Safety Score Methodology

Overview

The DK Law Service Area Traffic Safety Index provides data-driven safety rankings for 21 California cities within DK Law’s service areas. Our methodology combines multiple crash indicators from the California Office of Traffic Safety (OTS) to create a composite score reflecting traffic safety conditions in each community.

Study Parameters

Analysis Period: Most recent available year per city (2020-2023)
Geographic Scope: 21 California cities within DK Law service areas
Data Source: California Office of Traffic Safety (ots.ca.gov)
Update Frequency: Annual (pending OTS data releases)

Cities Included

Los Angeles, San Diego, San Jose, San Francisco, Fresno, Sacramento, Long Beach, Bakersfield, Anaheim, Riverside, Irvine, Moreno Valley, Rancho Cucamonga, Victorville, Costa Mesa, Whittier, Newport Beach, Buena Park, Cerritos

Data Source

All crash statistics are sourced exclusively from the California Office of Traffic Safety (OTS) Crash Rankings database, which compiles data from SWITRS (Statewide Integrated Traffic Records System). OTS provides consistent, publicly verifiable data across all California cities.

Scoring Methodology

Core Safety Metrics

Each city is evaluated across three key traffic safety dimensions:

1. Crash Rate Score (40% Weight)

Formula: Crash Rate per 1,000 = (Total Fatal + Injury Victims / City Population) × 1,000

What it measures: Overall crash exposure risk adjusted for population size. This metric captures the likelihood that a resident will be involved in a traffic crash resulting in death or injury.

Why 40% weight: As the broadest measure of traffic safety and the only metric capturing crash frequency on a per-capita basis, this metric receives the highest weight.

2. Impaired Driving Score (35% Weight)

Formula: DUI Percentage = (Alcohol-Involved Crashes / Total Crashes) × 100

What it measures: Prevalence of alcohol or drug-impaired driving as a contributing factor in crashes.

Why 35% weight: Impaired driving crashes tend to be more severe and are highly preventable. This weighting reflects both the severity correlation and the importance of this metric for personal injury case evaluation.

3. Vulnerable Road User Score (25% Weight)

Formula: VRU Percentage = ((Pedestrian + Bicycle Crashes) / Total Crashes) × 100

What it measures: Risk to pedestrians and bicyclists—the most vulnerable road users who face the highest severity outcomes when involved in crashes.

Why 25% weight: While critical for understanding complete traffic safety, this metric receives slightly lower weight because it measures crash composition rather than overall frequency.

Score Calculation

Each metric is normalized to a 0-100 scale using min-max scaling within the 21-city dataset:

Normalization Formula:
Score = 100 × (Max Value – City Value) / (Max Value – Min Value)

Note: Higher scores indicate safer conditions (inverse relationship with risk)

Composite Safety Score

The final Traffic Safety Score is calculated as the weighted sum of all three normalized metrics:

Composite Score = (Crash Rate Score × 0.40) + (DUI Score × 0.35) + (VRU Score × 0.25)

Scores range from 0 (least safe) to 100 (safest), providing an intuitive scale for public communication.

Statistical Adjustments

Winsorization

To prevent statistical outliers from skewing results, all metrics are winsorized at the 5th and 95th percentiles before normalization. This standard statistical practice ensures that unusual data points don’t unduly influence rankings while preserving genuine safety differences.

Ranking Tiers

Cities are classified into four tiers based on their composite ranking:

Tier	Rank	Classification
Tier 1	1-5	Safest
Tier 2	6-11	Moderate
Tier 3	12-16	Concerning
Tier 4	17-21	Highest Risk

Ranking Methodology

Cities are ranked from safest to least safe based on their Composite Safety Score. In cases of tied scores, the following tiebreakers are applied in order:

1. Lower crash rate per 1,000 residents
2. Lower impaired driving percentage
3. Lower vulnerable road user percentage

Important Limitations

Data Coverage

• OTS reports “Fatal and Injury” crashes as a combined figure; separate fatality rates are not available
• Data years vary by city (2020-2023, depending on OTS availability)
• Police-reported crashes may underrepresent minor incidents
• Bicycle and pedestrian incidents are particularly prone to underreporting

Normalization Scope

• Rankings are normalized within the 21 DK Law service area cities only, not against statewide benchmarks
• A city scoring 50/100 is at the median of this specific dataset, not the California median

Population Baseline

• Per-capita rates use residential population, not accounting for commuter or visitor traffic
• Cities with high tourism or commuter populations may show different effective risk profiles
• Census estimates have inherent margins of error

Interpretation Guidelines

What These Rankings Show

• Relative traffic safety performance across DK Law service areas
• Multi-dimensional view of traffic safety challenges
• Data-driven baselines for comparing communities

What These Rankings Don’t Show

• Absolute risk levels (all driving involves some risk)
• Neighborhood-level variations within cities
• Safety of specific roads or intersections
• Isolated fatality rates (due to OTS data structure)

Annual Updates

Rankings are updated annually as new OTS data becomes available, typically with a 12-18 month lag from the data year.

Last Updated: January 2026
Version: 2.0

This methodology has been reviewed by independent traffic safety experts and follows established practices in transportation safety research and epidemiological analysis.