sydney-city-centre-review-of-environmental-factors

Affected roads
There are no screening criteria available in NSW or Australia to determine if changes
to an existing road would be sufficient to ‘affect’ (impact) adjacent receivers. As such,
the assessment adopted the following screening criteria from the UK Design Manual
for Roads and Bridges:
An alignment change of greater than five metres
A change (increase or decrease) in traffic flow of more than 1,000 vehicles
each day
A change (increase or decrease) of more 200 heavy vehicle numbers each day
A change (increase or decrease) in daily average speed of more than 10 km/h
A change (increase or decrease) in peak hour speed of more than 20 km/h.
The only screening criterion satisfied under the proposal would be localised traffic
flow changes at various points across the proposal footprint created through the
introduction of the traffic capacity improvements. This was determined by referring to
the intersection traffic modelling data discussed in section 6.1. Importantly, the
modelling data only considered the change at the immediate intersection. It did not
consider the effects elsewhere on the road network. However, as discussed in
section 6.1.2, traffic volumes in the city centre are anticipated to plateau into the
future. Consequently, whilst the capacity introduced along the roads considered in
this proposal would result in a localised increase in traffic, it is expected that there
would be other parts of the road network where traffic volumes would decrease,
notably for example along part of George Street once it is closed to traffic. Arbitrarily,
the air quality of the immediate road corridor in these locations would slightly improve
whilst slightly decreasing along the roads subject to capacity improvements under
this proposal. This is discussed further below.
6.12.2 Existing environment
Meteorological conditions
Sydney’s temperate subtropical climate is generally characterised by very warm
summers and mild, warm winters. Average daily temperatures generally range
between 18 degrees Celsius ( o C) and 26 o C during summer and between 9 o C and
18 o C during winter. Uniform rainfall is experienced throughout the year with an
average of 1,287 millimetres received per annum at Observatory Hill (Bureau of
Meteorology, 2014). Autumn is typically the wettest period, while spring is generally
the driest.
The meteorological conditions would affect dust dispersion during the works.
Generally, the urban environment provides greater shelter; however, the wind can be
channelled along streets, with other wind effects occurring around buildings. This
only becomes a problem with high-rise development, where the corridor effects can
be significant. The ambient average wind speed (as measured at Observatory Hill,
itself an exposed location) varies. In the morning in the summer months it is lower
(8 to10 metres per second (ms -1 )) compared to the winter months (10 to 13 ms -1 ).
However, in the afternoon (due to differences in the land/sea temperature) the wind
increases. It is generally lower in the autumn (13 to 15 ms -1 ) compared to the rest of
the year (15 to 20 ms -1 ).
Due to the variability in local meteorological conditions and soil characteristics there
is no absolute limit above which wind-blown dust becomes a problem. Generally
however, some guidance documents quote that above 7.5 ms -1 dust may become an
issue and above 8 ms -1 dust suppression controls should be put in place, as dust
would mobilise, and above 15 ms -1 , works should stop temporarily, as described by
Sydney City Centre Capacity Improvement 396
Review of Environmental Factors