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4. LIFE CYCLE COST ANALYSIS

LCCA was performed to compare the demonstration bridge to a conventional cast-in-place (CIP) concrete deck bridge of the same size that would be typical for the location of the demonstration bridge. The following sections summarize the methodology and assumptions used to complete the analysis, along with a summary of the results.

LCCA ASSUMPTIONS AND SUMMARY OF RESULTS

The formula in figure 29 was used to calculate the LCCA for both options:

Figure 29. Equation. LCCA formula
Figure 29. Equation. LCCA formula

Where:
FC = First (Initial) Cost
t = Time Period of Analysis
MC = Maintenance Costs
IC = Inspection Costs
FRC = Future Rehabilitation Costs
S = Salvage Values or Costs
pwf = Present Worth Factor
UC = Users Costs

The life cycle cost consists of the summation of all costs incurred over the life of the structure discounted to account for the use of constant dollars. These costs include the initial design and construction costs, periodic maintenance and inspection costs, future rehabilitation costs, any residual value or salvage value, and the user costs associated with all of the previously mentioned activities. The discount rate is represented by the present worth factor, and for this analysis a value of 3 percent was used (typical established values range from 3 to 5 percent). All costs for the LCCA were gathered from actual costs recorded during the demonstration project construction or best professional estimates by the Iowa DOT, Wapello County, or the contractor.

The user costs for both options were compiled using the information shown in table 4, and a spreadsheet prepared by the Pennsylvania DOT available for public use was modified and used to complete the computations.

LCCA summaries for the demonstration bridge and the CIP option are shown in tables 5 and 6, respectively. The LCCA for both options turned out to be similar after all costs were considered.

Table 4. User costs for the demonstration bridge and the CIP bridge
User Cost Inputs Demonstration Bridge CIP Bridge
Length of affected roadway (miles)* 3.00 3.00
Average Daily Traffic* 280 280
Normal traffic speed (mph) 45 45
Construction traffic speed (mph) 45 45
Normal accident rate (per million vehicle miles) 1.9 1.9
Construction accident rate (per million vehicle miles) 2.2 2.2
Number of construction days 120 130
*Total traffic affected by maintenance, inspection, and rehabilitation activity.

As shown in tables 5 and 6, the CIP bridge has a slightly lower life cycle cost than the demonstration bridge. There are a few main causes:

  • The initial cost of the demonstration bridge is high. A large initial cost is difficult to overcome and is the biggest cause for uncertainty about UHPC. If the initial cost for the UHPC option could be decreased, the LCCA would favor this option easily.

  • The amount of traffic using the bridge is relatively small. The user costs associated with maintaining and rehabilitating the CIP bridge are one of the main reasons the LCCA is close to being equal for both options. However, the amount of traffic using the bridge on a rural secondary road is considerably less than what would be found on a highway or interstate. If this bridge were placed on a road with double the daily traffic, the LCCA would favor the demonstration bridge.

  • The maintenance and rehabilitation costs for the CIP bridge occur far enough in the future that the costs are discounted substantially to convert to today’s dollar value. While the CIP bridge requires considerably more maintenance than the demonstration bridge, the costs occur at 25, 50, and 100 years in the future. Due to the discount rate, these costs are reduced to a small value in terms of today’s dollars. This limits the effect of maintenance costs in the overall LCCA.

Based on the results of the LCCA, it appears the UHPC waffle deck system would be ideally suited for use on a heavily traveled road where impacts to users would be minimized by the shorter construction time and decreased maintenance activity.

Table 5. Summary: Demonstration LCCA bridge
Demonstration Bridge
ITEM COST NOTES
Initial Costs $498,017 Actual Recorded Cost of Construction (Provided by Wapello County)
Annual Maintenance $250 / Year Estimated Yearly General Maintenance (Provided by Wapello County)
Inspections (Required Every Two Years) $175 Estimated Inspection Cost
(Provided by Wapello County)

Five Year Increment Scheduled Maintenance
Crack Repair, Patching, Joint Sealant (Inspect / Repair / Replace)

$250 / Occurance This item is Not Needed on UHPC Bridge

25 Year Scheduled Maintenance
Surface Grinding and Overlay

$0 This item is Not Needed on UHPC Bridge

50 Year Scheduled Maintenance
Redeck Bridge

$0 This item is Not Needed on UHPC Bridge

75 Year Scheduled Maintenance
Surface Grinding and Overlay

$0 This item is Not Needed on UHPC Bridge

100 Year CIP Design Life Reached
Demolish and Rebuild CIP Bridge

$0 This item is Not Needed on UHPC Bridge
120 Year UHPC Design Life Reached
End of Useful Life - No Residual Value
$0 Assume girder life is extended by 20 years due to fewer deck rehabilitation and less damage from corrosion due to poor deck conditions.
User Costs Associated with Construction and Maintenance
Consist of Driver Delay Costs, Vehicle Operating Costs, and Accident Costs
$168,702 (Calculated from data provided by IDOT)
TOTAL LIFE CYCLE COST $680,270

 

Table 6 Summary: CIP LCCA bridge
Estimated Cost of a Similiar Bridge with CIP deck
ITEM COST NOTES
Initial Costs $375,642 Estimated Cost of Construction with Typical CIP Desk Design (Provided by Wapello County / IDOT)
Annual Maintenance $250 / Year Estimated Yearly General Maintenance (Assume slightly more than UHPC) (Provided by Wapello County)
Inspections (Required Every Two Years) $200 / Occurance Estimated Inspection Cost (Assume slightly less than UHPC) (Provided by Wapello County)

Five Year Increment Scheduled Maintenance
Crack Repair, Patching, Joint Sealant (Inspect / Repair / Replace)

$1,000 / Occurance  

25 Year Scheduled Maintenance
Surface Grinding and Overlay

$25,000 (Provided by IDOT)

50 Year Scheduled Maintenance
Redeck Bridge

$45,000 (Provided by IDOT)

75 Year Scheduled Maintenance
Surface Grinding and Overlay

$25,000 (Provided by IDOT)

100 Year CIP Design Life Reached
Demolish and Rebuild CIP Bridge

$375,642 Assumed Typical Service Life of CIP Bridge is 100 Years
120 Year UHPC Design Life Reached $0 Not Applicable to the CIP Bridge
120 Year Residual Value of CIP Bridge $297,313 Credit for 80 years of useful life remaining in the structure (Calculate from construction cost - future maintenance costs)
User Costs Associated with Construction and Maintenance
Consist of Driver Delay Costs, Vehicle Operating Costs, and Accident Costs
$233,842 (Calculated from data provided by IDOT)
TOTAL LIFE CYCLE COST $662,756

CONCLUSIONS

The final design is anticipated to perform well in service.

Casting was a successful experience for Coreslab Structures. The demonstration bridge panels were produced with ease due to the experience of Phase 1.

Construction of the demonstration bridge proceeded smoothly, considering the new construction techniques that were required.

The testing on the completed structure validates the assumptions from Phase 1 testing.

Only minor cracking was observed adjacent to the abutment in the demonstration bridge that poses no threat to the long-term durability of the structure.

The LCCA relating to the UHPC waffle deck system is suited for a roadway where user costs can be decreased by construction speed and reduced maintenance delays.

Overall, the project has been a successful experience, and invaluable knowledge has been gained relating to the application of UHPC in bridge construction.

Page last modified on June 13, 2013.
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