U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Data collection on the ADOT 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. It was also done to demonstrate that an innovative sequencing process and carefully staged construction coupled with the use of prefabricated bridge components and performance-based incentive/disincentive clauses (lane rental) can be used to accomplish the following:
This section discusses how well the ADOT project met the specific HfL performance goals in these areas.
The HfL performance goals for safety include meeting both worker and motorist safety goals during construction. For ADOT, safety of the workers and the traveling public was job number one and began before the construction commenced. All site personnel, field crews, designers, inspectors, and owner’s representatives received site-specific orientation and safety training before working on this project. ADOT’s outreach through the NBIP process created a safer and quicker construction schedule with the least amount of interference with traffic flow and the least amount of disturbance to the businesses, surrounding roadway, and right-of-way.
During the reconstruction of the SR 179 roadway, a few worker injuries were reported, but they were minor. Six incidents were reported over a 2-year period (i.e., 0.25 incidents per month). None of these injuries resulted in loss of work for the workers. Overall, the contractor exceeded the HfL goal for worker safety (incident rate of less than 4.0 based on the OSHA 300 rate).
The safety of the traveling public was of concern. ADOT’s foremost solution was to minimize traffic disruption and interaction with construction activities and workers. The crash history for the 5-year period between May 1, 1998, and April 30, 2003, showed a total of 245 crashes, 134 of which were rear-end crashes. The crash breakdown was as follows: 77 percent noninjury, 11 percent possible injury, 9 percent nonincapacitating, 1 percent incapacitating, zero fatal, and 2 percent unknown.
During construction, the contractors took extraordinary steps to assure that crashes were kept to a minimum. The many safeguards ADOT put in place to prevent incidents during construction were effective. These included implementation of an innovative pilot program to train local law enforcement personnel on enforcing laws in and around the project construction zone. ADOT also hired additional law enforcement officers (doubling the number of officers) for their visible presence throughout the project. Other effective measures included open houses, regular news releases, a dedicated phone line, and a Web site.
ADOT Traffic Records Group gathered crash data during and after construction. Table 1 presents the crash statistics by KABCO scale (a measure of the functional injury level of the victim at the crash scene) collected before, during, and after construction. As indicated in the table, the crash frequencies during construction for all crash types except injury possible (C) type were almost the same as before construction.
|Crash Type||Preconstruction||During construction||Postconstruction|
|Injury evident (B)||22||12||1|
|Injury possible (C)||27||4||0|
|Property damage only (O)||189||101||8|
|Date (Days) of Coverage||5/1/1998 to 4/30/2003 (1,826)||2/11/2008 to 9/27/2010 (960)||9/28/2010 to 12/31/2010 (95)|
Expedited construction is a key HfL performance goal that specifies a 50 percent reduction in the time highway users are impacted during construction compared to traditional practices. ADOT believes that through innovative construction sequencing of the six roundabouts (building half of the roundabout at a time), carefully staged construction of the Oak Creek Bridge, and the use incentive/disincentive contract clauses (lane rental), it was able to dramatically reduce the impact of construction activities on neighboring residents, businesses, tourists, and roadway users.
To assess the impact of the construction project on motorists, researchers used the floating vehicle methodology to collect travel times, attempting to mimic the typical driving speed of other vehicles along the various roadway segments of the detour route. Data were collected in April 2008 during daytime hours because traffic demands were lower at night and any effects of the total roadway closure would be smaller. Specifically, data were collected in the a.m. peak (7 to 9 a.m.), noon (11 a.m. to 1 p.m.), and p.m. peak (4 to 6 p.m.) periods. Because of significant tourist traffic on this facility, data were collected on weekdays (Thursday and Friday) and on weekends (Saturday and Sunday). The project was already underway when data were first collected, so no preconstruction data could be obtained. However, researchers used a previously-prepared traffic report to estimate preconstruction travel times.
Figure 27 illustrates the limits of the project. Travel times were obtained between Back O’ Beyond Road to the south and the SR 179/SR 89A intersection to the north.
Figure 27. Limits of travel time study.
|Time Period||Northbound Travel Time (minutes)||Southbound Travel Time (minutes)|
Travel times in each direction were averaged across four to six runs in each of the six time periods (weekday a.m., noon, and p.m. and weekend a.m., noon, and p.m.). These average travel times are shown in table 2.
