Category: Greenbelt Station

The Greenbelt Station developer has sent the study report below on reflected noise from the Greenbelt Station development. The College Park City Council was considering to ask the developer to conduct the noise reflection study at tonight’s Council meeting. Please let me know if you’ve any questions.

Figure below shows an aerial photo of the site. The aerial photo shows the two Metrorail tracks (closer to the Greenbelt Station site), the two CSX railroad tracks (farther from the Greenbelt site), some new roads built on the Greenbelt Station site, and neighboring houses across the railroad in the Hollywood neighborhood.

The approximate locations of the proposed noise wall and three evaluation points labeled A, B, and C are also marked in Figure 1. It can be seen that there are many houses in the Hollywood community to the northwest including those on Huron Street and Iroquois Street. The land
immediately to the west of the Greenbelt Station site is an undeveloped forest bounded by 51st Avenue and Huron Street, with an industrial area further south. We have assumed that the only concern of this analysis is the residential community, and not the forest or industrial area. Locations A, B, and C as labeled in Figure 1 represent the houses on 51st Avenue and Huron Street that are closest to the Greenbelt Station site, as well as a house somewhat farther away.
Previously, we measured sound levels on the Greenbelt Station site in two locations for nearly four days.

Sound levels were extrapolated to other locations on the Greenbelt Station site based on the assumption that sound levels vary solely as a function of distance from the railroad. Based on the predicted noise levels, a noise wall has been proposed to mitigate railroad noise reaching the Greenbelt Station townhouses.

It was determined for freight trains sound levels dropped off at a rate of approximately 6 dB per doubling of distance with the acoustical centerline fairly close to the near edge of the near pair
of CSX tracks, while for Metro trains sound levels dropped off at a rate of approximately 4.5 dB per doubling of distance with the acoustical centerline roughly between the two pairs of Metro tracks. We used this same approach to estimate the Day-Night Average Sound Level (DNL) at locations A, B, and C in Figure. The resulting predictions are that the DNL are 74.6 dB, 66.9 dB, and 74.9 dB at locations A, B, and C, respectively. These sound levels are quite high.

In order to estimate whether the proposed noise wall would amplify railroad noise at locations A, B, and C we used the computer program SPM9613. The SPM9613 algorithms are based on the ISO standards 9613 Parts 1 (1993) and 2 (1996) which consider geometric divergence of sound, attenuation of sound by the atmosphere, and interaction of sound with the ground. The input to the noise model included:
• Three dimensional coordinates of the railroads. The CSX railroad and Metrorail tracks were
each modeled as a series of noise sources located along the centerlines between the pairs of
tracks. The sound power levels were arbitrarily set to 100 dB in all frequency bands; since the
focus is a change in noise level, the absolute sound power levels are not that important. The
source height was 0 up to 15 feet above the tracks.
• Three dimensional coordinates of the top and bottom of the proposed noise wall. It was
conservatively assumed that 100% of the sound hitting the noise wall bounces off (i.e., it has a
reflection coefficient of 1.0).
• Three dimensional coordinates of points A, B, and C, with a nominal height of 5 feet above the
ground, and a medium-hardness ground near them and midway to the railroad.

The resulting prediction is that the noise wall would only increase sound levels 0.1 dB at locations A and B, and 0.0 dB at location C. A change of 3 dB would be just barely perceptible. A change of 0.1 dB is completely imperceptible. In other words, there will be no noticeable reflections and noise levels will not increase noticeably due to the noise wall.

There are two reasons why reflections off the noise wall will not be significant. First, and most
importantly, the noise wall height is not that great relative to the horizontal distance between the noise wall and houses. Second, the noise wall does not extend as far north as the Hollywood houses. If the wall extended past the storm water management pond, the increase in noise level would be somewhat higher.

At tonight’s Council meeting, the City Council will discuss and vote on the the Southcore development’s detailed site plan.

At the November 17, 2015 worksession meeting, the Council discussed the Detailed Site Plan (DSP) for Phase III of the Greenbelt Station South Core development. At their regular meeting, November 24, 2015, the Mayor and Council moved to table the request until tonight’s worksession meeting in order for staff to meet with City of Greenbelt staff to obtain comments on a practical location for a pedestrian overpass.

The applicant is in the process of revising their DSP submittal based on comments they received from the City of Greenbelt, the City of College Park and Maryland-National Capital Park and Planning Commission staff. The Technical Staff report will not be completed until the revised DSP has been submitted and referrals have been distributed.

The Prince George’s County Planning Board hearing, previously scheduled for January 7, 2016, is tentatively scheduled for February 4, 2016. The Greenbelt City Council is anticipated to take a position on January 11 , 2016. They would like to receive input from the City regarding the pedestrian overpass.

The project is located entirely within the City of Greenbelt and is subject to a Development Agreement between Greenbelt and the Developer. As a result, City staffs review and comments are limited to those issues that directly impact the City of College Park. The main concerns are the location of a pedestrian bridge crossing over the WMA T A/CSX rail corridor and noise impacts from a required noise wall.

City of College Park staff met with City of Greenbelt staff on December 4th to discuss acceptable locations for the pedestrian overpass based on plan revisions made by the Applicant.

Toole Design was requested to propose additional options focused on connecting to new green space provided in the revised plan. On December 28, College Park and Greenbelt staff met to discuss Toole Design’s revised report (Attachment 1). It was determined that Alignment below was the preferred alternative because it best complied with the District Council condition, had the least impact on residents of the Daniels Park neighborhood, and had the least impact on Greenbelt Station residents.

City staff recommends approval ofDetailed Site Plan 13045, the South Core of Greenbelt Station, Phase III with the following conditions:
1. Prior to final plat certification, the applicant shall create a lot that is a minimum of 175feet long by 50-feet wide, shown as Alignment 2A in the City of College Park Pedestrian Overpass Feasibility Study Additional Concept Alternatives, Addendum to the Technical Summary. This lot shall be held by the Homeowners’ Association to be turned over to a public agency on demand for construction of a public pedestrian overpass. After 10 years from the date of final plat certification, if a pedestrian overpass has not been constructed, the lot will become the property of the Homeowners’ Association.
2. Prior to certificate approval of the Detailed Site Plan, the applicant shall revise the site plan to relocate the pedestrian overpass to the area shown as Alignment 2A in the City of College Park Pedestrian Overpass Feasibility Study Additional Concept Alternatives, Addendum to the Technical Summary.
3. Prior to certificate approval of the Detailed Site Plan, the applicant shall provide a determination from a certified sound engineer that indicates whether exterior reflective noise from the proposed sound wall will have a perceptible impact to residences on Huron Street from the railroad tracks to 51 51 A venue and to residences on 51st A venue from Blackfoot Place to Huron Street. If there is such an impact, the applicant shall revise the DSP to show a sound wall with an absorptive material or coating in order to mitigate reflective noise. a. The absorptive material or coating shall have a Noise Reduction Coefficient (NRC) of 0. 70 or greater. b. The absorptive material or coating shall be used for the entirety of the west side of the sound wall facing the railroad tracks.
4. Prior to certificate approval of the Detailed Site Plan, the applicant shall provide the City of College Park with broker information and promotional material for the retail site.
5. Subsequent to the determination that Lot 116 is to be retail or a public park and prior to the issuance of a building permit for Lot 116, the applicant shall provide a Detailed Site Plan revision to address site layout and building details.