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

Data Acquisition and Analysis

Data collection on the UDOT HfL project consisted of acquiring and comparing data on safety, construction congestion, quality, and user satisfaction before, during, and after construction. The primary objective of acquiring these types of data was to provide HfL with sufficient performance information to support the feasibility of the proposed innovations and to demonstrate that ABC technologies can be used to do the following:

  • Achieve a safer work environment for the traveling public and workers.
  • Reduce construction time and minimize traffic interruptions.
  • Produce greater user satisfaction.

This section discusses how well the UDOT project met the specific HfL performance goals related to these areas.

Safety

The HfL performance goals for safety include meeting both worker and motorist safety goals during construction. During the construction of the 4500 South Bridge project, no worker injuries or motorist incidents were reported, which means UDOT exceeded the HfL goal for worker safety (incident rate of less than 4.0 based on the OSHA 300 rate).

A 0.38-mi (0.61-km) segment of I-215 was selected for the operational safety reporting before construction. This roadway segment included the 4500 South Bridge on SR 266 and part of the pavement on either side of the structure. The 3-year crash histories (2003 $8211;2005) for I-215 and SR 266 in the vicinity of the 4500 South Bridge provided by UDOT are below. According to UDOT, none of the crashes can be attributed directly to the structure that was replaced:

  • Sixty-one crashes on I-215 (primarily rear-end collisions with no fatalities)
    • Thirty-two crashes along the main line (52.5 percent).
    • Twenty-nine crashes on the ramps (47.5 percent).
    • None of the crashes were fatal and there was only one incapacitating injury reported within this period.
  • Nine crashes on SR 266 (primarily rear-end collisions)

Between the time the HfL project was completed and the date of this report, no motorist crashes were reported, so the goal of reduced motorist crash rates was achieved in the short term. This measure will be tracked for several years.

Construction Congestion

The HfL program specifies performance goals for reducing both total construction duration by 50 percent and construction impacts on traffic. Under conventional methods, the construction impact on both roads was estimated at 40 to 50 weeks. With the use of ABC techniques, the impact was reduced to a weekend for I-215 and 10 days for SR 266. There was minor impact on I-215 for 8 weeks during the construction of the CIP spread footing (foundation for the abutments), abutments, and wingwalls. Jersey barriers were used to separate the shoulders from the outside travel lanes, allowing the contractor to use the shoulder for these construction tasks. I-215 experienced somewhat slower traffic because of the 8-week shoulder elimination. During the removal and replacement of the 4500 South Bridge, I-215 was closed to all traffic for 48 hours. In essence, the major impact on I-215 was for only a weekend.

Both the reduction in total construction time and in impacts on motorists compared to conventional construction methods for this project far exceeded the HfL performance goals.

Quality

Sound Intensity Testing

Sound intensity (SI) measurements were taken on October 22, 2007, before reconstruction, at the posted speed limit of 30 miles per hour (mi/h) (48.2 kilometers per hour (km/h)) using the latest industry standard onboard sound intensity (OBSI) technique. This method employs dual vertical sound intensity probes and an ASTM F 2493 standard reference test tire (SRTT). Figure 28 shows the dual probe instrumentation and the tread pattern of the SRTT.

OBSI dual probe system and the SRTT.

Figure 28. OBSI dual probe system and the SRTT.

Sound measurements were recorded using an onboard computer with the Brüel and Kjær PULSE software and data collection system. A minimum of three test runs were made in the right wheelpath of the inside lane in each direction. The dual sound intensity probes simultaneously collect noise data from the leading and trailing tire-pavement contact areas, and the PULSE software uses Fourier transform to analyze the raw data signals over the full length of each test run to produce SI values.

The values are normalized for environmental effects such as ambient air temperature and barometric pressure at the time of testing. The resulting A-weighted mean SI levels are filtered to produce the noise-frequency spectra in one-third octave bands, as shown in Figure 29.

Mean A-weighted sound intensity one-third octave frequency spectra.

Figure 29. Mean A-weighted sound intensity one-third octave frequency spectra.

The onboard preconstruction SI levels on the 4500 South Bridge in each direction of travel were as follows:

  • Eastbound SI = 94.5 dB(A)
  • Westbound SI = 95.6 dB(A)

The average preconstruction SI level was 95.1 dB(A), determined using the measurements from the test runs in both directions and logarithmic addition of one-third octave band frequencies between 315 and 4,000 hertz (Hz).

