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Highways for LIFE

Arrow Bridge Replacements on MD 28 and MD 450, Frederick County and Anne Arundel County, Maryland

Economic Analysis

A key aspect of HfL demonstration projects is quantifying, as much as possible, the value of the innovations deployed. This entails comparing the benefits and costs associated with the innovative project delivery approach adopted on an HfL project with those from a more traditional delivery approach on a project of similar size and scope. The latter type of project is referred to as a baseline case and is an important component of the economic analysis. Common bridge replacement projects of this type in Maryland are traditionally performed by maintaining one lane of signalized two-way traffic. This scenario is regarded as the "baseline" for this study.

For this economic analysis, MDSHA provided all of the supporting cost figures. Unfortunately, this contract has not yet closed and the as-built cost figures are not yet available for the project due to contract management difficulties referenced earlier in the report. Therefore, many assumptions and bases of comparison rely on a similar economic analysis study performed by Sabra, Wang & Associates, Inc. included in the previously-referenced report, "MD 28 over Washington Run: Maintenance of Traffic Alternatives Analysis". Additional supporting data has been obtained from MDSHA project engineers and is referenced accordingly.

Construction Time

As shown in Table 1 previously, the typical project duration anticipated for a bridge replacement project of this size is approximately 15 months. Actual construction time required for the MD 28 and MD 450 bridge projects were approximately 4 and 3 months, respectively. One month delay in the MD 28 project was caused by significant underestimation of required pile depth, and otherwise followed the 3 month schedule for planned construction activities. Therefore, the practices and methods used on these projects reduced construction time by nearly a full year.

The most significant impact on construction time reduction is due to operating within a full roadway closure. This allowed the contractor to perform all functions (i.e. material movement and storage, MOT establishment, earthwork, construction) within a single phase of construction and afforded greater freedom to operate by eliminating traffic through the work zone. Additional reductions in construction time were possible through the use of prefabricated bridge elements and incentive contracting, which were attributed to an additional 25% reduction in constructing the superstructure (15 days vs. 20 days for the traditional method).

Construction Costs

Since the contract has not closed, as-built construction costs are not yet available for either project. However, MDSHA has provided comparative construction costs for analysis in a couple of methods. Some of the data used in our economic analysis is based upon estimates originally provided for planning and engineering purposes prior to the establishment of this project as an HfL project, and has been revisited and consulted with MDSHA engineers prior to incorporation in this report.

Table 4 differentiates construction costs for superstructure elements, based solely on the difference between using prefabricated bridge elements (as-built) and using a traditional steel beam bridge (baseline), illustrating a targeted cost savings of $16,000 in superstructure construction costs as a result of utilizing prefabricated superstructure elements.

Table 4 . Comparison of MD 28 bridge superstructure construction costs.

Prestressed Slab Bridge Costs Steel Beam Bridge Costs
Prestressed slabs 264,000 Structural steel 220,000
Superstructure concrete 84,000 Superstructure concrete (8" desk) 115,000
Metal railing 32,000 Superstructure reinforcing steel 24,000
Shear studs 5,000
Metal railing 32,000
Total Superstructure Costs 380,000 396,000
  1. Information in this table presented by MDSHA at HfL Showcase presentation.

The MDSHA Office of Bridge Design provided comparative estimated construction costs for various construction alternatives considered in the MD 28 MOT Alternatives Analysis study. These numbers were used to capture the expected difference in total roadway and structural construction costs based on the number of phases of construction dictated by MOT alternative. Table 5 summarizes these comparative costs between the as-built and baseline MOT alternatives, with the as-built scenario providing an expected cost savings of $310,000 over the baseline scenario.

Table 5 . Comparison of MD 28 structural and roadway construction costs.
MOT Alternative Total Structural & Roadway Cost
Full closure with detour 1,240,000
One lane, two-way traffic (temporary signal) 1,550,000
Notes: Information in this table is referenced directly from "MD 28 over Washington Run: Maintenance of Traffic Alternative Analysis", Sabra, Wang & Associates, Inc., dated April 2007.

It is assumed that the combined effect of cost savings for both utilizing prefabricated bridge elements and constructing the bridge within a full roadway closure will result in a total cost savings of roadway and bridge construction of approximately $326,000.

User Costs

The MD 28 MOT Alternatives Analysis study included a detailed economic analysis section, with calculations and comparative analysis performed to quantify delay, fuel consumption, and safety costs as user costs. This analysis was conducted on behalf of MDSHA and submitted for consideration, based upon valid assumptions and analysis inputs (i.e. accident rates, unit costs) deemed appropriate for the State of Maryland. Therefore, the user costs determined by Sabra, Wang & Associates have been reviewed, summarized, and included in our analysis as follows.

