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November 19, 2017
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The link between driver turnover and motor carrier safety

Comment
While it makes sense that an increase in driver turnover would have a negative effect on the carriers' safety, little is known about the exact nature of the relationship and about whether managers can take steps to mitigate those negative effects.

THE ARTICLE
"How does driver turnover affect motor carrier safety performance and what can managers do about it?" by Jason W. Miller of Michigan State University, John P. Saldanha of West Virginia University, Manus Rungtusanatham of The Ohio State University, and Michael Knemeyer of The Ohio State University. Published in the September 2017 issue of the Journal of Business Logistics.

THE UPSHOT
Truck driver turnover—the rate at which drivers voluntarily and involuntarily leave their jobs—and motor carrier safety are big concerns for the trucking industry and shippers who use trucking services. However, relatively little is known about the effect of turnover on safety. While it makes sense that an increase in driver turnover would have a negative effect on the carriers' safety, little is known about the exact nature of the relationship and about whether managers can take steps to mitigate those negative effects.

To answer those questions, Dr. Jason Miller of Michigan State University and his fellow researchers utilized a multimethod research design where they first surveyed managers at for-hire U.S. motor carriers, and then combined that information with data on carriers' safety violations that are publicly available from the U.S. Federal Motor Carrier Safety Administration (FMCSA). Analysis of the data found that the relationship between driver turnover and safety is not linear. Rather, a given percentage-point increase in driver turnover has a more pronounced negative effect on the rate of safety violations for a carrier with a low rate of driver turnover than it has on one with a high rate of driver turnover. The research also found that having formal rules and standard operating procedures for drivers and centralizing decision-making can mitigate the negative effect of driver turnover on some (but not all) facets of motor carrier safety.

Miller, the article's lead author, spoke with Supply Chain Quarterly Senior Editor Susan Lacefield about the practical implications of these findings.

What was the impetus for your research?
This research formed one of the three essays of my Ph.D. dissertation. I decided to examine the issue of how driver turnover related to motor carriers' rates of safety violations because 1) there has been limited empirical work on the topic despite its importance; 2) people have generally assumed that this relationship is linear, by which I mean a 1 percentage-point increase in turnover has the same negative effect on safety regardless of a carrier's baseline turnover rate; and 3) there is limited understanding concerning whether managers can mitigate the presumed negative consequences [of the relationship] between turnover and safety.

What did your research show about the link between driver turnover and motor carrier safety performance?
This research finds evidence that an increase in carriers' driver turnover rates results in worse performance for the "unsafe driving," "hours-of-service compliance," and "vehicle maintenance" safety metrics tracked by the FMCSA. However, for all three metrics, we find that the relationship is highly nonlinear, such that a 1 percentage-point increase in driver turnover has a far more pronounced negative effect when a carrier has a low baseline rate for turnover (for example, 20 percent annually) versus when a carrier has a high baseline rate for turnover (for example, 100 percent). We further found that when carriers determine how drivers execute work activities—what we term "activity control" in our paper—it helps to mitigate the negative consequences of increases in driver turnover on the unsafe driving measure.

Can you provide some examples of activity controls that can improve motor carrier safety?
Activity control represents the extent that the carriers' managers shape how drivers execute their tasks. This includes things such as scheduling work (for example, trying to prevent drivers from operating during the riskiest nighttime hours), establishing standard operating procedures for drivers to follow (for example, how pre-trip inspections should be conducted, how to alert dispatchers of drivers' locations, etc.), and determining what routes drivers should follow.

So companies that have such activity controls in place are able to reduce the negative consequences of turnover on some aspects of safety?
Activity control only mitigates the consequences of driver turnover on unsafe driving; it does not reduce the negative consequences of driver turnover on hours-of-service compliance or vehicle maintenance. In retrospect, this finding makes sense in that we would expect activity controls to more strongly influence drivers' in-cab operations, which are a direct cause of unsafe driving behaviors. In contrast, compliance with hours-of-service rules and maintenance are more directly influenced by carrier-level actions. Thus, activity control is not a panacea that can address all of the negative safety consequences arising from driver turnover.

Were there any other findings from the research that may be surprising or interesting to supply chain professionals?
One thing we found was that higher levels of driver turnover were negatively related to carrier safety for the three metrics tracked by the FMCSA (unsafe driving, hours-of-service compliance, and vehicle maintenance) that we utilized in our study. I had anticipated that this effect would only hold for unsafe driving and hours-of-service compliance, given that these two metrics are under the control of a carrier's drivers to a greater extent than vehicle maintenance is. This just goes to show the importance of addressing turnover.

The research also showed that driver turnover displayed a very strong nonlinear relationship with each of the safety metrics, which indicates that the carriers that should be most worried about a 1 percentage-point increase in turnover are, somewhat paradoxically, those with lower baseline turnover rates. The explanation we offered for this set of findings is that firms with a high baseline turnover rate are likely to have developed routines that help mitigate the consequences of turnover, such that a 1 percentage-point increase in turnover has limited impact on their operations. In contrast, for firms that tend to experience far lower turnover rates, a 1 percentage-point increase in turnover is far more disruptive.

What are some ways managers—both those who work for motor carriers and those who hire motor carriers—can apply the findings of your research?
Motor carrier managers can gain a better understanding of how reducing driver turnover is likely to improve their safety as well as a better understanding of when increases in turnover are likely to be the most detrimental to safety. Shippers can use carriers' data on driver turnover to develop better forward-looking projections of carriers' safety.

Our research further lends credence to the recent report by the National Academies of Sciences, Engineering, and Medicine (NASEM) that urged the FMCSA to collect more detailed information regarding carriers' operating characteristics that could affect their safety. Driver turnover was mentioned in this report as an area warranting data collection. The findings reported in our research corroborate the NASEM's recommendation.

What do you think the key takeaway from your research is for practitioners?
Driver turnover negatively affects carriers' safety across a variety of safety dimensions measured by the Federal Motor Carrier Safety Administration as part of the Compliance, Safety, and Accountability (CSA) program. But this relationship is highly nonlinear, in that a 1 percentage-point increase in driver turnover has a more pronounced negative effect on safety for carriers that have lower baseline rates of driver turnover. Thus, when practitioners evaluate the benefits from reducing turnover, they need to also incorporate costs that stem from lower safety compliance in addition to recruitment and training costs.

Editor's Note: CSCMP members can access JBL articles by clicking on the "Develop" tab at cscmp.org, selecting "Journal of Business Logistics," and using the secure link to the Wiley Online Library.

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