Compare Driving Algorithms Using Hard-Braking Rates

Quick Overview

Design an exposure-aware experiment comparing hard-braking rates across two driving algorithms, with city and road-condition controls and count-data inference.

Compare Driving Algorithms Using Hard-Braking Rates

Company: Waymo

Role: Data Scientist

Category: Analytics & Experimentation

Difficulty: medium

Interview Round: Technical Screen

You are comparing two autonomous-driving algorithms. The available table records algorithm, city, road-condition category, miles driven, and hard-braking count. For this exercise, comfort is determined only by hard braking: fewer hard-braking events for comparable driving exposure indicate greater comfort. Design an experiment and a statistical analysis to compare the algorithms. Explain how mileage, city, road conditions, and the distribution of hard-braking counts affect your design, and identify what the existing table cannot establish by itself. ### Constraints and Clarifying Questions - Clarify what one row represents: a trip, a vehicle over a period, or an aggregate of multiple drives. - Define hard braking consistently across algorithms and decide whether miles are comparable measures of exposure under different road conditions. - Clarify whether algorithms were assigned randomly and whether the same vehicles or routes contribute repeated observations. - No sample size, count distribution, improvement target, or assignment mechanism is supplied. State any statistical model as a hypothesis to check. - The task is to design and analyze an experiment; a database query alone does not answer it. ```hint Keep the exposure with the count Two drives can have the same number of hard-braking events but very different mileage. Also consider what happens when an algorithm receives most of the difficult-road mileage. ``` ### What a Strong Answer Covers - A comfort metric, estimand, and comparison direction that account for driving exposure. - An assignment plan and analysis that address city and road-condition differences without confusing stratification with randomization. - A suitable starting model for count data, diagnostics for overdispersion or excess zeros, and inference that respects repeated observations. - An effect estimate and uncertainty interval, plus limitations of observational or aggregated data. ### Follow-up Questions - What would make a simple Poisson model inappropriate for these counts? - How would your conclusion change if one algorithm were tested mostly in easier road conditions? - What additional identifiers would you collect if rows from the same vehicle were correlated? - How would you plan the experiment when hard-braking events are rare and many rows contain zero events?

Overview: Design an exposure-aware experiment comparing hard-braking rates across two driving algorithms, with city and road-condition controls and count-data inference.

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Waymo
Sep 6, 2026
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You are comparing two autonomous-driving algorithms. The available table records algorithm, city, road-condition category, miles driven, and hard-braking count. For this exercise, comfort is determined only by hard braking: fewer hard-braking events for comparable driving exposure indicate greater comfort.

Design an experiment and a statistical analysis to compare the algorithms. Explain how mileage, city, road conditions, and the distribution of hard-braking counts affect your design, and identify what the existing table cannot establish by itself.

Constraints and Clarifying Questions

  • Clarify what one row represents: a trip, a vehicle over a period, or an aggregate of multiple drives.
  • Define hard braking consistently across algorithms and decide whether miles are comparable measures of exposure under different road conditions.
  • Clarify whether algorithms were assigned randomly and whether the same vehicles or routes contribute repeated observations.
  • No sample size, count distribution, improvement target, or assignment mechanism is supplied. State any statistical model as a hypothesis to check.
  • The task is to design and analyze an experiment; a database query alone does not answer it.

What a Strong Answer Covers Guidance

  • A comfort metric, estimand, and comparison direction that account for driving exposure.
  • An assignment plan and analysis that address city and road-condition differences without confusing stratification with randomization.
  • A suitable starting model for count data, diagnostics for overdispersion or excess zeros, and inference that respects repeated observations.
  • An effect estimate and uncertainty interval, plus limitations of observational or aggregated data.

Follow-up Questions Guidance

  • What would make a simple Poisson model inappropriate for these counts?
  • How would your conclusion change if one algorithm were tested mostly in easier road conditions?
  • What additional identifiers would you collect if rows from the same vehicle were correlated?
  • How would you plan the experiment when hard-braking events are rare and many rows contain zero events?
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