Noise

May 23, 2016 wpopp No comments exist

Version 1, 23 May 2016

dreamstime_m_47668457_thumbIt is important to note that any form of grade separation is likely to reduce some of the existing rail noise as the need for boom gate bells, some train braking and some mandatory train horns are eliminated or reduced by the grade separation.

Since all options would provide the same savings from these kinds of rail noises, most of the discussion below is in relation to other rail noise across the various options (eg. the vibrations of the carriages, the tracks, the freight trains’ engines, etc.).

We’ll discuss the following below:

  1. Current Government Noise Policy compliance
  2. Overview of Elevated Bridge Noise and Below Ground Bridge Noise
  3. The LXRA Preliminary Noise report for the Dandenong line
  4. Our Response To Noise Impacts

1. Does Government Policy Protect Us?… Maybe

The Good News

Engineering_VicGov_Rail_Noise_Policy_ThumbA grade separation will mean changes to the existing rail infrastructure and would require compliance with the Passenger Rail Infrastructure Noise Policy (State of Victoria 2013). (This is a separate issue to Construction Noise, which operates under the usual EPA rules).

The Passenger Rail Infrastructure Noise Policy (State of Victoria 2013) is available here.

The policy comes into effect if noise levels following the project’s completion is predicted to exceed:
– 65dB(A) during the day (6am-10pm), or
– 60dB(A) at night (10pm-6am), or
– A maximum level of 85dB(A) (at any time).

I wonder why the policy calls “Passenger Rail”, what about the freight trains???

For reference: 60dB is the noise of a conversation, 70dB is approximately the noise of a shower or dishwasher and 85dB is approximately the noise of a passing diesel truck. Hopefully, no one has that noise level in their homes from rail now!

The Bad News

Sadly, this policy only requires that the authorities consider options to avoid, minimize and mitigate. They don’t have to actually do anything!. To quote from page 6 of the policy (underlines are ours):

If an assessment shows that the investigation thresholds will be exceeded, noise impacts should be considered a primary matter. This means that transport bodies and planning authorities should consider options for avoiding, minimising and mitigating rail noise by applying the policy principles set out in Attachment 3 as a set. Transport bodies and planning authorities may find that there are no appropriate options in some cases.

Transport bodies and planning authorities should seek the views of the Minister for Public Transport and the Minister for Planning.

In accordance with section 21 of the Transport Integration Act 2010, transport bodies and planning authorities should consider publishing a report demonstrating how the principles have been applied. (Page 6, Passenger Rail Infrastructure Noise Policy, State of Victoria 2013). 

So, when the LXRA says that they will comply fully with the noise criteria, you can be sure they are meeting it – you just can’t be sure whether all additional noise will be fully mitigated or whether they will “consider” and conclude that there are no appropriate options for that case.  The policy gives them that “wriggle room” while still allowing “full compliance”.

2A. Elevated Rail Bridge Noise

Anyone who has ever stood near an existing rail bridge in use (near the Melbourne Aquarium for instance) can attest that it is certainly no quieter than the current at-grade rail we already experience.

But currently, with the at-grade tracks, the houses immediately on each side of the tracks are the most impacted by noise, as the noise is partially filtered to the houses further back by other houses and vegetation.  This is slightly less obvious where roads occur.  The State government policy noted above mentions this on Page 15 of “Considerations for applying policy principles”: “Shielding provided by other buildings”.

Say NO To Sky Rail (Skyrail) - Frankston Line - Engineering - Noise Effects
Refer also: LXRA CD9 Preliminary Noise Report: Figure 3 – Environmental Noise Propagation

Assuming that the elevated rail bridge produces the same rail noises (as the carriages move over the rails, vibrations etc,), and without additional noise mitigations, the noise from an elevated rail bridge would be noticeably increased for those houses not currently experiencing the full impact.

Say NO To Sky Rail (Skyrail) - Frankston Line - Engineering - Noise Effects

Based on our conversations with LXRA, each one of the grade separations will be around 1 km long (along with the rail line) in total, so a large area would be affected.

In other words,  the neighborhoods who currently walk to the station would now start to hear the trains in a way they have not heard them before.

Engineering_LXRA_Rail_Noise_Doc_ThumbThe LXRA document “Understanding rail noise and vibration” (available here) claims the proposed elevated structure would reduce noise and vibrations through:

  • Walls and screens to mitigate noise transfer
  • New high-quality, continuous smooth tracks
  • Purpose-built resilient fastenings to attach the new tracks directly to the structure
  • Rubber insulators under the track to dampen vibrations.

We did not find any claim that all noise impacts would be mitigated.

