The economic argument for transit system vibration mitigation

This “economic argument for action” is excerpted from a presentation that we developed about light rail vibration impacts on university labs. Similar thinking has also been applied broadly to “energetic contaminants” like EMI / magnetic fields and others. If you're interested in hearing more, don’t hesitate to contact us.

The economic argument for vibration mitigation

All new transit projects require some degree of environmental impact assessment, but some of the most intense scrutiny surrounds noise and vibration. The most-challenging problems involve mass transit rail near high-tech and laboratory uses, like at university science departments or National Labs. These can be extraordinarily sensitive, far beyond anything that would be annoying to people.

Even concert halls and hospitals are far less impacted than research labs, for which energetic contaminants like vibration, noise, and EMI / magnetic fields can be devastating. Unlike other sensitive uses — where human sensibilities govern — these high-tech uses tend to become more sensitive over time. There is nothing about classical music that makes the concert halls of today more sensitive than those of the past. However, any scientist/technologist doing physical research will tell you that their field has evolved significantly, even during their own careers.

This means that impacts to institutional campuses from new sources of environmental vibrations (like light rail systems) can affect not only existing research but can also place fundamental limits on the kinds of research that can be conducted there in the future. This is unique to “technical” sensitivities, and means that it is worth thinking deeply about protecting high-quality research environments.

Highly-Sensitive, but also High-Value

It seems easy to dismiss the concerns of scientists and engineers who use these labs, especially when it becomes obvious that environmental mitigations might cost millions of dollars for a large rail project. On a simple economic basis, however, these sensitive research and development uses cannot be disregarded. These institutions rely directly on quiet environments for noise, vibration, and EMI / magnetic field fluctuations, and while the costs of preservation may seem large, they are dwarfed by the value of the work that is done on campus.

A large university might have annual research grant budgets in the billions of dollars. We recently conducted an informal survey of departmental grant summaries published by the Office of Sponsored Programs at a large American university. The school had been involved in extensive negotiations regarding transit system (LRT) impacts to campus via vibration, EMI, and acoustical noise. The 2019 annual report documents almost $200M in annual grant activity solely within the hard sciences and engineering, along with another $174M between an environmental sciences program and a standalone applied physics lab.

Add in another $800M+ in grants at the associated medical research center, and it is clear that fantastic sums of money – and hundreds or even thousands of jobs – are on the table.

Research in those departments is driven by physical experimentation, and a significant fraction of this work is highly sensitive to interference from vibration and magnetic field fluctuations, including those generated by passing trains. Between the science/engineering departments and the medical research functions in this university example, it is conceivable that something on the order of $100M in funding could depend directly or indirectly upon suitably quiet lab environments.

These are extraordinary – and annually-recurring – sums that should signal the economic importance of these activities in society. In this light, the millions of dollars in rail vibration mitigation seem like less of a pure cost and more of an investment, and at the very least could be thought of as cheap insurance.

Vibration Impacts at the Institutional scale

Notably, impacts from transit systems affect entire organizations and departments: many of the objections that we have heard as vibration consultants center around competitiveness in funding acquisition (poor research productivity leads to smaller grants) as well as competitiveness in attracting and retaining top faculty. The administrators of departments like Chemistry and Physics are very clear that the availability of quiet lab vibration environments is critical to the success of the entire department, and university leaders do not hesitate to point out the importance of science and technology to the schools’ missions. In exclusively research-oriented environments like corporate R&D campuses and at National Laboratories, the connection between quiet vibration environments and institutional success is even more direct.

Preserving these vibration-sensitive laboratory spaces is therefore highly valued. Just as receiver-based mitigation is unattractive, so too is relocation. Due to unique utility, space-management, and hazardous materials needs, laboratory spaces are not trivial to implement in routine commercial buildings and usually require purpose-built structures. Even in cases where relocation is superficially economical due to scale (there are enough vibration-affected labs to warrant the construction of an entire building), research program managers are justifiably concerned about physically separating users in the department, or separating them from their colleagues in other departments. Indeed, the architectural trend in lab design has been toward buildings that foster interaction between different research groups, even (perhaps especially) across disciplines: just look at the number of new university facilities for which the word “interdisciplinary” appears in the building name.

Quiet vibration environments as economic policy

These R&D campuses are centers of economic activity not only in the immediate sense but also in the broader sense that these are the places where tomorrow’s technologies are born. Given the economic stakes involved, from both the direct (grants) as well as indirect (regional / national competitiveness) perspectives, it should be clear that unnecessarily damaging this kind of economic engine is poor policy.

These institutions usually support new transit projects. Given the human populations of these campuses, better transportation is strongly desired. Indeed, any large university should crave better and smarter transportation options to help ease pressures on campus traffic (itself a source of vibration impacts), parking, and housing. Good policy means finding ways to economically introduce mass transit access for the campus and surrounding communities without damaging or limiting the research functions at the core of the institutional mission.

It's not impossible; rather, it just requires thinking about – and advocating financing for – investments in rail vibration and EMI / magnetic field mitigation strategies. When you consider just how much economic activity is at stake, it should be easy to justify the relatively small (and mostly one-time) costs to maintain an institution’s ability to generate world-class research.

Contact us if you need help negotiating around environmental vibration impacts to sensitive buildings at your campus. We have experience with infrastructure impacts, especially from new light rail and other transportation systems. We can help keep your campus quiet and productive, even as transportation options are improved for everyone.

