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Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

Author

Listed:
  • Reza S. Shirazinejad

    () (Department of Civil Engineering, Kennesaw State University, 655 Arnston Drive, Marietta, GA 30062, USA)

  • Sunanda Dissanayake

    () (Department of Civil Engineering, Kansas State University, 2118 Fiedler Hall, Manhattan, KS 66506, USA)

  • Ahmed Jalil Al-Bayati

    () (Kimmel School of Construction Management, Western Carolina Univ., Cullowhee, NC 28723, USA)

  • David Daniel York

    () (Kimmel School of Construction Management, Western Carolina Univ., Cullowhee, NC 28723, USA)

Abstract

In the summer of 2011, a change in the Kansas laws came into effect, increasing the speed limit on a selected set of freeway sections from 70 mph to 75 mph. Higher speeds were thought to have economic benefits, mostly because the travel time reduction means people reach their destinations more quickly. In this study, the sections where the speed limits remained unchanged, are compared to freeway sections that have been influenced by speed limit increase, to evaluate safety effectiveness. The study utilizes the before-and-after study with comparison group method to assess the safety effects provided in the Highway Safety Manual (HSM). Two crash datasets, obtained by considering three years before and three years after the speed limit increase, were compared in order to evaluate the safety effects of the speed limit change. The crash modification factors (CMFs) were estimated, which showed that there was a 27% increase in total crashes and a 35% increase in fatal and injury crashes across all sections after the speed limit change, and these increases were statistically significant at 95% confidence level. These confounding results show that the speed limit increase has not been beneficial for traffic safety in Kansas, and hence it is important to be cautious in such future situations. Also, additional data have been presented which would be beneficial in identifying and understanding any behavior change in drivers following a speed limit increase.

Suggested Citation

  • Reza S. Shirazinejad & Sunanda Dissanayake & Ahmed Jalil Al-Bayati & David Daniel York, 2018. "Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach," Sustainability, MDPI, Open Access Journal, vol. 11(1), pages 1-15, December.
  • Handle: RePEc:gam:jsusta:v:11:y:2018:i:1:p:119-:d:193370
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    More about this item

    Keywords

    speed limit increase; before-after study; fatal and injury crashes; freeways; safety evaluation; crash modification factors;

    JEL classification:

    • Q - Agricultural and Natural Resource Economics; Environmental and Ecological Economics
    • Q0 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - General
    • Q2 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Renewable Resources and Conservation
    • Q3 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Nonrenewable Resources and Conservation
    • Q5 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Environmental Economics
    • Q56 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Environmental Economics - - - Environment and Development; Environment and Trade; Sustainability; Environmental Accounts and Accounting; Environmental Equity; Population Growth
    • O13 - Economic Development, Innovation, Technological Change, and Growth - - Economic Development - - - Agriculture; Natural Resources; Environment; Other Primary Products

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