|FHWA > HfL > Projects > Utah Demonstration Project: Precast Concrete Pavement System on I-215 > Data Acquisition and Analysis|
Utah Demonstration Project: Precast Concrete Pavement System on I-215
Data Acquisition and Analysis
Data on traffic flow and quality 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 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:
Construction Congestion and Travel Time
No actual travel time studies were performed during this project. Instead, UDOT has a transportation management system on major routes throughout Salt Lake City and its suburbs. Consequently, spot speed and flow data during the project dates were available along the study section at about 0.5-mi spacing. Detailed (5-minute average) speed data aggregated across all travel lanes for the majority of sensor locations within the project section were extracted from UDOT’s performance measurement system. Any significant drop in speeds at a sensor location was then extrapolated over a freeway section representative of that sensor to estimate delay over the segment, and delays over multiple segments were totaled to provide an overall estimate of traveler delay.
Hourly traffic flow data at a representative sensor location in the project segment were also extracted to assess the possible delays that would have occurred had a more traditional slab replacement approach (such as cast-in-place full-depth repairs) been used. Such an approach would involve the long-term closure of one or two lanes over multiple days to allow removal of existing concrete, placement of reinforcing bars and concrete, curing, and installation of pavement markings.
UDOT project personnel anticipated that the use of nighttime lane closures would minimize traffic disruptions, and staff comments after the project was completed suggested that those expectations were met. A review of spot speeds each night at several sensor locations verified that the project itself had little, if any, impact on traffic. As indicated in Figures 33 through 37, speeds at each sensor location throughout each night were at or near free-flow speeds (60 to 70 miles per hour). Thus, the project generated no significant delays within the project limits on any of the nights it was active.
Figure 33. Average speeds southbound at sensor station 105, milepost 26.8.
Figure 34. Average speeds southbound at sensor station 108, milepost 25.8.
Figure 35. Average speeds southbound at sensor station 112, milepost 24.4.
Figure 36. Average speeds southbound at sensor station 115, milepost 23.5.
Figure 37. Average speeds southbound at sensor station 119, milepost 22.8.
The use of precast concrete panels allowed work to be completed as a series of short-term nighttime lane closures. If this technology had not been used, a more traditional rehabilitation scheme would have been required, typically a long-term closure of one or two lanes over several days. For comparison purposes, Figure 38 illustrates the typical hourly flow rates on I-215 on weekdays and highlights what capacity would have been if this traditional method of slab replacement had been used. Note that a single long-term lane closure on this section would have resulted in overcapacity conditions each weekday morning from about 6 until 8 or 9. If two lanes would have been closed on a long-term basis, oversaturation would have existed during most of the daytime hours, leading to long delays and queues. This latter point is illustrated in Figure 39, which shows average per-vehicle delay that would have resulted daily from long-term lane closures.
Further analysis of these data provides a summary of the total vehicle-hours of delay per day expected had the traditional method of slab replacement been used, shown in Table 2. The two-lane values are slightly conservative because the delays at midnight in Figure 39 would have had to dissipate in the early morning hours before the a.m. peak and contributed to the delay total. With these numbers, it is possible to estimate the total delay costs avoided by estimating the total number of days it would have taken to replace the slabs via traditional methods and multiplying that estimate by these daily delay values and a unit value of delay time per vehicle.
Figure 38. Hourly volumes southbound on I-215, weekdays.
Figure 39. Average per-vehicle delays that would have resulted from long-term lane closures on I-215.
Pavement Test Site
Sound intensity (SI) and smoothness test data were analyzed from a 300-ft tangent section of the project pavement. Comparing these data before and after construction provides a measure of the quality of the finished pavement.
Sound Intensity Testing
SI measurements were made using the current accepted OBSI technique AASHTO TP 76-10, which includes dual vertical SI probes and an ASTM recommended standard reference test tire (SRTT). Data were collected before construction on May 7, 2010, and on the new pavement surface on August 9, 2011, after it was opened to traffic. The SI measurements were recorded and analyzed using an onboard computer and data collection system. Multiple runs were made in the right wheelpath with two microphone probes simultaneously capturing noise data from the leading and trailing tire-pavement contact areas.
Figure 40. shows the dual-probe instrumentation and the tread pattern of the SRTT.
The average of the front and rear SI values was computed to produce a global SI value. Raw noise data were normalized for the ambient air temperature and barometric pressure at the time of testing. The resulting mean SI levels are A-weighted to produce the SI frequency spectra in one-third octave bands, as shown in Figure 41.
Figure 41. Mean A-weighted sound intensity frequency spectra before and after construction.
Figure 41 . Mean A-weighted sound intensity frequency spectra before and after construction.
Smoothness testing was done in conjunction with SI testing using a high-speed inertial profiler integrated with the test vehicle. The smoothness or profile data were collected from both wheelpaths and averaged to produce an IRI value. Low values are an indication of higher ride quality (i.e., smoother road). Figure 42 shows the test vehicle with the profiler positioned in line with the right rear wheel. Figure 43 graphically presents the IRI values for the preconstruction and newly constructed pavement. The existing distressed pavement had a value of 150 in/mi, and the new pavement was 130 in/mi. Motorists may notice a somewhat smoother ride, but the rehabilitated pavement did not meet the HfL goal of 48 in/mi.
Figure 42. High-speed inertial profiler mounted behind the test vehicle.
Figure 43. Mean IRI values before and after construction.
The HfL requirement for user satisfaction includes a performance goal of 4-plus on a Likert scale of 1 to 7 (in other words, 57 percent or more participants showing favorable response) for the following two questions:
Overall, the response to the questions exceeded the HfL goal of 4 out of 7 (the majority of the respondents) or more showing favorable response.