The holidays are nearly here, along with the seasonal ad campaigns reminding us to play it safe on the roads (thanks Waka Kotahi). Unfortunately the need for these are not going away, and I’m sure we have all witnessed alarming behaviour, such as poor overtaking attempts when stuck in slow traffic queues. This seems especially true during the summer months when lots of people are travelling across long distances and campervans and other slow vehicles are rife. Read on about this second blog in our series on SafeView, you can catch up on the first one here.
SafeView is a tool that can be used to assess sight distance across the whole road network. This can help us to find locations that might have a high risk of unsafe overtaking, or where poor visibility could lead to head-on crashes. As part of a series on the SafeView project, this blog looks at the results of a literature review, and includes what I’ve found out about the importance of providing regular overtaking opportunities. It also briefly touches on my initial work with the Crash Analysis System (CAS) data.
Overtaking demand, sight distance and crash rates
Overtaking demand occurs when one driver catches up to another but would like to maintain their speed. If drivers don’t have the opportunity to overtake, they can get frustrated, which may lead them to make poor and unsafe decisions.
The Safe System philosophy, which underpins the Road to Zero approach, is focused on building a system that helps to keep users safe, even when they make mistakes. For this reason, it is important to provide suitable opportunities for overtaking.
Over the past few weeks, I’ve been reading official reports and research papers in order to investigate our current understanding of overtaking demand and when opportunities should be supplied. These point out what we know intuitively – demand increases with high traffic volumes and poor forward visibility.
Passing facilities (such as passing lanes) can help relieve this pressure. However, their design and location will impact how well they perform. They may also be too expensive to build. The best alternative is to make sure there are places where drivers can see far ahead enough to perform overtaking safely.
Exploring crashes on New Zealand roads
Every time that police attend a crash, a report is generated and added to the CAS database. This provides a rich source of information about what is happening on New Zealand roads.
In considering overtaking related crashes, the first step was to exclude crashes happening outside our area of interest, which is on rural high-speed two-lane roads. Of all the recorded crashes, 5.7% were related to overtaking and 16.7% were on rural high-speed roads.
The initial review will help to inform our analysis, especially as we begin to peel back the layers and identify important contributing factors to these crashes. In my next blog, I will discuss what I have uncovered so far and the limitations I am facing as I continue working with the crash data.