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Mandatory speed limits and crash frequency on motorways — A causal machine learning approach

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  • Metz-Peeters, Maike

Abstract

This study analyzes the effects of binding segment-level speed limits on injury crash frequencies on German motorways. Various geo-spatial data sources are merged to a rich novel data set, providing detailed information on 500-meter segments of large parts of the network. A causal forest is applied to estimate effects under fairly weak assumptions about the underlying data generating process and to offer insights into effect heterogeneity. Furthermore, the study explores potential biases through a phenomenon called spatial overfitting and examines potential solutions. Substantial negative effects of three levels of speed limits on crash frequencies are found, particularly for crashes involving severe or fatal injuries, while effects on crashes involving light injuries are comparably small. The heterogeneity analysis suggests larger crash rate reductions on roads with less traffic, as well as on roads with entrance and exit ramps, while heterogeneity regarding shares of heavy vehicle traffic is inconclusive.

Suggested Citation

  • Metz-Peeters, Maike, 2025. "Mandatory speed limits and crash frequency on motorways — A causal machine learning approach," Transportation Research Part A: Policy and Practice, Elsevier, vol. 200(C).
    • Handle: RePEc:eee:transa:v:200:y:2025:i:c:s0965856425002447
    DOI: 10.1016/j.tra.2025.104616
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    JEL classification:

    • C21 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables - - - Cross-Sectional Models; Spatial Models; Treatment Effect Models
    • H10 - Public Economics - - Structure and Scope of Government - - - General
    • R41 - Urban, Rural, Regional, Real Estate, and Transportation Economics - - Transportation Economics - - - Transportation: Demand, Supply, and Congestion; Travel Time; Safety and Accidents; Transportation Noise
    • R48 - Urban, Rural, Regional, Real Estate, and Transportation Economics - - Transportation Economics - - - Government Pricing and Policy

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