Case Studies in Performance-Based Analysis of Geometric Design

1. Apply ISATe to compare the relative computed crash frequency
and severity among each alternative. The effort was completed
in five primary steps:
ROSE QUARTER SAFETY ANALYSIS FOR OREGON DOT
ˆˆ Determine the difference in expected safety performance of three alternatives for a
2-mile stretch of I-5 in Portland, Oregon.
ˆˆ Efficiently apply the HSM Freeway Prediction Methodology developed in NCHRP
Project 17-45 to determine the relative performance of the three alternatives in an
accelerated time period.
ˆˆ Integrate safety performance in project decision-making using a relative comparison
among alternatives.
TRANSPORTATION RESEARCH BOARD
2016 ANNUAL MEETING
Andrew Butsick, KAI
Brian L. Ray, KAI
Presented by:
ˆˆ Observe the expected
differences in crash frequency
and severity on segments and
ramps.
ˆˆ Understand the components
of each alternative that were
contributing to relative crash
performance.
ff ISATe tool shows resulting
CMFs for various geometric
design elements.
ˆˆ Compare relative safety
performance of alternatives on
an accelerated timeline. This
approach is appropriate for a
comparative evaluation method.
ODOT developed three alternatives for a 2-mile section of I-5 through
Portland, Oregon to address merging/weaving conflicts, improve lane
continuity, and improve operational and safety performance. The difference
in relative safety performance was used as one of the factors for ODOT to
consider when selecting a preferred alternative.
ASSUMPTIONS AND EFFICIENCIESASSUMPTIONS AND EFFICIENCIES
BACKGROUNDBACKGROUND
METHODOLOGYMETHODOLOGYPROJECT OBJECTIVESPROJECT OBJECTIVES
RESULTS ALLOWED THE TEAM TO:RESULTS ALLOWED THE TEAM TO:
SPECIFIC ASSUMPTIONS AND EFFICIENCIES USED:
ff Assume shoulder rumblestrips on the freeway mainline in all alternatives.
ff Using the northbound geometry from the Single Braid Alternative for all three
alternatives to reduce computations.
ff Apply consistent design assumptions to all three alternatives for consistency.
ff Exclude all northbound ramps due to consistent geometry among
alternatives.
ff Exclude two ramps serving the southbound direction at Broadway.
ff Exclude cross-ramp terminals.
ff Exclude no-build analysis since the focus was understanding the potential
differences between potential Build alternatives.
1. Data Acquisition: Extract specific data
needed at a planning-level to distinguish
safety performance between alternatives.
2. Segmentation: Identify segments based on changes in:
ff Number of through lanes
ff Lane width
ff Shoulder width
ff Median width
ff Barriers
ff Gore points
3. Geometric Data Collection: Apply Google Earth tools to expedite data
collection of geometric features.
4. Calculations:
ff Calculate curve information from radius and length information from the
planning-level designs.
ff Compute the proportion of AADT during high-volume hours (Phv) for each
segment of each alternative using AADT hour-of-data distribution. The value
varied by segment and alternative, capturing the impact of congestion on
the predicted crash frequency and severity.
5. Data Entry: Apply the ISATe tool, using efficiencies where
possible, to expedite the process for comparing the alternatives.
Jim Bonneson, KAI
Ashleigh Griffin, KAI
Jon Makler, ODOT
Supported by:
Session 446: Case Studies on Performance-Based Analysis of Geometric Design
Assumptions or exclusions where alternatives did not differ expedited the
safety evaluation process.