Delay and Fuel Costs

Total delay and fuel costs for the traveling public were determined for the MD 28 project based on the following assumptions:

  • Cost of user delay = $12.10 per hour
  • Cost of fuel = $2.75 per gallon
  • Detour volume per peak hour = 500 vehicles
  • (Peak hour volume / total daily volume) = 8%
  • Average fuel economy = 20 miles per gallon
  • 5 workdays per week

Table 6 summarizes the delay and fuel cost calculations between the as-built and baseline scenarios. As is expected in the case of a full detour, the as-built scenario more than doubles the delay and user costs of the baseline scenario, increasing user costs by $475,650.

Table 6 . Comparison of MD 28 bridge delay and fuel consumption user costs.
Item As-built Baseline
Individual Delay (hours per vehicle) 0.167 0.0167
Individual Delay Cost ($12.10 x individual delay) 2.02 0.20
Peak Hour Delay Cost (500 veh. x ind. delay cost) 1,010 100
Fuel Consumption (7.5 miles / 20 miles per gallon) 0.375 0
Individual Fuel Cost ($2.75 x fuel consumption) 1.03 0.00
Peak Hour Fuel Cost (500 veh. x ind. fuel cost) 515 0
Peak Hour Delay & Fuel Cost 1,525 100
Daily Delay & Fuel Cost (peak hour delay & fuel cost / 8%) 19,063 1,250
Total Days (Project Duration x [5 workdays / 7 days]) 46 321
Total Delay & Fuel Cost (daily delay & fuel cost x total days) 876,900 401,250

Information in this table is based upon data obtained from "MD 28 over Washington Run: Maintenance of Traffic Alternative Analysis", Sabra, Wang & Associates, Inc., dated April 2007. Calculations and rounding for our analysis result in slightly different numbers than those shown in the referenced report.

Safety Costs

In their study, Sabra, Wang & Associates performed a comparative safety analysis between methods, based on a one-mile project length on and adjacent to the MD 28 bridge, considering the various MOT methods and the following analysis inputs based on MDSHA accident data available for a two-lane, two-way, rural non-divided highway:

  • Project length = 1 mile
  • Average daily traffic = 6,000 vehicles per day
  • Average accident cost = $150,000
  • Average fixed-object statewide accident rate = 7.42 per million vehicle miles traveled

The standard rate of accidents for a typical section of highway with no construction work is calculated as:

Rate = (7.42 x 6,000 veh/day x 1 mile x 30 days/month) / 1,000,000 = 1.33 per month.

It was presumed that the presence of a maintained work zone throughout the project site will nearly double the incident rate, resulting in an expected additional one accident per month at a minimum. Therefore, the determined safety cost for the baseline scenario is calculated as:

Baseline cost = (1 accident per month x $150,000 x 15 months) = $2,250,000

In the as-built scenario with a full roadway closure, there will be no accidents within the project limits; however, the increase of detour traffic throughout the immediate area will have an effective increase on accidents, particularly at intersections in the immediate area. Sabra, Wang & Associates reported an expected increase in accident rates, based on MDSHA crash data, of 3 accidents per month for the detour route. Therefore, the determined safety cost for the as-built scenario is calculated as:

As-built cost = (3 accidents per month x $150,000 x 2 months) = $900,000

The expected cost savings in safety user costs from employing the full roadway closure and constructing the bridge utilizing PBES construction methodologies is the cost differential between the baseline and as-built costs calculated above, or $1,350,000.

Cost Summary

Construction costs for the MD 28 project would have likely placed traditional delivery and construction methods (baseline) at $326,000 more than the as-built case. Moreover, utilizing a full roadway closure increase delay and fuel costs by $475,650, but realized in additional cost savings of $1,350,000 in safety user costs. Sabra, Wang & Associates also reported a difference in estimated work zone cost of $426,500 for the baseline scenario and $137,000 for the as-built scenario, resulting in an additional planned cost savings of $289,500.

Therefore, the estimated total savings from using the innovative HfL project delivery approach are approximately $1.49 million for the MD 28 project alone, with a baseline total cost of $4.63 million. It is expected that a detailed analysis with as-built data for the MD 450 project would yield similar results. In other words, the innovative approach to these projects had an approximate 32 percent cost benefit over traditional methods.

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Mary Huie
Highways for LIFE

Updated: 06/22/2011

United States Department of Transportation - Federal Highway Administration