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Bridge Replacements on MD 28 and MD 450, Frederick County and Anne Arundel County, Maryland
Project Overview And Lessons Learned
This project included the quick and efficient construction of two replacement bridges, using innovative techniques, including prefabricated bridge elements and systems (PBES) to provide safer and more durable bridges than those replaced. Precast, prestressed Portland cement concrete (PCC) slabs were fabricated at a plant off-site and shipped to the project sites, allowing rapid construction of critical bridge elements and providing a high quality road surface, as well as a diminished need for bridge maintenance throughout the structure life. In order to minimize both project costs and variability in quality and process, these projects were advertised and awarded in a single contract to one low bidder responsible for building both bridges in a concurrent timeframe.
Each bridge construction was performed within full road closures to minimize inconveniences to commuters and avoid work zone accidents due to traffic-pattern confusion. These closures drastically diminished construction time compared to similar projects constructed within partial roadway closures. The closures took place beginning shortly after the end of the 2007-2008 school year, so as not to impact school bus routes on the project roadways. Prompt completion by the contractor was ensured by incentive/disincentive clauses for schedule performance.
The first bridge carries MD 28 over the Washington Run, near Point of Rocks, Maryland, along the Potomac River in southern Frederick County. The original bridge was 78 years old and rated as "structurally deficient and functionally obsolete". The bridge supported a 25-ft. wide roadway carrying approximately 11,000 vehicles per day.
The second bridge carries MD 450 over Bacon Ridge Branch, west of Annapolis, Maryland in central Anne Arundel County. The original bridge was 82 years old and rated as "structurally deficient and functionally obsolete". The bridge supported a 24-ft. wide roadway carrying approximately 8,000 vehicles per day. The MD 450 bridge was selected as a substitute project for another bridge originally proposed on the HfL grant application as a result of follow-on coordination with the community and resulting concerns by the local fire protection company regarding response times affected by a full roadway closure.
Safety, construction congestion, and quality data were collected prior to and throughout construction to demonstrate that the innovative approaches to this project can be used to achieve the HfL performance goals in these areas. Unfortunately, user satisfaction data was not collected as part of these efforts, as is discussed in a later section.
Safety – Motorist safety is ensured within the work zone by performing full roadway closures for each project. This additionally provided the contractor with greater work area for material storage and equipment operation during all work activities, minimizing the likelihood of work-related accidents on the project site. With no worker injuries reported at either project site, MDSHA exceeded the HfL goal (incident rate less than 4.0 based on the OSHA 300 rate).
It is expected that the long-term performance goal of at least 20% reduction in fatalities and injuries will be easily met, both by the introduction of safer, more durable bridge surfaces to replace those rated as structurally deficient, and by minimizing the need for accessing the bridge for maintenance activities in the future. Furthermore, the increase to the vertical profile for the MD 450 project also eliminated a significant issue with flooding of the east approach roadway of the bridge, thus eliminating significant safety hazards during periods of intense precipitation.
Construction Congestion – Full roadway closures to complete the project construction requires detour routes for each project site to allow an alternative traffic pattern. Alternative traffic pattern studies were performed for each project site by consultants for MDSHA.1 2, Verification of travel times was conducted during construction periods as part of the HfL evaluation of these projects, with travel distances and times recorded and presented within this report.
Increased travel times experienced per vehicle along the detour routes during construction are offset by the significant reduction of maintenance of traffic (MOT) duration and costs associated with a full closure compared to the typical MDSHA activity, maintaining two-way traffic on a single lane roadway using a temporary traffic signal. As reported by MDSHA consultants in the referenced MOT alternative studies, a full closure would typically require an approximate 2-month duration and $15,000 per site for MOT, compared to an approximate 15-month duration and $100,000 per site. Furthermore, as stated previously, the full roadway closure improves both safety and congestion within and adjacent to the project site by eliminating queues and bottlenecks common in a one-lane MOT scenario.
Quality – By using precast PCC slabs, material quality issues and review of elements could happen in advance of using or placing the elements at the project site. The HfL evaluation team for this project visited the precasting plant and observed the fabrication of precast beams for the MD 28 project.
Preconstruction ride quality was measured via two methods: pavement smoothness using IRI and sound intensity using the OBSI technique. Mean values of A-weighted OBSI of 92.9 and 97.6 dB were observed on the preconstruction bridge decks for the MD 28 and MD 450 projects, respectively. Average IRI values of 373 and 406 in/mi were measured on the MD 28 and MD 450 bridge decks prior to construction, respectively.
