Safety Evaluation of Edge-Line Rumble Stripes on Rural Two-Lane Horizontal Curves

Chapter 8. Economic Analysis

The project team conducted an economic analysis to estimate the B/C ratio for this strategy on rural two-lane horizontal curves. For the purposes of the economic analysis, the assumed treatment was the application of ELRSs. The project team used the recommended CMFs of 0.75 for Kentucky and 0.79 for Ohio to estimate the benefit of this treatment strategy. The Ohio results likely included the impact of additional sign upgrades, which were not provided or considered in this analysis. In addition, the cost of pavement markings was not considered in the study because these markings were already present on the roadway and the ELRSs did not affect the lifespan of edge-line pavement markings. Treatment costs ranged from $1,700/mi for Ohio to $2,500/mi for Kentucky. For Kentucky, service life was estimated as 12 to 15 years. For Ohio, ODOT noted that the service life was as long as the pavement life, which was assumed as 7 to 10 years. A conservative value of 12 years was assumed for Kentucky and 7 years for Ohio.

The FHWA Office of Safety Research and Development suggested using the Office of Management and Budget’s Circular A-4 to determine the conservative real discount rate of 7 percent.⁽⁴¹⁾ This value was applied to calculate the annual cost of the treatment for 12- and 7‑year service lives in Kentucky and Ohio, respectively. With this information, the capital recovery factor was computed to be 7.94 for a 12-year service life and 5.39 for a 7-year service life.

At the time of this report, the most recent FHWA mean comprehensive crash costs disaggregated by crash severity, location type, and speed limit were based on 2001 dollar values.⁽⁴²⁾ The 2001 unit costs for property damage only and fatal and injury crashes from the FHWA report ($7,428 and $158,177, respectively) were multiplied by the ratio of the 2014 (when the analysis was performed) value of a statistical life of $9.2 million to the 2001 value of a $3.8 million.^(43,44) The project team applied this ratio of 2.42 to the unit costs for property damage only and fatal and injury crashes. The results were weighed by the frequencies of these two crash types in the after period to obtain aggregate 2014 unit costs for total crashes for Kentucky and Ohio. The resulting values were $128,268 and $166,603, respectively.

The total crash reduction was calculated by subtracting the actual crashes in the after period from the expected crashes in the after period had the treatment not been implemented. The number of crashes saved per mile-year was 0.812 in Kentucky and 0.913 in Ohio. These numbers were obtained by dividing the total crash reduction by the number of after period mile-years per site.

The annual benefit (i.e., crash savings) of $104,165 in Kentucky and $150,368 in Ohio was the product of the crash reduction per mile-year and the aggregate cost of a crash (all severities combined). The B/C ratio was calculated as the ratio of the annual benefit per mile to the annual cost per mile. The B/C ratio was estimated as 331:1 in Kentucky and 477:1 in Ohio. USDOT recommended a sensitivity analysis be conducted by assuming values of a statistical life of 0.57 and 1.41 times the recommended 2014 values.⁽⁴³⁾ These factors were applied directly to the estimate B/C ratios to obtain a range of 189:1 to 467:1 for Kentucky and 272:1 to 672:1 for Ohio. On first inspection, the B/C ratios were larger than would reasonably be expected for an installation of this type. However, the installations took place on corridors, while the analysis only examined the safety effects on horizontal curves. Horizontal curves have higher crash rates than overall corridors, and the cost per mile of installation would not be representative for installations only on horizontal curves. As a curve-specific treatment, the B/C ratio would likely be reduced owing to the higher installation cost; however, these results suggest that the treatment can be highly cost effective.