Average travel times ranged from 7.4 to 16.4 minutes northbound and from 7.0 to 9.5 minutes southbound. These correspond to average speeds between 30 miles per hour (mi/h), the approximate posted speed limit on the roadway, and 13 mi/h. Weekday travel times tended to be greater than those on the weekend, despite expectations that weekend traffic conditions would be worse because of higher tourist traffic volumes on Saturday and Sunday. Data collection staff noted indicate that weekday noon and p.m. travel times were occasionally delayed by flagging operations. However, a review of the travel time data indicated that such delays were limited to 30 seconds or less.
The biggest influence on northbound travel times did appear to be the traffic signal at the SR 179/SR 89A intersection. The northbound direction at the signal gradually became oversaturated and resulted in lengthy queues in the weekday noon and p.m. time periods. However, this type of backup did not occur on the weekends, so it is possible that weekday construction activities at the north end of the project had some confounding effects on the signal.
Delay Analysis Results
The lack of preconstruction data created a challenge in determining what impacts the project had on motorist delays. A 2004 traffic study suggested that the intersection signal at SR 179/SR 89A generated an average of 20 seconds of additional delay per vehicle during the Saturday p.m. peak period. However, the report did not provide additional insights on total corridor travel times that existed before construction. The report's age also made it difficult to draw solid inferences on travel time impacts of the project.
The general traffic-handling scheme used for the project would be expected to cause only minimal additional traffic delays because the number of lanes that existed before construction was maintained during construction. However, interactions between work activities at the north end of the project and the operation of the traffic signal may have caused some additional delay during weekdays (based on the extent of low-speed operations observed on weekdays at the north end of the project). As a conservative estimate, it is suggested that the average weekend travel times be used as a baseline of conditions that existed before construction and that the difference between weekday and weekend travel times be attributed to work activities occurring throughout the project. Table 3 summarizes those delay numbers.
|Time Period||Northbound Delays (minutes per vehicle)||Southbound Delays (minutes per vehicle)|
Pavement Test Site
Sound intensity (SI) and smoothness test data were collected from three 525-ft tangent sections avoiding roundabouts, curves, and hills on SR 179 through Sedona. These three test sections serve as a representative sample of the highway. 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 was collected before construction and on the new pavement surface after the road was opened to traffic. SI measurements were recorded and analyzed using an onboard computer and data collection system. Multiple runs were made in the right wheel path with the two microphone probes simultaneously capturing noise data from the leading and trailing tire-pavement contact areas. Figure 28 shows the dual probe instrumentation and the tread pattern of the SRTT.
Figure 28. OBSI dual probe system and the SRTT.
The average of the front and rear SI values was computed to produce a global SI value from the three test sections. Raw noise data were normalized for the ambient air temperature and barometric pressure at the time of testing. The resulting mean SI levels were A-weighted to produce the frequency spectra in one-third octave bands, as shown in figure 29.
Figure 29. Mean A-weighted SI frequency spectra from before and after construction.
SI levels were calculated using logarithmic addition of the one-third octave band frequencies across the spectra. The global SI value was 94.9 dB(A) for the existing pavement and 91.8 dB(A) for the new pavement. The SI levels from the new construction meets the HfL goal of less than 96.0 dB(A) and is a noticeable 3.1 dB(A) quieter than the old pavement.
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 wheel paths and averaged to produce an IRI value. Low values are an indication of higher ride quality (i.e., smoother road). Figure 30 shows the test vehicle with the profiler positioned in line with the right rear wheel. Figure 31 graphically presents the IRI values for the preconstruction and newly constructed pavement. Shaded areas on the plot indicate the test sections (IRI values are plotted continuously for the new pavement as a reference). The existing distressed pavement had a 209 in/mi value and the new pavement had a 135 in/mi value. While not meeting the HfL goal of less than 48 in/mi, the 135 in/mi is much smoother than the existing pavement.
Figure 30. High-speed inertial profiler mounted behind the test vehicle.
Figure 31. Mean IRI values for the bridges and roadway before construction.
As indicated earlier, during the planning stages of the project ADOT began an aggressive and comprehensive effort to communicate with affected residents and businesses along the SR 179 corridor and keep them abreast of all pre- and postconstruction activities. The HfL requirement for user satisfaction included a performance goal of 4-plus on the Likert scale of 1-7 for the six questions listed in Appendix.
Although the project went over the expected construction contract duration by 8 to 9 months, the result was well received by the community. ADOT's postconstruction stakeholder survey clearly indicated that neighboring residents and businesses were satisfied with the construction approach and the final product. ADOT exceeded the HfL expectation by a large margin.