Environmental vs local sources of building vibration

We previously wrote about receiver-based vibration isolation systems – isolation pads or platforms that sit right below electron microscopes and other sensitive nanoscale imaging tools. In that discussion, we pointed out that these systems are more effective at reducing micro-vibration at higher frequencies than at lower frequencies. In fact, a major component of the vendors’ marketing materials is to demonstrate good low-frequency performance, often by citing a system resonance or "isolation frequency". Just like machine vibration isolators, lower is better.

This is important because many common imaging tools are more sensitive at lower frequencies. What’s more, floor vibrations in labs aren’t uniform across the spectrum: there might be more or less low-frequency content to begin with. But what governs how much energy we see at different frequencies in the spectrum?

Here’s an example micro-vibration spectrum. These statistics are based on data taken across the footprint of an aging university laboratory. Obviously, there is a lot more high-frequency than low-frequency vibration. While not shown here, the narrowband (high-resolution) data indicated that building machinery vibrations dominate at high frequencies. Based on the data, this site meets the “VC-C” criterion of 500 micro-inches/sec (12.5 micro-meters/sec); however, it could perform far better if mechanical system vibrations were addressed.

This “mix” of energy content in the spectrum isn’t completely random: different kinds of sources contribute to or even dominate different parts of the spectrum. The first and most obvious distinction between different "kinds of sources" is local vs. environmental.

Local vibration sources are those things in and around the building itself: machinery, foot traffic, structural/foundation systems, the parking lot. Environmental sources are those things external to the building: roads, transit lines, rail corridors, even the “seismicity” of the regional geology.

Here’s another example micro-vibration spectrum. These statistics are based on data taken at a proposed site for a university imaging center that would house vibration-sensitive electron microscopes. As you can see, there is a lot of energy down at around 2Hz. Based on the data, this site meets the “VC-D” criterion of 250 micro-inches/sec (6.3 micro-meters/sec). There's not much you could do to improve this site, since the spectrum is dominated by ground vibrations arriving from outside the building. 

What is interesting about this differentiation is the degree of control that might be exerted over those sources. The owner of a vibration-sensitive laboratory building has far more control over local sources than environmental sources. During design and construction, the owner and design team can aggressively isolate new or existing building machinery or lay out the project so as to increase local distances between sensitive labs and vibration sources. But the owner typically has little or no control over environmental sources: traffic from city-owned streets or nearby rail systems might dominate, and nobody can do much to improve the regional geotechnical condition or alter the soil dynamics that determine long-range ground vibration propagation.

It’s true that a large entity like a university or a national lab will sometimes be able to influence the local authorities that operate and maintain nearby roadways or transit lines. Additionally, on large campuses the owner’s own roads might be relevant. These are important special cases, and the owner should use its resources and position to demand maintenance schedules or alignments that minimize the ground vibration impacts from these sorts of sources. But in general, you can think of environmental sources as things that are practically beyond anyone’s (straightforward) control.

It turns out that there is an important rule-of-thumb when it comes to micro-vibration frequency content from these two kinds of sources. In general, environmental sources tend to dominate at low frequencies, while local sources are often more important at higher frequencies. This is all down to physics: low frequencies travel farther in soil, so we don’t often see a lot of high-frequency ground vibration from far away; meanwhile, machinery vibrations are strongest at the RPMs of the shaft speeds, so building machinery creates the greatest vibrations mid- and upper-spectrum frequencies near 15Hz (900RPM), 30Hz (1800RPM), 60Hz (3600RPM), etc.

A decent rule-of-thumb for building vibration, including low-vibration labs and other engineered settings: environmental sources like traffic and nearby rail lines tend to dominate at low frequencies, while local sources like building machinery tend to control at high frequencies. Obviously, there are exceptions, but this is a reasonable starting point when trying to decide if a site can be made to work for sensitive uses like electron microscopy. 

This distinction is important because environmentally-driven building vibration is very difficult to mitigate against. So it’s important to be able to understand where those floor vibrations are coming from, and whether you have much ability to do something about them – other than moving to a low-vibration lab space at a remote location.

Upcoming paper: statistical descriptors in the use of vibration critiera

If you are a member of IEST and have some interest in low-vibration environments in research settings, I will encourage you to sit in on a session on "Nanotechnology Case Studies" at ESTECH. I'll be presenting some work on the statistical methodologies that we have been developing over time. I know of at least three other presentations, and they all look intriguing. So, I hope that this will be well-attended. See the abstract for my paper below.

"Nanotechnology Case Studies", ESTECH 2017, May 10 from 8AM to 10AM

Consideration of Statistical Descriptors in the Application of Vibration Criteria

Byron Davis, Vibrasure

Abstract:

Vibration is a significant “energy contaminant” in many manufacturing and research settings, and considerable effort has been put into developing generic and tool-specific criteria. It is important that data be developed and interpreted in a way that is consistent with these criteria. However, the criteria do not usually include much discussion of timescale or an appropriate statistical metric to use in determining compliance. Therefore, this dimension in interpretation is often neglected.

This leads to confusion, since two objectively different environments might superficially appear to meet the same criterion. Worse, this can lead to mis-design or mis-estimation of risk. For example, a tool vendor might publish a tighter-than-necessary criterion simply because an “averaging-oriented” dataset masks the influence of transients that are the actual source of interference. On the other hand, unnecessary risk may be encountered due to lack of information regarding low- (but not zero-) probability conditions or failure to appreciate the timescales of sensitivities. 

In this presentation, we explore some of the ways that important temporal components to vibration environments might be captured and evaluated. We propose a framework for data collection and interpretation with respect to vibration criteria. The goal is to provide a language to facilitate deeper and more-meaningful discussions amongst practitioners, users, and toolmakers.