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North Dakota Demonstration Project: Whitetopping on U.S. 2 West of Rugby
Data Acquisition And Analysis
Data on safety, traffic flow, quality, and user satisfaction before, during, and after construction were collected to determine if this project met the HfL performance goals. The primary objective of acquiring these types of data was to quantify the project performance and provide an objective basis from which to determine the feasibility of the project innovations and to demonstrate that the innovations can be used to do the following:
Achieve a safer work environment for the traveling public and workers.
The crash data from the original pavement (see below) shows that one injury crash and no fatal crashes occurred within the project limits during the 3-year study period. This is not a significant numbers of crashes. However, to help keep injury and fatal crashes to minimum, NDDOT, as previously mentioned, upgraded the roadway to enhance safety by flattening shoulder slopes, installing turn lanes, and eliminating dangerous wheelpath rutting.
Existing Crash Data
Nature of Crash
At the completion of construction, no incidents involving motorists or construction workers were reported. Worker safety was greatly increased by eliminating live traffic from the work zone with full lane closure. Also, the detour speed limit was lowered to minimize the possibility and severity of crashes.
The full lane closure allowed the contractor to relocate the westbound traffic to an eastbound lane, completely separating the paving operations from live traffic. By doing so, eliminated the need to slow traffic to 40 mph (64 km/h) through the work zone and then drastically reducing the speed limit to 25 mph (40 km/h) around the immediate work area as would be required for traditional construction.
During construction the speed limit was reduced from 70 mi/h (112.7 km/h) to 60 mi/hr (96.6 km/h) for the eastbound head-to-head traffic lanes. Reducing the speed limit caused trip time to increase from 6.9 minutes to 8.0 minutes. Even though the trip time was increased, traffic flowed freely and no noticeable backups were reported. As a result, queue lengths for vehicles approaching and traveling through the detour were nonexistent.
Sound Intensity Testing
NDDOT had not used the onboard sound intensity (OBSI) test method on any past projects. However, this method was used to collect tire-pavement sound intensity (SI) on the existing and newly rehabilitated pavement on the U.S. 2 project. OBSI measurements were obtained at highway speed.
Sound intensity measurements were made using the current OBSI technique AASHTO TP 76-08, which uses dual vertical sound intensity probes and an ASTM-recommended standard reference test tire (SRTT). The sound measurements were recorded and analyzed using an onboard computer and data collection system. A minimum of three runs were made in the right wheelpath of the project. The two microphone probes simultaneously captured noise data from the leading and trailing tire-pavement contact areas. Figure 9 shows the dual probe instrumentation and the tread pattern of the SRTT.
Figure 9 . OBSI dual probe system and the SRTT.
The average of the front and rear SI values was computed to produce SI values. Raw noise data were normalized for the ambient air temperature and barometric pressure at the time of testing. The resulting mean sound intensity levels were A-weighted to produce the noise-frequency spectra in one-third octave bands, shown in figure 10.
Figure 10 . Mean A-weighted sound intensity frequency spectra.
Sound levels were calculated by using logarithmic addition of the one-third octave band frequencies between 315 and 4,000 hertz (Hz). The sound level was 102.8 for the original distressed HMA pavement and 103.9 for the newly completed whitetopping pavement. Newly constructed longitudinally tined concrete pavements typically have an SI ranging from 102.0 to 105.0 dB(A), depending on the type of pretexture used in combination with the tining 1. Although the HfL goal of 96.0 dB(A) was not met, the sound level of the new pavement is reasonable.
The project did not include the HfL goal for IRI of less than 48 inches per mile. However, like most States, NDDOT has other specifications for testing the surface tolerance and ride quality of concrete pavements. Section 550.04.P of NDDOT's Standard Specifications for Road and Bridge Construction (2002) is summarized below:
The contractor did not have any unexpected issues achieving the NDDOT contract smoothness specifications outlined above. Smoothness testing required by the HfL goal and following the ASTM E 950 method was done in conjunction with noise testing using a high-speed inertial profiler built in to the noise test vehicle. Figure 11 shows the test vehicle with the profiler positioned in line with the right rear wheel.
Figure 11 . High-speed inertial profiler mounted behind the test vehicle.
Figure 12 graphically shows the test results taken on a 1-mi section of the original distressed HMA pavement on the west end of the project. Construction activities restricted testing to the west end of the project, but the section is nonetheless representative of the entire project. Testing was conducted on nearly the full length of the newly constructed whitetopped pavement. The graph shows a spike in the new pavement's IRI values near the east end of the project because of a small dip in the road. Otherwise, the IRI values are relatively consistent along the project. The original pavement values are much more variable, largely because of the cumulative effects of patches, rutting, and transverse cracking.
Figure 12 . Mean IRI values for the old and new pavements.
Smoothness testing shows a 64 percent drop in postconstruction IRI value. Preconstruction IRI was 199 inches per mile for the existing HMA pavement, while postconstruction IRI was only 71 inches per mile. The new pavement does not meet the HfL target value of 48 inches per mile, but is still a substantial improvement over the original pavement.
The HfL requirement for user satisfaction is a performance goal of 4-plus on a Likert scale of 1 to 7 for the following two questions:
1 Hall, J.W., Smith, K.L., Littleton, P., Texturing of Concrete Pavements (NCHRP Report 634), National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, 2009.