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Publication Number: FHWA-HRT-11-024
Date: April 2011

Safety Evaluation of the Safety Edge Treatment

Chapter 5. Estimated Cost of the Safety Edge Treatment

This chapter presents the analysis results for the cost of the safety edge treatment. Section 5.1 discusses an analysis of costs for both treatment and comparison resurfacing contracts, and section 5.2 presents another method for determining the cost of the safety edge.

5.1 Comparison of Overall Costs of Resurfacing Projects

Since the safety edge treatment adds a wedge of asphalt to each edge of the roadway, it is expected to add cost to a resurfacing project. Costs of resurfacing both treatment and comparison sites were obtained from each of the participating States after the resurfacing project was completed and project accounts were finalized. The cost items obtained for each project included the engineer's estimate, the contract cost or price bid for the project by the winning bidder, and the cost per ton of the hot-mix asphalt (HMA) concrete used to resurface the roadway and form the safety edge.

The Georgia data set included 28 resurfacing projects (15 treatment and 13 comparison sites) and 345 mi of roadway. A summary of the project costs for Georgia is shown in table 29. Costs per mile of safety edge resurfacing versus non-safety edge resurfacing were found to be $110,000 versus $140,000.

Table 29. Summary of Georgia resurfacing project costs (2005).

Cost item

Weighted average cost

Nonweighted average cost

Safety edge sites

Comparison sites

Safety edge sites

Comparison

sites

Engineer's estimate ($ million/mi)

$2.650

$1.353

$3.222

$1.272

Contract cost ($ million/mi)

$1.306

$1.353

$1.183

$1.268

HMA resurfacing cost ($/ton)

$45.730

$43.050

$49.210

$42.970

HMA resurfacing cost ($ million/mi)

-

-

$0.110

$0.140

- Not applicable.

The Indiana data set included 16 resurfacing projects (8 treatment and 8 comparison sites) and 165 mi of roadway. A summary of the project costs for Indiana is shown in table 30. Costs per mile of safety edge resurfacing versus non-safety edge resurfacing were found to be $140,000 versus $150,000.

Table 30. Summary of Indiana resurfacing project costs (2005).

Cost item

Weighted average cost

Nonweighted average cost

Safety edge sites

Comparison sites

Safety edge sites

Comparison sites

Engineer's estimate ($ million/mi)

$1.878

$1.766

$1.748

$1.691

Contract cost ($ million/mi)

$1.505

$1.419

$1.407

$1.388

HMA resurfacing cost ($/ton)

$38.200

$35.510

$38.600

$35.650

HMA resurfacing cost ($ million/mi)

-

-

$0.140

$0.150

- Not applicable.

The New York data set included six resurfacing projects (three treatment and three comparison sites) and 25 mi of roadway. A summary of the project costs for New York is shown in table 31. Costs per mile of safety edge resurfacing versus non-safety edge resurfacing were found to be $30,000 versus $40,000. Costs for New York projects are substantially less than Indiana and Georgia. The HMA costs were generally higher in Indiana and Georgia than in New York, but it is also possible that the New York projects differed in scope from those in Indiana and Georgia.

Table 31. Summary of New York resurfacing project costs (2005).

Cost item

Weighted average cost

Nonweighted average cost

Safety edge sites

Comparison sites

Safety edge sites

Comparison sites

Engineer's estimate ($ million/mi)

$0.368

$0.881

$0.354

$0.737

Contract cost ($ million/mi)

$0.106

$0.145

$0.108

$0.143

HMA resurfacing cost ($/ton)

$40.290

$49.180

$40.670

$51.710

HMA resurfacing cost ($ million/mi)

-

-

$0.030

$0.040

- Not applicable.

The cost analyses for resurfacing with the safety edge treatment as compared to resurfacing projects on similar roads without the safety edge treatment were reviewed collectively and individually. A summary of the resurfacing costs for all three States combined is shown in table 32. Collectively, the cost of resurfacing with the safety edge treatment was found to be slightly less than without the safety edge treatment. Earlier analysis of the yield of coverage on safety edge and non-safety edge sites in Georgia found only a very small difference in the amount of area covered per ton of asphalt.

Table 32. Summary of combined Georgia, Indiana, and New York resurfacing project costs (2005).

Cost item

Weighted average cost

Nonweighted average cost

Safety edge sites

Comparison sites

Safety edge sites

Comparison sites

Engineer's estimate ($ million/mi)

$1.632

$1.333

$1.775

$1.233

Contract cost ($ million/mi)

$0.973

$0.973

$0.899

$0.933

HMA resurfacing cost ($/ton)

$41.407

$42.578

$42.830

$43.445

HMA resurfacing cost ($ million/mi)

-

-

$0.096

$0.110

- Not applicable.

Some advocates of the safety edge treatment maintain that incorporating the treatment in resurfacing projects has little, if any, added cost because the asphalt used is merely reformed to create the safety edge treatment. The results summarized in table 32 can be interpreted as consistent with this hypothesis. However, construction practices vary between contractors and highway agencies, and while the amount of asphalt used for the safety edge treatment may be very small, it is unrealistic to assume there is no additional cost to implement this treatment. The next section presents an alternative approach to estimating the additional cost per mile of the safety edge treatment.

5.2 Cost of Safety Edge Treatment Based on Amount of Asphalt Used

An alternative method to determine the cost of the safety edge treatment is to compute the amount of asphalt used to provide the treatment and multiply this quantity by a typical bid cost per ton of HMA for that specific project.

Figure 5 shows a typical triangular cross section for the safety edge treatment. The safety edge treatment is shown with a cross slope of 30 degrees, which is consistent with current practice. The cost per mile for the safety edge treatment on both sides of the road based on the cross section shown in figure 5 can be estimated using equation 5.

This figure shows the safety edge treatment in relationship to the new pavement overlay placed during resurfacing. The figure shows that the safety edge is an asphalt wedge with a 30 degree slope, and it shows that the height of the safety edge is designated by the variable h.

Figure 5. Diagram. Typical cross section for the safety edge treatment on one side of the road.

CC subscript SE equals A times L times D times C all over two-thousand. (5)

Where:

CCSE = cost for application of the safety edge treatment ($ per mi)

A = area of the safety edge treatment cross section (ft2) equals 0.5 parenthesis h/12 close parenthesis h slash tan 30 degress over 12.

h = height of safety edge treatment (inches)

L = length of safety edge treatment (ft)

D = HMA density (1b/ft3)

C = HMA cost ($/ton)

The height of the safety edge treatment (h) is estimated to range from 1.5 to 3.0 inches, based on the assumption that a 1.5-inch overlay will be placed and that the shoulder will be leveled between 0 and 1.5 inches below the elevation of the pavement existing before resurfacing.

The length of the safety edge treatment for a 1.0-mi road section would be 2.0 mi or 10,560 ft for both sides of the road combined.

The density of the HMA for the safety edge treatment is estimated to be 100 1b/ft3. This is less than the maximum density of compacted asphalt because the safety edge treatment is not compacted as an overlay course would be.

The cost of HMA has increased since the 2005 costs shown in table 29 through table 32. HMA costs vary substantially between regions of the United States. Based on discussions with several highway agencies, a representative current price for HMA is $75 per ton.

Applying equation 5 to the values discussed above, the cost for a safety edge treatment 1.5 inches high would be $536 per mi. The cost for a safety edge treatment 3.0 inches high would be $2,145 per mi. Thus, a reasonable range of costs for the safety edge treatment is $536-2,145 per mi.

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