  • Walls and screens do help reduce noise but would add cost and visual impact. As a guide, the Caulfield-Dandenong (CD9) report indicates 600-2000mm high sound screens, the expectation being that these are attached to the side of the elevated rail – so screens up to 11m above the ground. (Great for those sea-view balconies!).
  • Continuous tracks could reduce the “clack clack” noises, but could also be used in a below ground option.
  • The use of fastenings and rubber insulators are not new to the rail space and could equally be applied to the below ground option.

As engineers, our concern is how well these mitigations will be working in 5, 10, or 50 years of constant use.

2B. Below Grade Rail Noise (In Ground Rail Design)

It is perhaps stating the obvious to point out that an in-ground rail line (the top of the train below surrounding ground level) would significantly and noticeably reduce rail noise compared to current “at-grade” noise levels.

Say NO To Sky Rail (Skyrail) - Frankston Line - Engineering - Noise Effects

Other than for those very close by, the noise would be largely contained as it was generated within two side walls.

3. But I heard on the news that an LXRA report for the Dandenong Line says there will be no extra noise if going up?

Engineering_LXRA_Rail_Noise_Doc_ThumbThis is referring to the “Preliminary Noise Report – Overview of Noise Impacts, Caulfield to Dandenong (Report: P03-000-CTD-XEV-0101)“.  The LXRA has published the Executive Summary (available here) and at first glance, it seems to be great news – zero change in noise against the design feature “Elevated structure”.  (See table below from the LXRA web page)

It’s a big claim that seems to say a lot and sounds great when reported in the media, but does it really mean anything significant at all?

We get lots of questions about this. Most people who have read this believe it means that there will be no extra noise from running trains on an elevated structure… What do you think it means?

Well unless you know how to interpret the full detailed report, it is misleading, but not actually a lie… The concrete structure itself, won’t make any extra noise!

“A summary of the potential noise impacts due to design features and the predicted change in noise is presented below:

Design feature Predicted change in noise
New continuously welded rail track 5dB reduction
Direct fix using resilient pads 6dB reduction
New stations 0-5dB reduction
Removal of level crossings 6-8dB reduction
Reduction in horn soundings 3-6dB reduction
Noise wall 5-15dB reduction
Vibration isolation 0-10dB reduction
Change in gradient 4dB reduction to 1dB increase
Elevated structure 0dB increase

The above factors are assumed to act individually. When considered in combination the net increase or decrease will not be equal to the sum of each individual component.

Compared to existing conditions where relevant noise criteria are not applied, the proposed design will achieve full compliance with relevant noise criteria. The proposed design will result in an overall reduction in noise throughout the corridor and surrounding area through the use of considered design measures. “
(LXRA Report: P03-000-CTD-XEV-0101, Page 18, “Table 15 – Summary of Noise Impacts”)

4. Our Response

Since you already know about the limits of the Government Noise Policy (Section 1 above), you’ll realize that “full compliance with relevant noise criteria” is not as comforting as it seems.

As was pointed out at the beginning of this article, ANY grade separation will reduce noise from the level crossing bells and horns.

Of course, the most asked questions we have had, have been about the “Elevated Structure, 0dB increase”. Most people have interpreted this to mean that there is no net increase in noise from putting the train tracks 9 metres in the air.

Look at the detailed report, not just the Executive Summary (you can find it here) and it makes more sense: This is from Page 17:

“Elevated Structures: The existing rail corridor is at-grade with no elevated sections. The proposed design will introduce elevated concrete structures which have the potential to generate structure-borne noise (noise due to the entire structure vibrating). Structure-borne noise is typically more pronounced in steel elevated structures than with concrete structures.”

So the noise assessed is just the noise from the vibration of the structure, not the change in elevation of the rails. Or to put it another way, how loudly the elevated structure hums. (Or maybe it doesn’t know the lyrics…) So not surprisingly, the estimated noise from this is not significant against the current background noise in that area.

We could not find any assessment of the noise impact of raising the rail 9 m in the air. Although, to be fair to the report author, this is something they may not have been asked to evaluate. We wonder, “Why not?”

On page 16 of the report, Noise Walls are discussed:

“The existing rail corridor contains no noise walls or noise reduction measures to reduce rail noise impacting on the surrounding community. The proposed design includes the provision for noise walls and visual screening at a number of locations. The proposed screens will vary in height between 600mm-2000mm. Noise barriers are most effective where they block line of sight between the receiver and the wheel/track interface. ”  

Common sense suggests that noise walls would only be used if the noise of a “Sky Rail” would be greater than the current at grade situation.

We look forward to more detailed noise reporting, in particular the “combination” evaluation of the overall noise impact of raising the rail, and a comparison of this with the current at-grade noise, especially for those not immediately adjacent to the rail line… and without noise walls.

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