Due to the short project lengths (and subsequently short analysis and reporting intervals) of these bridges, it was determined that post-construction surveys would not indicate the true magnitude of improvement in surface ride quality. However, by replacing significantly distressed bridge decks and approach pavements and removing expansion joints, both sound intensity and pavement smoothness would be significantly improved by the construction efforts.
The benefits and costs of this innovative project approach were compared with those of a project of similar size and scope with a more traditional delivery approach. MDSHA provided the comparative cost data available to analyze each economic component of the project between the HfL innovative methods and traditional MDSHA practices.
The economic analysis revealed that MDSHA’s approach realized a cost savings of about $1.49 million or 32 percent over conventional construction practices3. A significant amount of the cost savings was from reduced safety costs due to working within a full roadway closure.
Contract Administration proved to be challenging on this project since each project was located in a different Maryland District. Maryland SHA’s construction projects are administered by local district offices. The problem that resulted is that decisions made by one district did not necessarily hold true for the other project in the other district. Because of this, the contractor was required to treat these projects essentially as two independent projects from an administrative stand point and this resulted in some duplication of effort. In addition, SHA’s accounting system is geared to having one and only one district handling a project. Therefore, one of the districts had to handle all financial aspects, which required much communication to understand what was being done in the other district. In the future, SHA might have some meeting prior to construction with the districts involved and assign one district to manage all aspects of both projects. This will allow for consistency and eliminate duplication of efforts.
Ultimately, these projects and the utilization of PBES proved quite successful for MDSHA. Many advantages were realized through the innovations identified within this HfL demonstration project. Several lessons learned from the execution of this contract are summarized herein, including both positive and negative outcomes and considering both the contractor’s and agency’s perspectives.
MDSHA realized many benefits from the use of full roadway closures on these projects. From the MDSHA project engineers’ perspective, this single aspect provided several major benefits alone, including increased safety and decreased construction & curing time for major construction. Looking to the future, and presuming that an economically-feasible detour path is available, Jeff Robert of MDSHA had the following to say regarding full roadway closures:
"Anytime you can construct a project with a detour in place it is a benefit. This creates a safer situation for construction workers and the travelling public and allows the work to be done quicker."
One of the biggest issues concerning successful completion of these projects by the contractor was the drilling and driving of caissons and piles for the abutment construction. On MD 28, the actual required drilling depth was approximately twice the estimated depth from preconstruction soil investigations. This problem, discovered during the roadway closure, delayed the total project schedule by approximately one month for extended drilling. On the MD 450 project, the use of plumb piles did not provide adequate lateral stability during construction and backfill prior to placement of the precast beams.
The MDSHA project engineers gave special consideration to pile placement for this project, and currently some of these lessons have been applied to other projects throughout MD. For instance, a similar project currently under construction is utilizing single lane closures at night to do geotechnical investigation and drilling for caissons and piles in order to minimize the potential for delays and "unforeseen" conditions that would further delay the project.
The MD 450 project illustrated the great care required when utilizing PBES construction methods in forming and placing the elements. It was reported that even after tensioning, the beam did not sit absolutely snug with each other , with total actual width of beam/slab placement expanding by 3 to 4 inches beyond the designed width (sum of beam widths = 43 feet). This had an impact on guardrail alignment.
The use of PBES for this project resulted in great savings of construction time, and MDSHA is currently investigating the use of precast substructure elements to further minimize construction time and traffic impacts. From the contractor’s perspective, however, the three-month total project window has little room for improvement when considering minimum times for earthwork preparation, material testing, and surface placement. MDSHA reports that these projects performed within the HfL program served as effective stepping stones to better, more efficient construction methods.
This project achieved a high level of quality and was brought to completion quickly and safely as a direct result of innovative contracting and construction methods. The success of this project will serve as a vehicle for MDSHA to expand the use of PBES in future bridge projects. Many of the innovations employed were validated as a result of the many experiences gained through this project and have been shown to be valuable tools for future MDSHA projects. Finally, the project also provided MDSHA with valuable experience with administering bundled projects.
1 "MD 28 over Washington Run: Maintenance of Traffic Alternatives Analysis", Sabra, Wang & Associates, Inc., April 2007.
2 "MD 450 over Bacon Ridge Branch: Maintenance of Traffic Alternatives Analysis", Wallace, Montgomery & Associates, LLP, December 2006.
3 These costs were obtained from estimates prepared by MDSHA in planning and comparative analysis of the project alternatives.