Scope
This project will address the two distinct needs on 12th Avenue through restoration of the collapsed street and new sidewalk construction on the street’s west side. The project will investigate the subsurface void that resulted in the 12th Avenue collapse and return the damaged street to a state of good repair. The project will also reconstruct the existing sidewalk on the west side of 12th Avenue – a portion of which was also damaged in the collapse – to its current endpoint, at the north end of the building at 701 West 135th Street. The project will then construct entirely new sidewalk on the street’s west side, from its current endpoint to 12th Avenue’s intersection with West 138th Street, adjacent to the Riverside Valley Community Garden. Please refer to Attachment 3, Conceptual Drawing, for details.
Secondary Project Scope – Eastern Sidewalk Reconstruction:
Beyond the core scope detailed above, the design consultant should also include reconstruction of 12th Avenue’s eastern sidewalk between West 135th and West 138th Streets in the project’s Schematic Geometric Design (SGD). This sidewalk is currently less than five feet wide at many locations, is in generally poor condition, and ends abruptly 100 feet north of West 135th Street. NYC Parks and the Riverside Park Conservancy have expressed interest in DOT reconstructing this sidewalk in this project, a request DOT would like to accommodate, if possible.
DOT believes the eastern sidewalk scope may be possible to include in this project at the current funding level. The core scope above is currently funded to $5,433,000, which includes approximately $3,300,000 estimated for restoration of the sinkhole outside of 701 West 135th Street, inclusive of soft costs. The sinkhole remediation cost estimate includes a conservative assumption of 2,800 square feet of roadway reconstruction, comprising 12th Avenue’s southbound moving and parking lanes west of NYC Parks’ median Greenstreet. DOT is funding the restoration work to this level to allow DDC to address the wide range of subsurface conditions that could have produced this sinkhole, the exact cause of which is not known at the time of this correspondence.
Given the cost uncertainties associated with sinkhole remediation, and the possibility of surplus funding being available for the eastern sidewalk scope, the design consultant should prepare two final SGD cost estimates – one estimate including only the sinkhole remediation and western sidewalk scope (i.e., the core scope), and a second including the sinkhole remediation, western sidewalk construction, and eastern sidewalk reconstruction (i.e., the core scope + secondary scope). Once the survey, geotechnical investigation, and final SGD cost estimates for both the core and secondary scopes are available, DOT and DDC will determine whether the east sidewalk scope can be included in in the project’s final design and ultimately the capital buildout. This decision point has been included in the project schedule.
Additional Items: City Elements:
The following considerations apply to all aspects of the project area.
Distinctive Materials:
There are no distinctive materials to consider in the project area.
Drainage:
The project should evaluate drainage conditions on the west side of 12th Avenue, near the observed low point in the roadway near 701 West 135th Street. Construction of the west side sidewalk and new curbing is expected to help redirect water in the street toward existing catchbasins and alleviate some of the drainage issues observed at this location. The cost estimate also includes two additional catchbasins, as well as 12-inch ductile chute and related appurtenances, to further address drainage conditions on this block.
Pedestrian Ramps:
The design consultant should verify the ADA compliance of all pedestrian ramps in the project area, and all non-compliant ramps should be upgraded through the capital effort. DOT anticipates 3 pedestrian ramps in the project area will require upgrade. Please refer to the Pedestrian Ramp Inventory attachment for details.
Roadway Markings:
There are currently no markings for bicycle infrastructure within the project limits. This project will introduce new bicycle markings to 12th Avenue, the exact configuration of which will be determined during Schematic Geometric Design, once curb lines have been established for the new sidewalks.
Signage:
Existing signage will be reviewed and all existing and new signage will be consolidated to the greatest extent feasible, including the removal of redundant signs. For any missing regulatory or parking signage, please contact the Manhattan Borough Engineering office.
Signals:
There are no existing signals in the project area, and the project scope does not include the installation of any new signals. Thus, Accessible Pedestrian Signals (APS) are not included in the project scope.
Street Trees:
Tree pits and street trees will be included along the western sidewalk.
