|FHWA > HfL > Projects > Maryland Demonstration Project > Data Acquisition And Analysis|
Bridge Replacements on MD 28 and MD 450, Frederick County and Anne Arundel County, Maryland
Data Acquisition And Analysis
Data regarding safety, traffic flow, quality, and user satisfaction before, during, and after construction were collected to determine if this project has 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.
Historical crash data for project limits was not readily available to the MDSHA project engineers at the time of this report for the study projects. However, given that all project work was performed under full roadway closure, the majority of safety concerns are automatically mitigated by enforcing full detours for the traveling public away from the project site.
While there are certain negative effects realized by the implementation of detours (to be discussed heavily in the next section), the detours improved worker and motorist safety during construction. During the construction, no motorist incidents or worker injuries were reported at either site, which means MDSHA exceeded the HfL goals for motorist and worker safety.
Prior to advertisement of the project, MDSHA utilized consultants to perform a study and prepare reports for each project site to analyze potential impact to traffic regarding MOT alternatives, as referenced earlier. Each study considered three MOT alternatives as follows:
Table 1 summarizes typical cost and duration requirements for the various alternatives, considering both the implementation of each MOT alternative and the required phases of project construction relative to a specific MOT alternative, as reported for these projects.
Figures Figure 17 and Figure 18 demonstrate the detour routes utilized during the bridge construction for MD 28 and MD 450 projects, respectively.
Figure 17 . Detour route for MD 28 bridge project.
Figure 18 . Detour route for MD 450 bridge project.
The aforementioned MOT alternative analysis studies considered various inputs and measures from a design and predicted traffic operational standpoint, including intersection capacity analysis, predicted queue lengths and per vehicle delays.
During construction, the HfL project team independently conducted travel time runs to assess the impact of the full roadway closures on motorists for each of the two bridge projects. These studies were conducted during the week of July 7, 2008 in normal daytime traffic patterns. The studies consisted of multiple runs along the designated detour route in each direction, in which incremental travel times were measured for each length of the route. From the measured times obtained, an average and standard deviation of travel time as well as an associated average speed were determined for each detour route. The results for these studies are summarized in Table 2 below.
This project primarily involved the replacement of two bridges that were approximately 80 years old. The most significant measure of improvement of quality for these bridges is the visible improvement in structural adequacy and improved maintainability. The Figures Figure 19 & Figure 20 provide comparative illustrations of the before and after conditions of the MD 28 project.
Figure 19 . Previous condition of MD 28 bridge over Washington Run.
Figure 20 . New condition of replaced MD 28 bridge over Washington Run.
Sound Intensity Testing
Sound intensity (SI) measurements were made using the current accepted on-board sound intensity (OBSI) technique AASHTO TP 76-08, which included dual vertical sound intensity probes and an ASTM Standard Reference Test Tire (SRTT). Sound testing was done prior to construction. A minimum of three runs were made in the right wheelpath of both directions with two phase matched microphone probes simultaneously capturing noise data from the leading and trailing tire/pavement contact areas. Figure 21 shows the dual probe instrumentation and the tread pattern of the SRTT.
Figure 21 . OBSI dual probe system and the SRTT.
The average of the front and rear SI values is computed over the full length of the bridge deck to produce sound intensity 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 are A-weighted to produce the noise-frequency spectra in 1/3 octave bands as shown in Figures Figure 22 and Figure 23 for the MD 28 and MD 450 projects, respectively. On board sound intensity measurements were obtained from the bridges at the posted speed limit of 35 miles per hour (56 kilometers per hour) for the MD 28 project and 45 mph (72 km/h) for the MD 450 project.
Figure 22 . MD 28 mean A-weighted sound intensity one-third octave frequency spectra.
Figure 23 . MD 450 mean A-weighted sound intensity one-third octave frequency spectra.
Global noise levels were calculated by using logarithmic addition of the third octave band frequencies between 315 and 4000 Hz. The onboard preconstruction SI levels for the bridge projects are presented in Table 3 .
Smoothness testing was done in conjunction with noise testing utilizing a high-speed inertial profiler built-in to the noise test vehicle. Figure 24 is an image of the test vehicle showing the profiler positioned in-line with the right rear wheel.
Figure 24 . 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 single IRI value with units of inches per mile. Resulting IRI values of the prerehabilitated bridge and approach pavement are plotted in Figures Figure 25 and Figure 26 at 10-ft (3-m) intervals for the MD 28 and MD 450 bridge projects, respectively.
The average preconstruction IRI value was 373 and 406 inches per mile for the MD 28 and 450 bridge decks respectively (excluding the pavement before and after the bridge). Review of Figure 26 shows large values of IRI in the approach pavements immediately east of the MD 450 bridge and immediately west of the MD 28 bridge. These areas correspond with significant pavement surface distress in the approach pavements.
By nature of removing significant deterioration from the existing paved surface, these construction projects will no doubt improve both the sound intensity and the smoothness of the roadways. However, due to the comparatively short length of these projects, the magnitude of improvement for these measures is not nearly as significant from a user’s perspective as the impact of visual and structural adequacy resulting from bridge replacement. Therefore, it was determined that post-construction testing not be performed on the project.
Figure 25 . MD 28 mean IRI values.
Figure 26 . MD 450 mean IRI values.
As part of the community outreach efforts for these projects and in order to evaluate the effectiveness of these projects in the eyes of the customer, MDSHA presented a two-stage community relations plan to be performed in coordination with the HfL project goals. The first effort was to focus on public meetings and informational project brochures to get the message across to the community prior to execution of the project. This information was designed to obtain public buy-in to the proposed bridge types, traffic/detour management, and project schedule prior to advertisement of the project, while continuing to seek user input throughout planning and construction as well.
Given a relatively short window of construction for these projects, MDSHA planned to execute the second stage, user satisfaction surveys, entirely post construction. These surveys, in coordination with HfL project goals, were to illustrate general user satisfaction via a performance goal of 4+ on the Likert Scale regarding individual satisfaction of the new facility compared to the condition of the old, and individual satisfaction of the project approach by minimizing disruptions. Unfortunately, MDSHA has yet to perform post-construction user satisfaction surveys in conjunction with the project work at either site.
However, both MDSHA project engineers and the MDSHA project coordinator reported a general positive feedback from the community from initial communication and outreach plans through construction to project completion. As an example, Figure 27 illustrates an unsolicited letter received by MDSHA from a local business serving local residents in the area of the MD 450 project.
Figure 27 . Example of positive community response to MD 450 project.