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Highways for LIFE

Arrow Rhode Island Demonstration Project: Replacement of Frenchtown Brook Bridge No. 435

Economic Analysis

A key aspect of HfL demonstration projects is quantifying, as much as possible, the value of the innovations deployed. This involves 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.

For this economic analysis, RIDOT supplied the cost figures for the as-built project and baseline construction. Traditional methods would have involved the use of cast-in-place construction coupled with standard pretensioned precast concrete bridge beams.

Construction Time

The baseline scenario would have closed the bridge for at least 6 months to accommodate traditional cast-in-place construction methods. The ABC approach allowed the contractor to fabricate the bridge components ahead of time and use a condensed 33-day closure to assemble the bridge.

Construction Costs

The alternative analysis for the Frenchtown Brook bridge project itemized costs for six options, with the following three lowest cost options:

  1. Precast arch option ($1,800,000)
  2. Butted box beam option ($1,840,000 without piles, $2,160,000 if piling needed)
  3. Spread box beam option ($1,880,000 without piles, $2,190,000 if piling needed)

Details of the analysis are shown in Table 1.

The precast arch option was estimated to cost $40,000 less than the conventional alternative of butted box beam and $360,000 less if piling was needed for the butted box beam structure.

The successful (lowest) bid on the project was $1,945,063.80.

Assuming that the conventional bridge would have been bid proportionately higher, the difference between the conventional option and the precast arch option is estimated as follows:

$1,945063.80 * 40,000/1,800,000 = $43,223.64 or about $43,000.

However, with the incentive of $90,000 for completing the project ahead of the time allotted, the innovative option cost $47,000 more than the conventional option.

Table 1. Construction cost analysis.
Table 1. Construction cost analysis.

User Costs

Generally, three categories of user costs are used in an economic and life cycle cost analysis: vehicle operating costs (VOC), delay costs, and crash- and safety-related costs. Because the bridge would have been closed to traffic under both the baseline and as-built cases, the possible safety hazard to the traveling public from a work zone was eliminated, so safety-related costs were not evaluated. However, VOC and delay costs were compared and are discussed in the following subsections.

VOC

The savings in VOC from using ABC are essentially the difference between the mileage-related VOC applied to the 6 months (183 days) of detour time for the baseline case and the 33 days for the as-built case applied to an average extra detour distance of 2 mi.

Assuming an average unit cost of $0.81 per mile for commercial vehicles (light and heavy trucks)² and $0.32 per mile for an average sedan³ for the variable operating costs (including costs for fuel, maintenance and repair, tires, and depreciation) and given the 2012 annual average daily traffic (AADT) of 7,300 with 6 percent trucks for this project, the following VOC is computed:

Baseline Case

VOC(Auto) = 7,300(AADT) * 0.94(percent autos) * 2(mi) * $0.32(per mi) * 183 (days) = $803,677

VOCTruck = 7,300(AADT) * 0.06(percent trucks) * 2(mi) * $0.81(per mi) * 183(days) = $129,849

VOC(Total) = $803,677 + $129,849 = $933,527

As-Built Case

The detour was in effect for 33 days, hence the VOC (total) for the as-built case is as follows:

= 33 * 933,527/183 = $168,341

VOCDifferential= $933,527baseline – $168,341As-built = $765,186

Delay Costs

The delay time using the primary and alternate detour routes averaged 2.67 minutes (0.0445 hour) and 1.40 minutes (0.0233 hour), respectively, more than travel before closure. RIDOT estimated that traffic would be distributed about 50 percent on each detour route. The average delay time is calculated as follows:

Delay time per vehicle = 0.5 * 0.0445 hour + 0.5 * 0.0233 hour = 0.0339 hour

The savings in delay cost can be determined by applying an hourly value to the extra time needed to traverse the detour and assuming a monetary hourly value of $19.68 and $23.57 an hour for autos and trucks, respectively4:

Baseline Case

Delay(Auto) = 7,300(AADT) * 0.94(percent autos) * 0.0339(hr/veh) * $19.68 (per hr) * 183 (days) = $837,773

Delay(Truck) = 7,300(AADT) * 0.06(percent trucks) * 0.0339(hr/veh) * $23.57(per hr) * 183(days) = $64,045

Delay(Total) = $837,773 + $64,045 = $901,818

As-Built Case

Delay(Auto) = 7,300(AADT) * 0.94(percent autos) * 0.0339(hr/veh) * $19.68(per hr) * 33(days) = $151,074

Delay(Truck) = 7,300(AADT) * 0.06(percent trucks) * 0.0339(hr/veh) * $23.57(per hr) * 33(days) = $11,549

Delay(Total) = $151,074 + $11,549 = $162,623

The total saving in delay costs between baseline and as-built scenarios is as follows:

DelayDifferential= $901,818Baseline$162,623As-built = $739,195

Cost Summary

From a construction cost standpoint, the innovative ABC delivery approach cost RIDOT about $43,000 less than traditional construction. However, with $90,000 in incentive for early completion, the construction cost for the ABC delivery approach ended up costing $47,000 more.

User costs, however, were substantially lower for the ABC delivery approach. Compared to the conventional (baseline) approach, VOC costs were $765,186 lower and delay costs were also lower by $739,195 (see Table 2).

In summary, in terms of total costs, the conventional (baseline) approach would have cost 3,823,409 or about 62 percent more than the cost of $2,366,028 for the innovative ABC delivery method implemented on this project.

This project saved users $1,457,381 or about 38 percent of the total project costs for conventional construction.

Table 2. Comparison of project costs.
Item Innovative Method Conventional Method Difference
Construction Cost $1,945,064 $1,988,064 $ 43,000
Vehicle Operating Cost (VOC) $ 168,341 $ 933,527 $ 765,186
Delay Cost $ 162,623 $ 901,818 $ 739,195
Incentive $ 90,000 0 $ (90,000)
Total $2,366,028 $3,823,409 $1,457,381


²Barnes and Langworthy, The Per-Mile Costs of Operating Automobiles and Trucks, 2003, Report No. MN/RC 2003-19, Minnesota Department of Transportation. Adjusted for fuel price increase and inflation in 2011.

³American Automobile Association, Your Driving Costs 2012, Both operating costs and per mile depreciation costs were considered. http://newsroom.aaa.com/wp-content/uploads/2012/04/YourDrivingCosts2012.pdf

4Mallela and Sadasivam, Work Zone Road User Costs and Applications, Report No. FHWA-HOP-12-005, Federal Highway Administration, 2011. Per hour travel delay cost for autos was adjusted for Rhode Island’s 2011 median annual household income of $49,033.

Updated: 05/29/2013

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