Safety Evaluation of the Safety Edge Treatment
Chapter 6. BenefitCost Analysis
This chapter presents the results of a benefitcost analysis
of the safety edge treatment based on the results in this report. Section 6.1
presents the overall approach for determining benefitcost estimates, section 6.2
documents the components of the analysis, and section 6.3 discusses the results
of the benefitcost analysis.
6.1 BenefitCost Analysis Approach
The benefitcost ratio for the safety edge treatment has been
determined according to equation 6:
_{} (6)
Where:
B/C = benefitcost ratio
N_{FI} = number of fatal and injury crashes per mile per year before application of
the safety edge treatment
N_{PDO} =
number of PDO crashes per mile per year before application of the safety edge
treatment
E_{SE} = effectiveness (percent reduction in crashes) for
application of the safety edge treatment
C_{FI} = cost savings per
crash for fatal and injury crashes reduced
C_{PDO} = cost savings per
crash for PDO crashes reduced
(P/A, i, n) = uniform series present worth factor
i = minimum attractive rate of return
(discount rate), expressed as a proportion (i.e., i = 0.04, for a discount rate of 4 percent)
n = service life of safety edge treatment (years)
CC_{SE }= cost for
application of the safety edge treatment (dollars per mile)
6.2 Components of the BenefitCost Analysis
The following sections document
the components of the benefitcost computation, including crash
frequencies, treatment effectiveness, crash costs, service life, minimum
attractive rate of return, uniform series present worth factor, and treatment
cost.
6.2.1 Crash Frequencies
Crash frequencies per mile per year were estimated for the benefitcost analysis using the SPFs presented in section 4.2. Only twolane highway
sites were considered because no treatment effectiveness measure was found for multilane highway sites. Both Georgia
and Indiana SPFs were used because
each State has an SPF and because using the individual State SPFs constitutes
a sensitivity analysis of the
results. The location of the SPFs used in the benefitcost analysis are shown
in table
33.
Table 33. SPFs used in benefitcost analysis.
State 
Roadway type 
Shoulder type 
Crash type and security level 
Table 
Georgia 
Twolane highway 
Paved 
All crashes 
10 
Georgia 
Twolane highway 
Paved 
F&I crashes 
10 
Georgia 
Twolane highway 
Paved 
PDO crashes 
10 
Indiana 
Twolane highway 
Paved 
All crashes 
11 
Indiana 
Twolane highway 
Paved 
F&I crashes 
11 
Indiana 
Twolane highway 
Paved 
PDO crashes 
11 
Georgia 
Twolane highway 
Unpaved 
All crashes 
10 
Georgia 
Twolane highway 
Unpaved 
F&I crashes 
10 
Georgia 
Twolane highway 
Unpaved 
PDO crashes 
10 
Indiana 
Twolane highway 
Unpaved 
All crashes 
11 
Indiana 
Twolane highway 
Unpaved 
F&I crashes 
11 
Indiana 
Twolane highway 
Unpaved 
PDO crashes 
11 
F&I = Fatal and injury.
PDO =
Propertydamageonly. 
The computation of crash frequencies was performed as
illustrated in the following example of Georgia twolane highways with paved
shoulders. This example illustrates the computation of crash frequencies per mile
per year for highways with a traffic volume of 1,000 vehicles per day.
SPF for total crashes from table
10:
N_{TOT} = exp (8.921 +
1.108 ln (1,000)) = 0.282 crashes per mi per year
SPF for fatal and injury crashes from table 10:
N_{FI} = exp (7.818 +
0.853 ln (1,000)) = 0.146 crashes per mi per year
SPF for PDO crashes from table
10:
N_{PDO} = exp (11.414 +
1.349 ln (1,000)) = 0.123 crashes per mi per year
Since the sum of N_{FI} (0.146) and N_{PDO} (0.123) is less than N_{TOT} (0.282), the values of N_{FI} and
N_{PDO} are adjusted so that this sum is equal to N_{TOT}, as
follows:
N_{FI} (adjusted) = 0.282 _{} = 0.153 crashes per mi per year
N_{PDO} (adjusted) = 0.282 _{} = 0.129 crashes per mi per year
6.2.2 Treatment Effectiveness
Based on the results of
the EB evaluation presented in section 4.3.2, the crash reduction effectiveness
of the safety edge treatment is 5.7 percent. Continuing the computational
example for Georgia twolane highways with
paved shoulders and a traffic volume of 1,000 vehicles per day, the crash
reduction from the safety edge treatment would be estimated as follows:
For fatal and
injury crashes:
0.153 (0.057) = 0.008721 crashes reduced per mi per year
For PDO
crashes:
0.129 (0.057) = 0.007353 crashes reduced per mi per year
6.2.3 Crash Costs
The estimated crash costs
used in this analysis are based on those currently used in SafetyAnalyst,
as follows:

Fatal crash = $5,800,000.

