2019-03-12 P&E Agenda - Item 5 - Attachment 2 - Koala Infrastructure & Feasibility Report

•    Financial considerations may dictate non-structural approaches to collision reduction but structural
     methods are probably more effective (and more expensive).
•    The efficiency of road mortality mitigation approaches should be determined via a post-implementation
     monitoring program.

3.3.1.          Road design
Increases to human population and urbanisation leads to increased road density and traffic volumes, it is
critical to plan for these changes while limiting their impacts to biodiversity (McKinney 2002; Sushinsky et al.
2013).

Clevenger et al. (2003) examined the spatial patterns and factors influencing small terrestrial vertebrate
road-kill aggregations along roads varying in traffic volume, configuration and adjacent landscape attributes
in the Bow River Valley, Alberta, Canada between 1997 and 2000. The study found that road-kills tended to
occur close to vegetative cover, far from wildlife passages or culverts and were less likely to occur on raised
sections of road. Where possible, road reserves should be maintained to minimise habitat or resources that
may attraction of wildlife to roadsides (Rhodes et al. 2014). We note that while this is applicable to grazing
wildlife, road reserves often provide important corridors for koala movement due to vegetation clearing
elsewhere.

The literature suggests that vehicle speed and traffic volume are probably the most important factors
explaining wildlife collisions (Clevenger et al. 2003). Where vehicle speed and/or road density are high, road
traffic has been shown to have a severe local effect (Jones 2000). Dique et al. (2003) observed that the risk
of collision between a vehicle and a koala is greatest when high volumes of traffic moving at high speeds
travel through areas of relatively high koala population density. Preece (2007) found that road segments with
roundabouts in Brisbane had significantly less koala mortality than expected compared with secondary roads.
Roundabouts or other traffic-slowing devices could be considered for key locations where koala movements
occur over roads (Goldingay & Dobner 2014) and it is impractical to implement other hard infrastructure
measures. Effective mitigation at such locations requires insight into the effects of road and traffic
characteristics on both wildlife movements and traffic mortality (van Langevelde et al. 2009).

The two key ways in which growth in vehicle numbers can be accommodated result in different spatial
distributions of traffic and therefore contribute to wildlife mortality rates via two different processes (Rhodes
et al. 2014). Firstly, existing roads can be upgraded to carry higher volumes of traffic, effectively increasing
traffic volume while road density remains constant. This leads to higher mortality rates as the probability
that an animal crossing a road is hit by a vehicle increases. Secondly, the number of roads can be increased,
effectively increasing the road density while traffic volume remains constant. This leads to higher mortality
rates as the probability that an animal moving around the landscape will cross a road increases. Using a
spatially-explicit simulation model to quantify the relative impact of changes in road density and/or traffic
volume on mortality rates for a koala, Rhodes et al. (2014) showed that the effect of road density on mortality
is commonly higher than the effect of traffic volume. The opposite was only true when road density was very
low and traffic volume very high. Therefore, under most circumstances, it is preferable to accommodate a
greater number of vehicles by increasing the capacity of existing roads, rather than building new roads. It is
only in cases where the existing road network is characterised by very few high capacity roads that increases
in network capacity by building new roads is likely to have the least impact on koala mortality.

If new roads are necessary, alignments should avoid locations close to existing habitat and complementary
strategies such as traffic calming in key habitat areas and redirecting traffic to surrounding roads during
crucial periods should be considered (Rhodes et al. 2014). Jaarsma et al. (2006) developed a model for the
probability of successful road crossing by mammals to compare alternative network solutions and evaluate
traffic calming measures on wildlife-vehicle collisions. The results presented in Table 1 show that the highest

Koala Infrastructure Audit & Feasibility Report                                                           Page 16

Noosa Council
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