HMMH's noise analysis for the I-395 HOV Ramp EA followed the new 2011 FHWA regulations under 23CFR772 and the new VDOT Highway Noise Guidance Manual. The study area included much high-density residential development and an extensive botanical garden. Up to 635 dwelling units were identified as potentially impacted by noise in the 2035 Build case. Noise abatement with barriers was evaluated and found to be feasible and reasonable for all impacted residential and recreational areas. The total length of the barriers would be approximately 6,150 feet, the heights would range from 15 to 30 feet, and they would cost approximately $4.3 million. The barriers would provide sufficient noise reduction benefit to 150 impacted residential and recreational units, and they would benefit another 333 units.
An air quality project level analysis was conducted for carbon monoxide (CO), particulate matter (PM) and Mobile Source Air Toxics (MSATs) from potential traffic impacts associated with the proposed I-396 HOV Ramp. A hot spot analysis for CO was required as expected traffic volumes will exceed the qualitative analysis threshold criteria and was conducted consistent with the VDOT Consulting Guide and EPA/FHWA guidance using the latest versions of MOBILE6.2 and CAL3QHC. A qualitative analysis was performed for PM2.5 emissions since the Project is located in a non-attainment area for PM2.5. A qualitative MSAT analysis was also conducted since the Project was considered to have low potential MSAT effects per FHWA NEPA guidance criteria.