Capability: Traffic Safety Modelling

Example application 1: Comparison of existing network performance against local average crash rates (intersection crashes only are shown, for simplicity)

Example application 2: Changes in future predicted crash costs with a proposed major roading scheme, compared to Do-Minimum. (Intersection crashes only are shown, for simplicity)

Launched in 2010, Safer Journeys is a strategy designed to guide New Zealand's efforts to improve road safety from 2010–2020. Its vision is for:

“A safe road system increasingly free of death and serious injury”

QTP have developed an interface for Christchurch City Council which can assist achievement of this vision, as it enables the potential road safety implications of future road network supply and transport demand scenarios to be estimated.

The interface uses a detailed traffic model for the prediction of road network demands across the wider conurbation. The comprehensive and accurate nature of the base year traffic model coverage allowed local crash-rate models to be estimated which take account not only of where crashes did occur – but also where they did not. This is potentially a significant improvement on many existing approaches to crash prediction.

Essentially, local crash-rate models were developed using records from the NZTA’s CAS (Crash Analysis System) combined with traffic flow estimates derived from the base year traffic model. These crash models, when coupled with the ability of the traffic model to predict network-wide traffic volumes, enables estimates of the future (safety) performance across the network to be made.

For both individual intersections and link (‘mid-block’) road network elements:

• Where the network remains unchanged, calibrated intersection and link-specific models can be applied; and

• Where network change is proposed, appropriate ‘generic’ average ‘rate’ models are determined for the particular application, and applied.
• Optional adjustment can be made for potential future trends in general road crash rates, compared to base period rates.

Given future network configuration, land-use distribution and resulting travel demand patterns, the future network safety performance can now be investigated. The interface allows the number of expected crashes (both reported and corrected for under-reporting) and anticipated annual crash costs to be readily estimated.

The network-wide nature of the traffic model allows the potential for crash-migration to be taken into account when assessing potential network and land-use changes.

Such information can be of high value for:

• the assessment and prioritisation of alternative transport investment and land use development strategies;
  
• determining potential positive and negative road safety effects of individual schemes or packages; and
  
• infrastructure funding applications.
  

For more information, please see this Summary Presentation or read a Background Report, 
and contact Paul Roberts for a discussion on how we may assist you.