A injury crash = $402,000.

B injury crash = $80,000.

C injury crash = $42,000.

PDO crash = $4,000.^{(8)}
The costs are based on the
latest published FHWA values.^{(10)} The weighted average cost of a
fatal and injury crash (assuming 1 percent
fatal crashes, 9 percent A injury crashes, 50 percent B injury crashes,
and 40 percent C injury crashes) is $150,980 per crash. Based on these crash
costs, the estimated annual crash reduction benefits for the example presented
above are as follows:
0.008721 (150,980) + (.007353) (4,000) = $1,346 per mi
6.2.4 Service Life
The service life of the safety edge treatment is estimated to
be 7 years, the same as the service life of a typical pavement resurfacing
project.
6.2.5 Minimum Attractive Rate of Return
The minimum attractive rate of return for this analysis is
estimated to be 4 percent. This value is currently
used in SafetyAnalyst and is representative of the real, longterm cost of
capital (i.e., not including inflation).^{(8)}
6.2.6 Uniform Series Present Worth Factor
The uniform series present worth factor is applied to convert
the annual crash reduction benefits to a present value. This factor is
determined as shown in equation 7:
(7)
The uniform series present worth factor for a minimum
attractive rate of return of 4 percent and a service life of 7 years is
determined as follows:
(P/A, 4%, 7) = = 6.002
6.2.7 Treatment Cost
The cost of the safety edge treatment is estimated as falling
in the range of $536 to 2,145 per mi for both sides of the road combined, as
explained in section 5.2.
6.2.8 Benefit Cost Ratio
The value of the benefitcost ratio is computed using equation
6. For the computational example previously presented, the maximum benefitcost
ratio (estimated for the minimum treatment cost of $536 per mi) is determined
as follows:
B/C = _{} = 15.07
The minimum benefitcost ratio for the same case (estimated
for the maximum treatment cost of $2,145 per mi) is determined as follows:
B/C = _{} = 3.77
The result indicates that the safety edge treatment provides at
least $3 in benefits for each dollar spent
on the treatment and possibly as much as $15 in benefits for each dollar spent
on the treatment depending on the thickness of the safety edge treatment
provided. This example addresses sites with a traffic volume of 1,000 vehicles
per day. Larger benefitcost ratios would be expected for sites with higher
traffic volumes.
6.3 BenefitCost Analysis Results
The results of the
benefitcost analysis are summarized in table
34 through table
37 for application of the safety edge treatment to
four types of roadways.
Table 34. Benefitcost analysis
for application of safety edge treatment
on Georgia twolane roadways with paved shoulders.
