Rapid Removal and Replacement of the 4500 South Bridge over I-215 in Salt Lake City

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.

For this economic analysis, UDOT supplied most of the cost figures for the as-built project. The assumptions for the baseline case costs were determined from discussions with UDOT and FHWA Utah Division staff and national literature.

Construction Time

UDOT believes that, through the use of innovative construction technologies such as SPMTs and ABC, it was able to dramatically reduce the impact of this project's construction on roadway users. For the as-built case, although the substructure and superstructure took several months to complete, the impact on users was minimal until the 4500 South Bridge was ready to be removed and replaced. During this removal and replacement time, full lane closures were in effect on I-215 and SR 266, on which the 4500 South Bridge is located. As discussed earlier, I-215 was impacted for a weekend. However, 4500 South was affected for 10 days after the bridge was put in place while the contractor finished the project.

If a traditional approach had been used to remove and replace the bridge incrementally while maintaining traffic on I-215, UDOT estimates that it would have taken 6 to 9 months to complete the project and that construction-related user impacts would have been felt over a total of 120 days. In this scenario, the median and the inside two passing lanes of I-215 may have been closed to traffic for construction purposes. Periodic closures of the other lanes also may have been necessary.

Detour

As noted earlier, UDOT decided to close I-215 and SR 266 completely during the bridge replacement, which accelerated the removal and replacement process. However, this also required maintaining a detour on local roads. All I-215 traffic was detoured to parallel collector streets and highways. The designated detours did not increase travel time significantly. The 4500 South traffic used the same detour roads.

Construction Costs

Table 1 presents the differences in construction costs between the baseline and the as-built alternatives. All of the as-built cost estimates were provided by the UDOT project engineer assigned to this job. The baseline cost was determined in consultation with the FHWA Utah Division bridge engineering staff by (1) noting whether the itemized costs in the as-built cost table would have applied to the baseline case, (2) making adjustments to cost categories and costs as necessary, and (3) itemizing other costs associated with the baseline case that may not have been required for the as-built case. The baseline cost estimate is inexact, therefore, and the information presented is a subjective analysis of the likely cost differential rather than a rigorous computation of a cost differential. Several other assumptions were made in selecting significant cost factors and determining some unit costs, as noted in Table 1.

User Costs

Generally, three categories of user costs are used in an economic/life-cycle cost analysis: vehicle operational costs (VOC), delay costs, and crash and safety-related costs. The cost differential in delay costs was included in this analysis to identify the differences in costs between the baseline and as-built alternatives. Because the anticipated period of user impact during the bridge replacement was relatively short (120 days for traditional versus about 2 days for accelerated) and the site under consideration is in an area with relatively low crashes, it was decided not to compute crash costs. Also, the short detour lengths precluded computation of VOC.

Because SR 266 essentially becomes a local road west of I-215 (toward the Wasatch Mountains), the impact of delay costs on users of SR 266 is not considered significant compared to I-215 below. However, for the sake of completeness, the user delay costs for SR 266 have also been compiled and noted in the following paragraphs.

The following baseline information was available for I-215:

• Based on the data provided by UDOT, the ADT on I-215 was 64,000.
• User impact analysis performed by UDOT on the peak 2 hours of north- and southbound traffic resulted in the following conclusions:
  • Average delay: 11.7 minutes per vehicle
  • Maximum delay: 25.9 minutes per vehicle
  • Average queue length: 2.11 mi (3.39 km)
  • Maximum queue length: 4.8 mi (7.72 km)
• It was assumed that 15 percent of all I-215 traffic would be diverted to detour roads if traditional traffic maintenance techniques were used. However, UDOT decided to not include the delay on detours in the cost analysis.
• UDOT estimates that the delay costs amounted to $31,000 a day. These costs were based on delay costs of $12 an hour per private vehicle and $28 an hour per commercial truck.

The following baseline information was available for SR-266:

• Based on the data provided by UDOT, the ADT on SR-266 is 14,800.
• Most of the residents are expected to take a detour with minimum impact in travel time.
• UDOT estimates that the delay costs amounted to $3,000/day (or about $0.25 per day per vehicle).

Assuming that traditional construction would have impacted traffic for about 120 days and using the average estimated delay cost of $34,000 a day, the additional delay costs for the baseline case would have been $4,080,000 ($34,000/day * 120 days). Based on the user impacts on SR-266 and assuming a total of 10 days of disruption to traffic (2 days for the bridge removal and replacement plus 8 days for approach slab construction and other miscellaneous work to be completed until SR-266 was open to traffic), the delay costs accrued for the as-built case were $30,000 ($3,000/day * 10 days). Several factors ensured that these costs were minimal, including the following:

• The bridge removal and replacement was performed over a weekend. Weekend traffic typically is lower than weekday traffic.
• UDOT’s extensive efforts to keep the public informed about the full lane closure on I-215 and SR 266 over the weekend when construction took place resulted in lower traffic levels and congestion.
• The designated detours were sufficient to handle the traffic that had to pass through the affected zone and, based on anecdotal evidence, did not cause excessive queuing.

Cost Summary

From a construction cost standpoint, traditional construction methods would have cost UDOT about $806,504 ($9,721,504 - $8,915,000 from table 1) less than accelerated construction. However, the ABC techniques saved $4,050,000 ($4,080,000 - $30,000) in user costs. Therefore, the net savings on this project totaled $3,243,496 ($4,050,000 - $806,504). Using the estimated total costs for designing and constructing the bridge with traditional practices as a basis, the innovative HfL project delivery approach realized a cost savings of about 36 percent. Moreover, UDOT has noted a downward trend in first costs as ABC use has increased and contractors have become more comfortable with the techniques that embody this project delivery approach. As gathered from recent bridge construction activity in Utah, this trend has provided a greater incentive for increased use of ABC contracting in Utah.