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How we helped assessing safety risks in regional Victoria

Background

Victoria’s Towards Zero 2016-2020 Road Safety Strategy and Plan sought a 20% reduction in deaths and 15% reduction in serious injuries over a five-year period. This plan recognised the need to create a safe system which included changes to the road infrastructure to achieve this target. The Side Roads Activated Speeds (SRAS) treatment trial is an integral part of the Safe System Road Infrastructure Program (SSRIP), that the Department of Transport (formerly known VicRoads) and the Transport Accident Commission (TAC) are collaboratively working towards to save lives and support the Towards Zero 2016/2020 plan.

 

It has long since been understood that the risk of serious injury or death for impact crashes is significantly decreased for lower speeds. It therefore stands that to create a safe system at a rural intersection, travel speeds through intersections where there is a potential for collision should be reduced – the installation of SRAS treatments was one way this could be achieved.

 

Objectives

The objective of this project was to evaluate the safety benefits of the SRAS treatment in Victoria, by assessing the speed reduction (crash severity), gap acceptance changes and Post Encroachment Time (crash likelihood) at a total of 9 intersections. Such evaluation projects provided an opportunity to apply learnings to improve future investment decisions. VicRoads’ Investment Evaluation Framework provided guidance on various quantitative, qualitative and mixed criteria to evaluate its investments. It is well established within this framework, that a reduction in traffic speeds improves road safety – it therefore stands that through the measurement of speed profiles as well as surrogate safety metrics such as GAP, GAT and PET at trial locations, we could assess the effectiveness of SRAS treatments in terms of road safety.

 

Scope

As with all evaluation projects, collecting data which is reliable and robust is critical to the success of this evaluation project. DoT and SMEC understood the need to collect the right type of data and therefore engaged Real Time Traffic (RTT) after a careful and thorough selection process to deliver data through innovative radar, WIFI and computer vision technologies.

 

The data collection period was three weeks and the reason being to ensure sufficient data was collected to achieve desired statistical significance as these rural sites had very low traffic volumes.

 

Our Technology

WIFI Technology for Segment Speed

RTT deployed Wi-Fi devices to collect segment speed data at approaches to the intersection (refer to WIFI technology for more information).

 

Radar Technology for Spot Speed

Radar technology was used to collect spot speed, volume and classification data at the intersection. This was a cost effective non-intrusive, off-road technology with a remote access capability to enable live survey monitoring.

Each radar was mounted at 6 – 8m high on self-standing structure with a small footprint. The structure houses a solar-power system with high-capacity back-up batteries. This configuration guaranteed optimal operability with no down time over an extended period of time i.e. months.

Figure 1: Radar Technology Concept

 

Computer Vision Technology for Conflict Analysis

RTT deployed state-of-the-art computer vision CCTV technologies highly sought after on all of our projects. Video surveys was undertaken using high definition, PTZ (Pan, Tilt, Zoom) CCTV cameras deployed throughout all project treatment and control sites. Similar to radars, cameras were solar powered mounted on a self-standing structure with solar power system and back up batteries. This configuration guaranteed optimal operability with no down time during the entire duration of the surveys.

Figure 2: Hardware platform

 

Proactive Safety Metrics for Conflict Analysis

The conflict analysis included the key surrogate safety measures Gap Acceptance Time (GAT), Post Encroachment Time (PET), GAT Time, Gap Acceptance Time, Lane positions and stop line compliance (check out How Our Technology Works)

It was proposed to adopt the below approach as initially introduced by Allen et al. (1977), to measure PET. It is defined as the time between the moment that the first road-user/vehicle leaves the path of the second and the moment that the second reaches the path of the first (see Figure 3) The PET value indicates the extent to which they missed each other.

Figure 3: Visual Representation of Post Encroachment Time (PET)

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