AADT (vehicles/day) 
1,000 
5,000 
10,000 
15,000 
20,000 
Crash Frequencies 
Total
crashes per mile per year 
0.282 
1.675 
3.611 
5.659 
7.784 
F&I
crashes per mile per year 
0.146 
0.575 
1.039 
1.469 
1.877 
PDO
crashes per mile per year 
0.123 
1.079 
2.748 
4.748 
6.999 
F&I
crashes per mile per year (adjusted) 
0.153 
0.583 
0.991 
1.337 
1.646 
PDO
crashes per mile per year (adjusted) 
0.129 
1.093 
2.620 
4.322 
6.138 
Safety BenefitsNumber of Crashes Reduced 
F&I
crashes reduced per mile per year 
0.009 
0.033 
0.056 
0.076 
0.094 
PDO
crashes reduced per mile per year 
0.007 
0.062 
0.149 
0.246 
0.350 
Safety BenefitsDollars 
F&I
crash reduction benefits per year ($) 
1,314 
5,015 
8,528 
11,505 
14,165 
PDO
crash reduction benefits per year ($) 
29 
249 
597 
986 
1,399 
Total
crash reduction benefits per year ($) 
1,344 
5,264 
9,126 
12,491 
15,565 
Present
value of total benefits per year ($) 
8,065 
31,597 
54,773 
74,972 
93,421 
Treatment Cost 
Minimum cost
of safety edge treatment ($ per mile) 
536 
536 
536 
536 
536 
Maximum cost
of safety edge treatment ($ per mile) 
2,145 
2,145 
2,145 
2,145 
2,145 
BenefitCost Ratio 
Minimum benefitcost
ratio 
3.8 
14.7 
25.5 
35.0 
43.6 
Maximum benefitcost
ratio 
15.0 
59.0 
102.2 
139.9 
174.3 
F&I = Fatal and injury.
PDO =
Propertydamageonly. 
Table 35. Benefitcost analysis for application of safety edge treatment
on Indiana twolane roadways with paved shoulders.
AADT (veh/day) 
1,000 
5,000 
10,000 
15,000 
20,000 
Crash Frequencies 
Total
crashes per mile per year 
0.664 
2.175 
3.626 
4.888 
6.043 
F&I
crashes per mile per year 
0.158 
0.444 
0.694 
0.900 
1.082 
PDO
crashes per mile per year 
0.542 
1.722 
2.832 
3.789 
4.659 
F&I
crashes per mile per year (adjusted) 
0.150 
0.446 
0.713 
0.938 
1.139 
PDO
crashes per mile per year (adjusted) 
0.514 
1.729 
2.912 
3.950 
4.904 
Safety BenefitsNumber of Crashes Reduced 
F&I
crashes reduced per mile per year 
0.009 
0.025 
0.041 
0.053 
0.065 
PDO
crashes reduced per mile per year 
0.029 
0.099 
0.166 
0.225 
0.280 
Safety BenefitsDollars 
F&I
crash reduction benefits ($) 
1,291 
3,841 
6,138 
8,072 
9,804 
PDO
crash reduction benefits ($) 
117 
394 
664 
901 
1,118 
Total
crash reduction benefits ($) 
1,408 
4,235 
6,802 
8,973 
10,922 
Present
value of total benefits ($) 
8,453 
25,419 
40,824 
53,856 
65,553 
Treatment Cost 
Minimum cost
of safety edge treatment (per mile) 
536 
536 
536 
536 
536 
Maximum cost
of safety edge treatment (per mile) 
2,145 
2,145 
2,145 
2,145 
2,145 
BenefitCost Ratio 
Minimum benefitcost
ratio 
3.9 
11.9 
19.0 
25.1 
30.6 
Maximum benefitcost
ratio 
15.8 
47.4 
76.2 
100.5 
122.3 
F&I = Fatal and injury.
PDO =
Propertydamageonly. 
Table 36. Benefitcost analysis
for application of safety edge treatment
on Georgia twolane roadways with unpaved shoulders.
