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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-14-065    Date:  February 2015
Publication Number: FHWA-HRT-14-065
Date: February 2015

 

Evaluation of Pavement Safety Performance

CHAPTER 8. BC ANALYSIS

METHODOLOGY

The BC analysis provides a method for a comparison of the various pavement treatment options. By considering the cost of each treatment, typically just the installation cost, and the benefit, quantified in terms of crash reduction and lifespan, agencies will be equipped to better justify selection of one treatment over another.

Separate analyses are provided for treatments and States for which the sample size was large enough and for which there was a statistically significant (5-percent level) benefit for total crashes. The annualized cost of the treatment is first computed using the equation in figure 35:

The  equation calculates annual cost as equal to treatment cost times discount rate  as a decimal divided by the quantity 1 minus the quantity 1 plus R, end  quantity; raised to the power of expected service life in years, end quantity.
Figure 35. Equation. Annualized cost pavement treatment.

Where:

C = Treatment cost.
R = Discount rate (as a decimal).
N = Expected service life (years).

Quantifying the actual treatment cost is one of the more difficult aspects of this analysis. Treatment costs vary widely from State to State and even within each State. Although statewide bid averages provide an estimate of the cost of the treatment itself, they do not account for any ancillary costs associated with the treatment (e.g., design, inspection, mobilization, maintenance of traffic). Therefore, calculated treatment costs were based on cost ranges published in a recent SHRP2 research report on pavement preservation treatments.(31) The SHRP2 report also provides a range for service lives of the various treatment types. For the purposes of this analysis, low-end to median values were used for service life based on a conservative assumption that rehabilitation cycle is longer than the period over which safety benefits are achieved. There is some support for this assumption in the results of the limited investigation of treatment effects over time.

Based on information from the Office of Management and Budget, the following real discount rates, based on the service life of a treatment, were used to determine the annual cost of the treatment.(46)

The most recent FHWA mean comprehensive crash costs are based on 2001 dollar values.(47) As recommended in that report, if crash costs are required for another year, the recommended adjustment procedure is to multiply the human capital costs provided in the tables by a ratio of the Consumer Price Index (CPI)-all items-for the year of interest divided by the CPI for 2001. Based on the appropriate CPI information from the U.S. Department of Labor, the ratio of the 2013 to the 2001 CPI is 230.08/175.1 = 1.314.(48) The 2001 unit costs for property damage only and fatal+injury crashes from the FHWA report were multiplied by this ratio and then weighted by the frequencies of these two crash types for a group in the after period to obtain and aggregate 2013 unit cost for total crashes.

The total crash reduction was calculated for each treatment/State group 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 year was obtained by dividing the total crash reduction by the average number of after period years per site. The annual benefit (i.e., crash savings) is the product of the total crash reduction per year and the aggregate cost of a crash (all severities combined). The BC ratio is calculated as the ratio of the annual benefit to the annual cost.

CONVENTIONAL TREATMENTS

Table 40 summarizes the results of the economic analysis of the conventional pavement treatment strategies evaluated in this study with a robust EB analysis. As noted earlier, this analysis was done for treatments and States for which the sample size was large enough and for which there was a statistically significant (5-percent level) benefit for total crashes.

Table 40 . Results of BC analysis for conventional treatment groups with statistically significant crash reductions.

Treatment (State)

Road Type

Cost/Lane-Mi

Sites

Mi

Crash Reduction per Year

Cost/ Crash

BC Ratio

Chip Seal (All)

Two-Lane

$12,320/layer (conventional)
$21,120
(rubberized or polymer-modified)

5,770

2,448

107.16

$106,905

0.69

Chip Seal
(California only)

Two-Lane

1,432

863

91.27

$107,687

2.06

Diamond Grinding (All)

Freeway

$25,570

691

141

206.67

$77,408

5.95

Thin HMA
(North Carolina only)

Multilane

$31,680

1,411

201

174.60

$74,695

3.01

OGFC (All)

Freeway

$39,000

453

165

147.90

$74,633

2.10

OGFC (North Carolina only)

105

41

184.61

$64,173

9.15

Slurry Seal (All)

Two-Lane

$15,000*

248

105

14.41

$95,587

2.25

UTBWC (All)

Two-Lane

$35,200

187

43

18.78

$96,197

3.60

*Used the cost provided by California because almost all sites are from that State
BC = Benefit-cost
HMA = Hot mix asphalt
OGFC = Open grade friction course
UTBWC = Ultrathin Bonded Wearing Course

HFS TREATMENT

Although it was not possible to conduct a rigorous EB analysis for the HFS treatments, a cursory economic analysis was undertaken based on the results in table 39 for the ramps and curves for which a comparison group study was possible. The methodology used above for the other treatments was used, with the following conservative estimates:

The results suggest the following BC cost ratios for HFS treatments:

 

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