Much has been said how Interstate 70 is a physical barrier between downtown and the Arch grounds—a moat that is crossable in only a few select locations. Less has been said about the psychological barrier the highway presents, particularly when it comes to noise pollution. After a quick visit to the Arch, I can conclude that not construction of a one-block lid over I-70 nor the removal of large segments of Memorial Dr will noticeably reduce noise pollution at the JNEM.
Using my iPhone (assuming it is accurate), I measured noise levels during the morning rush at various points along I-70 within and near the Arch grounds.
As a point of comparison, I first measured the noise levels of a nearby downtown street, Broadway between Chestnut and Pine. When traffic was passing by, my iPhone recorded an average of 73 decibels; without traffic, a relatively peaceful 61 decibels.
On the Arch grounds, the quietest spots I measured were behind the Old Cathedral and at the base of the east side of the berm separating the Arch from the highway. Noise levels averaged 58 decibels in these locations. Slightly noisier was the center of Luther Ely Smith Park at 63 decibels.
Between Walnut and Pine in line with the middle of the Old Cathedral, I consistently measured noise levels averaging about 67 decibels. This measurement was remarkably consistent over time even during the frequent lulls in traffic passing by on Memorial Dr.
To verify that Memorial Dr was an insignificant contributor to noise levels in the vicinity of the highway, I went a little farther north to where Interstate 70 is level and at-grade with the surrounding terrain directly. At this location, my iPhone revealed the obvious roar of the highway reading 75 decibels with occasional 2-3 decibel spikes from passing trucks. Twenty feet up from the balcony of the “ground floor” of the Mansion House, the highway droned even louder at 77 decibels.
For reference, MoDOT considers the installation of soundwalls whenever noise levels exceed 65 decibels.