On December 5, 2007, the postconstruction pavement/tire SI levels were acquired at 30 mi/h (48.2 km/h). At this time, the precast superstructure had not been overlaid with the final riding surface. The onboard postconstruction SI levels on the 4500 South Bridge in each direction of travel were as follows:

  • Eastbound SI = 94.8 dB(A)
  • Westbound SI = 95.7 dB(A)

The average postconstruction SI level determined as described above was 95.3 dB(A).

These data suggest the difference between pre- and postconstruction SI levels was not significant. Both pre- and postconstruction SI levels were excellent and slightly exceeded the HfL target values.

Smoothness Measurement

Smoothness testing was done in conjunction with SI testing using an inertial laser profiler manufactured by International Cybernetics Corp. and built into the noise test vehicle. Figure 30 shows the test vehicle with the laser positioned in line with the right rear wheel.

Laser profiler mounted behind the test vehicle.

Figure 30. Laser profiler mounted
behind the test vehicle.

At least three test runs were conducted in each wheelpath in each direction and were averaged to produce a singe IRI value with units of inches per mile. Resulting IRI values of the prerehabilitated bridge and approach pavement are plotted in Figure 31 at 10-ft (3-m) intervals.

The average preconstruction IRI value was 223 inches per mile for the existing bridge deck (excluding the pavement before and after the bridge). Figure 31 shows large peak values near the ends of the bridge resulting from rough expansion joints.

Postconstruction smoothness testing performed on December 5, 2007, showed that the IRI value on the precast deck was higher than the preconstruction values at 265 inches per mile. The final riding surface was not placed on this bridge before postconstruction IRI data collection. Although the thin riding surface is not expected to decrease the IRI dramatically, it is expected to provide a better match between the pre- and postconstruction test results.

Nevertheless, the HfL goal for IRI of 48 inches per mile, which reasonably can be met on long, open stretches of pavement, was not met on this project. It is extremely difficult to achieve this mean ride measurement on a short-span bridge of this type because of the influence of the bumps at each end of the structure on the mean.

Mean IRI values.

Figure 31. Mean IRI values.

User Satisfaction

During the planning and construction of the 4500 South Bridge, UDOT implemented an aggressive, comprehensive communication effort with residents and businesses in the affected zones to keep them informed of all activities. The public information manager (PIM), a private contractor hired by UDOT, was charged with providing information and facilitating communication among the public, the construction contractor, the UDOT resident engineer and the UDOT Region 2 public involvement coordinator (PIC).

The PIM developed and implemented a comprehensive public involvement plan that included an extensive mailing and contact lists. The PIM facilitated an open house-style public hearing and personally met with the neighboring residents and businesses along the corridor to gather comments, receive feedback, and address concerns. Through fliers, newsletters, e-mails, and a dedicated hotline, the public was kept aware of key project schedules and milestones on a weekly or as-needed basis. The PIM also submitted a detailed report on construction updates at each weekly meeting. In addition, the PIM was responsible for preparing a project summary page on the UDOT Web site that included project background, information about upcoming construction activities, and a schedule of key events. The summary page was updated periodically to reflect the project's progress. The HfL requirement for user satisfaction included a performance goal of 4-plus on a Likert scale of 1–7 for the following two questions:

  • How satisfied are you with the results of the new bridge compared to the condition of the previous bridge?
  • How satisfied are you with the approach UDOT used (accelerated bridge construction) to construct the new bridge in terms of minimizing disruption?

A postconstruction stakeholder survey conducted by UDOT indicated that neighboring residents and businesses were extremely satisfied with the construction approach and the final product. UDOT far exceeded the HfL goal of 4-plus on the Likert scale. Figure 32 illustrates UDOT's and the contractor's overall performance during the project and Figure 33 shows stakeholders' overall satisfaction with the project results. For complete results of UDOT's user satisfaction survey, see Appendix A.

UDOT and contractor overall performance.

Figure 32. UDOT and contractor overall performance.

Stakeholders' overall satisfaction.

Figure 33. Stakeholders' overall satisfaction.

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Mary Huie
Highways for LIFE
202-366-3039
mary.huie@dot.gov

This page last modified on 04/04/11
 

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