Longest running on Broadway?

Paving Article January 22, 2008
Printer-friendly version

Serving a vibrant mix of cars, buses, delivery trucks and pedestrians, Broadway is one of downtown Denver’s most significant arterials. Adjacent to the landmark Brown Palace Hotel and just north of Civic Center Park, the four-block segment of Broadway from 16th to 20th avenues links many of downtown’s major destinations and is a primary route for downtown traffic circulation.

Frequent maintenance of Broadway’s asphalt surface was an ongoing maintenance challenge, with continual maintenance operations impeding traffic on Broadway and heavy daily traffic creating a hazardous environment for maintenance crews. The pavement was rutted from heavy traffic and settling of the pavement and curb and gutter created drainage problems along the entire length of the street. Rebuilding the street was a necessity, and in 2005 the city and county of Denver secured federal funds for the planning, design and construction for the complete reconstruction of Broadway.

Under the direction of the city and county of Denver Capital Projects Management Department, the Denver office of URS Corp. was retained to complete the planning and design of the project. The challenges of this street reconstruction project were significant: Traffic would need to be maintained at all times along Broadway; myriad decades-old utility lines would need to be protected or replaced concurrently with the street paving; street drainage improvements were needed; Denver’s noise ordinances would limit the contractor’s work to daylight hours; continuous access to major downtown parking lots and garages would need to be maintained; pedestrian access and safety would be of utmost importance in this bustling commercial district; and full environmental clearances would need to be obtained from the Colorado Department of Transportation.

 

Show plays to heavy crowds

Geotechnical subconsultant Geocal Inc. prepared a pavement selection report that considered general traffic and heavy vehicle demand, initial capital costs and life-cycle maintenance costs, and concluded that concrete pavement would be the most cost-effective choice for the reconstruction of Broadway. But concrete paving of a busy downtown arterial introduced a host of new challenges.

Minimizing impact to downtown commuters, visitors and residents was critical. A public workshop and one-on-one meetings with city traffic and planning staff, adjacent landowners, parking operators, office building managers and the downtown’s business organization—the Downtown Denver Partnership—confirmed that an aggressive construction schedule would have the least disruption on corridor operations. Information gained about weekday and weekend building and parking operations was used in the development of the project’s phasing plan.

Maintaining traffic with an aggressive construction schedule was a key challenge. Heavy traffic demand throughout the day, a light-rail line crossing and complicated five-point intersections along the length of the corridor eliminated the option of major closures for lane and intersection reconstruction because of the unacceptable traffic congestion and delay these closures would create. Working with the city’s team from Capital Projects Management and Traffic Engineering Services, URS prepared a complex phasing plan that was based on the complete reconstruction of all of the major corridor intersections on the weekends.

To limit disruption to the traveling public, construction generally progressed on a block-by-block basis, with demolition work staying about a block ahead of the paving activities. Utility relocation and adjustment began immediately following the removal of the old pavement.

High early-strength concrete was specified for all weekend construction work, allowing concrete to be poured and gain sufficient strength to allow its use for the Monday morning commute. For this corridor, selection of the right construction materials was a key to a high-quality surface that met the aggressive schedule requirements.

The required field compressive strength was 4,200 psi at 28 days. Lanes were allowed to be open to traffic after the pavement reached 2,500 psi, which took seven days or less. The high early-strength concrete reached a field strength of 2,500 psi within 24 hours. Concrete cyclinders were cast and tested to confirm the required strength was achieved prior to opening lanes to traffic.

Sequencing of the remaining concrete work also was designed to meet the requirement for the use of a multilane slipform paver for improved surface quality. The sequencing plan was carefully devised to allow the longitudinal pavement joints to coincide with the lane lines. The slipform paver placed 11½-in.-thick concrete for 10½-ft-wide lanes. The high early-strength concrete, which was used for all intersection work, was also 11½ in. thick.

Utility lines in the corridor were identified from surface evidence and a records search. Each utility company was contacted to review the project limits and construction schedule and to identify any concurrent work to maintain or replace any of the exposed utility lines in the corridor.

 

Tracking history

The design team worked closely with the Colorado Department of Transportation to obtain the required environmental clearances for the project. A unique feature of the corridor was a network of shallow streetcar tracks, long buried beneath Broadway, which needed to be removed to allow for the placement of concrete pavement. In addition to creating a photo record of the tracks as they were exposed during excavation and removal, the project team developed a permanent interpretative display sign that was erected near the Brown Palace Hotel. “The Birth of Denver Mass Transit” traces the city’s history of mass transit from the early streetcars to the current light-rail transit system.

The project also relocated the Beaumont Fountain, a part of the city’s public art collection, to a more visible and prominent location. The fountain restoration and relocation allowed for a number of significant improvements to the fountain basin structure and electrical/mechanical systems to improve their operation and decrease the maintenance requirements.

 

In between festivals

As construction neared, the city determined that all the work requiring lane closures must be accomplished by the contractor in the three-month window between two major downtown festivals—June’s Capitol Hill People’s Fair and Labor Day’s Festival of Mountain and Plain. Castle Rock Construction Co. was selected by the city for the construction contract.

Senior staff from Castle Rock Construction worked with city staff and the consultant team to refine the project phasing to meet the aggressive schedule. Updated phasing plans to reflect proposed weekend construction limits and the sequence of weekday lane closures were prepared.

Weekend work was critical to meeting the project schedule. Commuters leaving downtown on Friday were greeted with newly reconstructed intersections on Monday morning. City project managers and inspectors along with materials testing crews worked weekend shifts to monitor construction and test pavement strength prior to opening completed sections to traffic. Weather was an issue during construction, and special care was given to placing and monitoring the high early-strength concrete during the summer’s record heat.

Initially, the concrete delivered to the project site was rejected because it was over 90°. The supplier identified that the problem was caused by the aggregate sitting in the sun and becoming hot enough to raise the temperature of the concrete mix. An evaporative cooler was used to reduce the temperature of the aggregate before mixing it into the concrete. The concrete was then delivered within the correct temperature tolerance because of the short haul distance. The contractor also was able to receive the concrete and place it before the sun could heat it up again.

Regular broadcast e-mails kept corridor stakeholders informed of the progress of construction. Construction progressed at a vigorous pace, meeting the city’s three-month schedule with no adverse media coverage and few stakeholder complaints.

This segment of Broadway also was selected as Denver’s test case for the use of “countdown” pedestrian signal heads. The corridor’s office towers generate significant peak-hour and noon pedestrian volumes. Grant funding acquired late in the construction process allowed for the implementation of these innovative traffic-control devices, which are designed to improve pedestrian safety.

 

Gold in Colorado

In addition to recognition of the project by the Colorado Chapter of the American Public Works Association, the reconstruction of Broadway received a national Gold Award (Municipal Streets and Intersections) from the American Concrete Pavement Association. The project also won a Merit Award from the American Council of Engineering Companies (ACEC) of Colorado.

With another successful project, the city and county of Denver continue to challenge conventional thinking about constructing concrete pavement in heavily traveled arterial corridors. The reconstruction of Broadway demonstrates that with proper planning and execution, busy downtown corridors can be reconstructed in concrete with minimal disruption to the community.

About the author: 
Schaefer is a project manager for URS Corp., Denver, and Ohlrogge is a project manager for the city and county of Denver Public Works Department.
Overlay Init