AADT (veh/day) 
1,000 
5,000 
10,000 
15,000 
20,000 
Crash Frequencies 
Total
crashes per mile per year 
0.377 
1.822 
3.588 
5.335 
7.068 
F&I
crashes per mile per year 
0.144 
0.673 
1.307 
1.927 
2.538 
PDO
crashes per mile per year 
0.226 
1.151 
2.320 
3.496 
4.676 
F&I
crashes per mile per year (adjusted) 
0.147 
0.672 
1.293 
1.896 
2.487 
PDO
crashes per mile per year (adjusted) 
0.231 
1.150 
2.296 
3.439 
4.581 
Safety BenefitsNumber of Crashes Reduced 
F&I
crashes reduced per mile per year 
0.008 
0.038 
0.074 
0.108 
0.142 
PDO
crashes reduced per mile per year 
0.013 
0.066 
0.131 
0.196 
0.261 
Safety BenefitsDollars 
F&I
crash reduction benefits ($) 
1,263 
5,782 
11,126 
16,314 
21,403 
PDO
crash reduction benefits ($) 
53 
262 
523 
784 
1,045 
Total
crash reduction benefits ($) 
1,316 
6,044 
11,649 
17,098 
22,447 
Present
value of total benefits ($) 
7,898 
36,277 
69,920 
102,624 
134,730 
Treatment Cost 
Minimum cost
of safety edge treatment (per mile) 
536 
536 
536 
536 
536 
Maximum cost
of safety edge treatment (per mile) 
2,145 
2,145 
2,145 
2,145 
2,145 
BenefitCost Ratio 
Minimum benefitcost
ratio 
3.7 
16.9 
32.5 
47.8 
62.8 
Maximum benefitcost
ratio 
14.7 
67.7 
130.4 
191.5 
251.4 
F&I = Fatal and injury.
PDO =
Propertydamageonly. 
Table 37. Benefitcost analysis for application of safety edge treatment
on Indiana twolane roadways with unpaved shoulders.
AADT (veh/day) 
1,000 
5,000 
10,000 
15,000 
20,000 
Crash Frequencies 
Total
crashes per mile per year 
0.409 
1.263 
2.053 
2.728 
3.338 
F&I
crashes per mile per year 
0.118 
0.235 
0.317 
0.376 
0.426 
PDO
crashes per mile per year 
0.336 
1.027 
1.662 
2.202 
2.689 
F&I
crashes per mile per year (adjusted) 
0.106 
0.236 
0.329 
0.398 
0.456 
PDO
crashes per mile per year (adjusted) 
0.302 
1.028 
1.725 
2.330 
2.882 
Safety BenefitsNumber of Crashes Reduced 
F&I
crashes reduced per mile per year 
0.006 
0.013 
0.019 
0.023 
0.026 
PDO
crashes reduced per mile per year 
0.017 
0.059 
0.098 
0.133 
0.164 
Safety BenefitsDollars 
F&I
crash reduction benefits ($) 
916 
2,027 
2,827 
3,428 
3,926 
PDO
crash reduction benefits ($) 
69 
234 
393 
531 
657 
Total
crash reduction benefits ($) 
985 
2,261 
3,221 
3,959 
4,583 
Present
value of total benefits ($) 
5,914 
13,572 
19,331 
23,762 
27,507 
Treatment Cost 
Minimum cost
of safety edge treatment (per mile) 
536 
536 
536 
536 
536 
Maximum cost
of safety edge treatment (per mile) 
2,145 
2,145 
2,145 
2,145 
2,145 
BenefitCost Ratio 
Minimum benefitcost
ratio 
2.8 
6.3 
9.0 
11.1 
12.8 
Maximum benefitcost
ratio 
11.0 
25.3 
36.1 
44.3 
51.3 
F&I = Fatal and injury.
PDO = Propertydamageonly.
For each State and roadway
type, benefitcost analyses were performed for traffic volumes ranging
from 1,000 to 20,000 vehicles per day. The overall results of the benefitcost
analysis are shown in figure
6 and figure
7.
Figure 6. Graph. Minimum benefitcost ratios for the safety edge treatment
as a function of AADT.
Figure 7. Graph. Maximum benefitcost ratios for the safety edge treatment as a function of AADT.
For twolane highways
with paved shoulders, application of the safety edge treatment has minimum
benefitcost ratios ranging from 3.8 to 43.6
for Georgia conditions and from 3.9 to 30.6 for Indiana conditions. For
twolane highways with unpaved shoulders, the minimum benefitcost ratios for the safety edge treatment range from 3.7 to 62.8
for Georgia conditions and 2.8 to 12.8 for Indiana conditions. In all these cases, the maximum
benefitcost ratios are at least four times the minimum benefitcost
ratios.
These results suggest that the safety edge treatment is
highly costeffective under a broad range of conditions. Even though there is
uncertainty in the treatment effectiveness estimate, the safety edge treatment is likely to be a good safety
investment in most situations, especially for roadways with higher
volume levels, where higher crash frequencies are expected.
