Bad vibrations: Reducing noise and vibration levels on rail projects

Noise from rail lines can have a significant impact on local communities. Engines, brakes and moving wheels; warning bells and horns; and vibration from rail structures all cause noise which travels directly to nearby homes when the tracks are at street level. Minimising the impacts of noise and vibration was a key consideration in the design of the Caulfield to Dandenong Level Crossing Removal Project in Melbourne.

Demand for passenger rail services in Australian cities has grown significantly in recent years and is expected to continue. Growing populations are pushing the expansion of residential housing into areas previously used for commercial and industrial purposes, or that are, as of yet, undeveloped.

These changes will put more homes closer to rail lines and expose more people to noise and vibration impacts.

Design considerations for major rail projects

Construction is well underway on the Caulfield to Dandenong Level Crossing Removal Project, which involves the construction of three sections of elevated rail along the Cranbourne-Pakenham line, Melbourne’s busiest.

The project will remove nine level crossings and re-build five stations. It is one of several projects being run by the Level Crossing Removal Authority, which is overseeing the removal of 50 dangerous and congested crossings across Melbourne.

Project Director, Brett Summers, said that much of the Cranbourne-Pakenham Line does not perform well in terms of noise when compared to other examples of rail lines in Australia or overseas.

“This is largely due to the poor condition of the existing track; with rickety wooden sleepers and outdated metal equipment that, in some locations, vibrates and generates high levels of noise,” Mr Summers said.

Mr Summers said achieving this noise and vibration mitigation has been an integral part of the project’s design process, and a key consideration both in the design of the permanent works, and during the construction phase.

“Where many road or rail projects rely on standalone noise barriers to screen nearby properties from noise, this project has taken an innovative approach; building in treatments that mitigate noise at its source,” Mr Summers said.

“By providing a state-of-the-art rail system, we are effectively turning the volume of the rail corridor down. And not only will trains make less noise as they travel along the tracks, but there’ll be fewer horns and no more noisy boom gates.”

Mr Summers said there are a whole range of design features that will serve to reduce noise, right down to purpose-built fastenings and insulators under and around the tracks to limit vibration.

“Tailored screening will also be built into the façade of the structure, reducing not only noise but passenger visibility into neighbouring properties.

“Elevating the train tracks will make a significant difference to the amount of noise and vibration experienced by nearby residents – particularly those closest to the Caulfield to Dandenong rail corridor.

“Where street level tracks can project noise and vibration straight across to nearby homes, the elevated model combined with acoustic screening will re-direct much of that noise away from those properties.”

Assessing noise levels

The Victorian Government’s Passenger Rail Infrastructure Noise Policy, introduced in 2013,  provides transport bodies and planning authorities with a guide for the consideration of the impacts of rail noise from improved or new passenger rail infrastructure projects, and from changes to land use near existing and planned rail corridors.

The policy provides investigation thresholds (Table 1) to be considered when assessing the impacts of rail noise on nearby communities. The thresholds take into account residential dwellings and other buildings where people sleep, and noise sensitive community buildings. However, they are not a limit on allowable noise emissions.

Under the policy, the Caulfield to Dandenong Level Crossing Removal Project falls under the category ‘redevelopment of existing passenger rail infrastructure’.

“The Caulfield to Dandenong Level Crossing Removal Project has been guided by this policy in many ways, including the strategic placement of acoustic wrapping and screening in designs for the elevated structure,” Mr Summers said.

“We’ve applied the world’s best practice to noise modelling throughout the design process.

“Early on in the project we engaged the services of an acoustic expert, and they’ve so far been involved in assessing and monitoring both the existing noise and vibration levels, and modelling the noise and vibration levels associated with the elevated design.

“Acoustic models are produced using real world data. Measurements and surveys of the existing environment are fed into specialist acoustic modelling software, which applies mathematical algorithms to predict noise impacts.

“We measure those impacts in a three-dimensional area around the elevated structure that encompasses multi-storey apartments, as well as homes at ground level. So what we see on the model looks a little bit like a heat map, using colour to correspond with decibel levels.”

Mr Summers said the modelling also accounts for future operating conditions, such as the larger high capacity trains which will run on the line from 2019.

Taking the community into account

Managing rail noise has become a real challenge facing Australian cities as urbanisation increases across the country. Mr Summers said balancing the need for progress and public transport improvements with individual expectations will continue to be an area where engineers, designers and the community need to work collaboratively.

“The community has understandably expressed some concerns to us about the short-term noise they are experiencing during construction. However, we’ve found on the whole that people are very optimistic about the end result,” Mr Summers said.

The Final Noise Report: Overview of Noise Impacts Caulfield to Dandenong will be released in the coming months.

Table 1: Investigation thresholds for rail noise on nearby communities.