distances (τ) varied significantly by ramp geometry: curved entry ramps (≈1,800 ft), straight entry ramps (≈300-1,000 ft), curved exit ramps (≈500-900 ft), and straight exit ramps (≈300 ft).
  • Demonstrated directional asymmetry: merging ramp disturbances diffuse downstream, while diverging ramp disturbances dissipate rapidly.
  • Established a geometry-dependent hierarchy of ramp influence.

Conclusions:

  • The proposed data-driven framework offers a more accurate method for defining RIAs compared to fixed buffer distances.
  • Geometry-specific thresholds enable improved safety assessments and freeway ramp design.
  • Supports flexible, risk-based RIA delineation for enhanced crash mitigation in complex environments.