2016-02-02 I&S Committee - Item 4 - Attachment 1 - Noosa Traffic Study

3 YEAR 2015 TRAFFIC ANALYSIS – EXISTING CONDITIONS
3.1 Discussion of traffic analysis principles
The majority of traffic capacity issues in an urban road network occur at intersections.
Therefore, this study has primarily focused on the performance of intersections at critical
locations throughout the network. The majority of traffic capacity issues will arise in the
populated coastal areas, but there are also existing issues outside of the main population
areas, such as at Cooroy, which are also assessed.

Capacity analysis of the intersections has been undertaken using the industry standard SIDRA
computer based intersection modelling package. The SIDRA package is widely used
throughout Australia and is recommended by the DTMR. It has been refined over several
decades, and is calibrated based on large amounts of research and case studies.

It is noted that there was initial concern expressed that the standard SIDRA roundabout
operational parameters may not be representative of Noosa Conditions due to Noosa being a
tourist town, and also due to Noosa having a higher than average proportion of the retirees.
The inference being that SIDRA may overestimate the capacity of roundabouts in Noosa,
because the higher proportion of tourists and retiree road users may wait for larger gaps in
traffic before entering the roundabouts. However, critical operating times at the majority of
major intersections within the Coastal Area road network occur during the AM and PM weekday
commuter peaks, when tourist traffic and retiree traffic is typically a low proportion of the
network demand. Furthermore, review of the intersection video recordings, used to identify
peak period traffic flows, at the more critical intersections of the Noosa Road network, indicates
that SIDRA appropriately models those critical intersections. The reviewed intersections
included the following:

      Poinciana Avenue / Moorindil Street
      Memorial Avenue / Doonella Street
      Ernest Street / Hilton Terrace
      Beckmans Road / Eumundi Noosa Road
      David Low Way / Heron Street

The intersection layout (traffic lanes, traffic lane lengths, slip lanes, etc.), form of intersection
control (“give way”, roundabout, traffic signals), traffic volumes, and other parameters are input
to the SIDRA package. The model then outputs a series of parameters to indicate how the
intersection is operating under the input traffic loadings.

Intersection performance in a capacity sense is measured primarily by the “Degree of
Saturation” (DOS), which is one of the performance parameters output by the SIDRA package.
This is the most commonly quoted intersection capacity analysis parameter and identifies the
proportion of intersection capacity utilised. For example, a DOS of 0.80 means that 80% of
intersection capacity is being utilised. A DOS of 1.0 indicates that the intersection is operating
at capacity, with constant queuing on critical approaches to the intersection.

For traffic planning at roundabouts, which are the form of intersection at most major junctions
within Noosa, the widely quoted desirable limit for the degree of saturation is 0.85. When a
roundabout reaches a degree of saturation of 0.85 during the peak hour, there will be periods of
queuing and delays at the roundabout, and there will also be periods of more free flowing
conditions. A degree of saturation reaches 1.0 indicates that there will be a constant queue on

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