Roll Stability Systems: Cost-Benefit Analysis of Roll Stability Control Versus Electronic Stability Control Using Empirical Crash Data
As market penetration of both Electronic Stability Control Systems (ESC) and Roll Stability Control Systems (RSC) increases, certain industry stakeholders believe that, despite the fact ESC has greater functionality than RSC, the higher per-unit cost of ESC may not make it as "cost-effective" as RSC. The testing of this hypothesis was identified by the American Transportation Research Institute's (ATRI) Research Advisory Committee as a top research priority for 2012. ATRI's methodology involved the collection of empirical truck crash data from actual motor carrier operations. These data included a large sample of trucks equipped with RSC, ESC or no RSS system, and documented the relevant crash types and associated costs for trucks with and without the RSS systems. The research objective was to quantify the role of RSC and ESC in crash reduction relative to the cost of each system using operational crash data.
There are two forms of RSS for large trucks, Roll Stability Control (RSC) and Electronic Stability Control (ESC). RSC is designed to primarily prevent un-tripped rollover crashes, while ESC targets both un-tripped rollovers and crashes due to yaw instability (e.g. jackknifes). These two RSS technologies have been in the market for less than ten years; however, adoption of these technologies has been relatively swift over the last five years. RSC first became available for truck tractors in 2002 and by 2007, installation rates had reached an estimated 10.5 percent of new truck tractors sold. RSC installation was expected to increase to16 percent for model year 2012 tractors. ESC was introduced three years later in 2005; by 2007, 7.4 percent of truck tractors sold were equipped with ESC. The ESC installation rate was predicted to reach 26.2 percent for model year 2012 tractors.
There is a high degree of overlap in the type of crashes that RSC and ESC can mitigate. A 2010 Insurance Institute for Highway Safety (IIHS) study found that, of all crashes that could be addressed by a full ESC system, 41 percent could also be addressed by an RSC system. When considering more serious injury and fatality crashes, this percentage increased considerably; RSC systems may address a larger proportion of fatal (65%) and injury (76%) crashes involving rollover that are also addressed by ESC systems. While the IIHS study found that RSC-relevant crashes constituted a large fraction of serious ESC-relevant crashes, researchers did not assert the value of one system as being higher than the other, as the effectiveness of either system's ability to prevent crashes was unknown.
Given the nascent state of the technology and related data collection efforts, the underlying studies that informed the ESC FMVSS were based on controlled field tests, as opposed to empirical operational crash data. There is currently no available large-scale RSS study that has analyzed the cost effectiveness of RSC versus ESC systems based on actual truck crash data. The ATRI research presented in this report is designed to address this data gap.
To begin the RSS data analysis, it was first necessary to establish the crash rates for trucks equipped with ESC, RSC and no RSS technology. A separate crash rate was calculated for each of the three types of crashes investigated (rollovers, jackknifes, tow/stuck). Table 1 presents the crash rates from the respondent data. These rates were determined by dividing the total number of crashes in each crash type category by the total vehicle miles traveled in that category. The per-mile crash rates were adjusted to per-100-million-mile rates for ease of presentation purposes.
Table 2 displays the average cost per mile (transformed to average cost per 1,000 miles traveled for ease of display purposes). These figures represent the actual costs carriers in the sample paid for each type of crash among trucks equipped with each RSS configuration.
Similar to the crash rates calculated in Table 1, Table 2 indicates that vehicles equipped with both RSC and ESC had lower crash costs per mile than vehicles without an RSS system. While trucks without an RSS system incurred an average of $9.58 in rollover crash costs per 1,000 miles, RSC-equipped trucks only generated $3.77 in rollover costs per 1,000 miles and ESC-equipped trucks experienced $4.81 in average rollover costs per 1,000 miles.
System Installation Cost
Another critical factor in the cost effectiveness of RSS systems is the technology cost. Based on the responses, the average cost for an RSC system was $467.18. An ESC system cost, on average, $1,180.88. This indicates that, on average, ESC technology costs were 152.8 percent higher than RSC in the sample data. Using the crash costs found in Table 2, a straightforward return on investment estimation for an RSC and ESC system can be calculated. This was performed by comparing the crash cost of RSC and ESC to a baseline, namely vehicles without any RSS technology. Table 3 presents the cost savings of RSS systems from the two types of crashes analyzed along with the breakeven point based on average system cost.
|Baseline (No RSS Crash Cost / 1,000 mi)|
|- Average Crash Cost / 1,000 mi|
|= Crash Cost Savings / 1,000 mi|
|Average System Cost|
|Mileage to Breakeven Point|
Contrary to findings in several earlier studies, this analysis of operational data indicates that, for some fleets, RSC technology may be more effective, and cost-effective, at reducing rollover, jackknife and tow/stuck crashes than ESC technology.
- In the sample data, trucks equipped with RSC had lower average crash rates than trucks equipped with ESC (31.38 rollover, jackknife and tow/stuck* crashes per 100 million miles versus 40.26 crashes per 100 million miles, respectively).
- Furthermore, the research found that RSC-equipped trucks incurred lower average crash costs than ESC-equipped trucks ($4.31in rollover, jackknife and tow/stuck crash costs per 1,000 miles versus $5.27 per 1,000 miles, respectively).
- The research also found that ESC technology is 152.8 percent more expensive, on average, than RSC technology ($1,180.88 per unit versus $467.18 per unit, respectively).
- This study definitively finds that, for the industry data sample used in this analysis, RSC technology is more effective than ESC technology at preventing rollover, jackknife, and tow/stuck crashes, thus providing greater benefit to society and carriers with markedly lower installation costs.
This report, finalized in August 2012, provides additional details in the assessment of RSC and ESC using empirical crash data. These findings along with additional identified benefits provide a valuable resource for those considering the implementation of RSC and/or ESC.
In summary, relevant literature shows that both RSC and ESC are viable technologies with crash reduction potential. However, ESC technology is designed to prevent a wider array of crash types and was demonstrated in research tests to avert a larger number of incidents.
- Research determined that effectiveness rates for ESC ranged from 28 to 36 percent and from 21 to 30 percent for RSC.
- ESC was markedly more costly to adopt compared to RSC. The unit cost of RSC technology averaged $640, while ESC systems averaged $1,160.
- While research found that RSC is slightly more cost-effective than ESC, the NHTSA FMVSS proposal favors ESC over RSC as it was found to have greater societal net benefits.