COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL
MEETING OF LUCAN/PALMERSTOWN/FONTHILL AREA COMMITTEE
Tuesday, January 28, 2020
QUESTION NO. 6
QUESTION: Councillor L. O'Toole
To ask the Chief Executive for a report on noise barriers / boundary along the N4, what type of barriers were placed along both sides of the N4 in its first design/upgrade, when they were installed and to include what traffic volume the noise barriers were designed for (appx 20 years+) and compare it to todays volume of traffic using the N4. If the Chief Executive could comment on whether it supports introducing updated more effective noise barriers should studies/findings confirm if new ones are required.
REPLY:
The EIS for the Lucan Bypass Upgrade Scheme was published in February 2005.
Traffic projections were provided in Chapter 5 for the base year 2008 and the Design Year of 2023.
The current traffic flow recorded by a TII Counter on the Lucan Bypass is as follows;
| 2019 | 2018 | 2017 | |
| AADT | 86498 | 83989 | 83065 |
| % HGV | 4.6% | 4.0% | 3.8% |
| Coverage | 84.3% | 99.7% | 99.7% |
The EIS records the projected design year traffic flow for the same location as 122,500 AADT.
Thus the existing traffic flow (2019) is only at 70% of the projected flow, (ie 86,498 AADT vs 122,500 AADT).
Based on the foregoing, the noise mitigation measures in place are adequate to cater for the current traffic volumes and there is no requirement to revisit the existing situation until at least 2023.
Clause 7.4.2 of the EIS sets out the Design Goals For Specifying Noise Mitigation Measures
Cl 7.4.2 Design Goals For Specifying Noise Mitigation Measures
For new roads in Ireland, it is standard practice to adopt traffic noise design goals contained within the NRA document Guidelines for the Treatment of Noise and Vibration in National Road Schemes (2004). This document specifies that the Authority (i.e. NRA) considers it appropriate to set design goals for Ireland as follows:
- day-evening-night 60dB Lden (free field)
These design goals represent more onerous limit values than those that have typically been employed in Ireland to date.
Noise mitigation measures are deemed necessary whenever all of the following three conditions are satisfied:
- the combined expected maximum traffic noise level, i.e. the relevant noise level, from the proposed road scheme together with other traffic in the vicinity is greater than the design goal, and;
- the relevant noise level is at least 1dB more than the expected traffic noise level without the proposed road scheme in place, and;
- the contribution to the increase in the relevant noise level from the proposed road scheme is at least 1dB.
Noise barriers as described in Chapter 7.4 of the EIS were used to achieve a Design Goal as outlined above for the projected Design Year traffic flow at each section of the route.
The barriers comprise timber panels that were installed in front of and projecting above the existing concrete block boundary walls. On-site tests were undertaken during construction to ensure that the required level of noise reduction was achieved by this hybrid arrangement.
In conclusion, any future assessment of noise along on the N4 will be a matter for TII as this road is now in their charge.