Sidewalk Grading Algorithm Overview

Algorithm Overview

The Sidewalk Scoring Algorithm is designed to evaluate sections of sidewalk within an urban environment based on various criteria critical to pedestrian accessibility. This document outlines the methodologies and grading systems used by DeepWalk’s software to prioritize and compare all inspections in the system.

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The Sidewalk Scoring Algorithm evaluates sections of sidewalk based on various criteria including cross slope, clear width, run slope, deterioration, detectable warnings and ramp presence. DeepWalk’s dataset includes a variety of measurements for each panel in a system and our goal is to prioritize and compare all inspections in the system.

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Algorithm Logic

1. The measurements from each panel are compared to threshold values to identify if there is a Minor, Moderate, Severe or Extreme accessibility violation.
2. If an accessibility violation is found, points are added to the score for that category of issue (Run Slope, Cross Slope, Detectable Warnings, etc.)
3. The score for each violation is then divided by the length of the sidewalk being inspected, then multiplied by 100
4. Accessibility Score is computed by adding the normalized scores for each violation
5. The Accessibility Score is then categorized into a 0-5 scale, with corresponding written descriptions

Data Collection

Measurements from each panel within a sidewalk system are captured using the DeepWalk Mobile Application. These measurements assess different physical characteristics crucial for determining the accessibility and safety of pedestrian pathways.

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Measurement Criteria

The data collected for each panel includes but is not limited to:

• Cross slope
• Clear width
• Run slope
• Surface deterioration
• Detectable warnings presence
• Ramp presence
• Vertical displacements

Access Score

Width Score (width_score): Score indicating severity of sidewalk clear width violations

Cross Slope Score (cs_score): Score indicating severity of sidewalk cross slope violations (slope perpendicular to the path of travel)

Percent Deterioration (percent_det): Measures the portion of the sidewalk that is deteriorated, scaled up by a factor of 10 for impact significance

Run Slope Score (rs_score): Score indicating severity of sidewalk cross slope violations (slope parallel to the path of travel)

Dectectable Warning Score (dw_score): If the scan is a ramp, 25 points are added if there is not a proper detectable warning

Mid-Block Sidewalk Access Score Formula: access_score = (width_score + cs_score + 10 * percent_det)

Curb Ramp Access Score Formula: access_score = (width_score + cs_score + 10 * percent_det + rs_score + dw_score)

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Access Grade

The accessibility score is then converted to a 0-5 Access Grade with corresponding Access Description using the below table.

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Measurement Thresholds

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Access Score Components

Accessibility Score is the precursor to the Access Grade and is computed using the below sub-formulas.

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Cross Slope Score (cs_score)

The cross slope score evaluates the slope of the sidewalk perpendicular to the path of travel. Each panel is checked for cross slope violations with varying severity levels:

• Minor: 1 point
• Moderate: 4 points
• Severe: 8 points
• Extreme: 16 points

cs_score = (Σ points from each panel / length of sidewalk) * 100

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Clear Width Score (width_score)

This score measures the clear width of the sidewalk to ensure that it is clear from obstructions, evaluated through similar severity levels:

• Minor: 5 points
• Moderate: 25 points
• Severe: 50 points
• Extreme: 100 points

The formula used is similar to the cross slope score, adjusting the point values for the perceived impact of width restrictions:

width_score = (Σ points from each panel / length of sidewalk) * 100

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Run Slope Score (rs_score)

The run slope score evaluates the slope of the sidewalk parallel to the path of travel. Each panel is checked for run slope violations with varying severity levels:

• Minor: 5 points
• Moderate: 25 points
• Severe: 50 points
• Extreme: 100 points

The formula used is similar to the cross slope score, adjusting the point values for the perceived impact of width restrictions:

rs_score = (Σ points from each panel / length of sidewalk) * 100

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Detectable Warning Score (dw_score)

If the scan is a ramp, 25 points are added if there is not a proper detectable warning

• No Detectable Warning: 25 points
• Otherwise: 0 points

Percent Deterioration (percent_det)

Calculates the proportion of the sidewalk that is deteriorated:

percent_deterioration = (sum of deteriorated areas / total area of the sidewalk) * 100

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Vertical Displacement Score (vd_score)

Adds 25 points if there is a vertical displacement (trip hazard) manual tag