Here’s our Drive-by Assessment specification that we've been working on the Tasmanian Government's Department (DSG) of State Growth.
DSG are working on their Traffic Management Plan and I'll encourage them to share that as well. This is really important because the risk of assessing trees on a high-use road is much higher than the risk of branches or trees falling on a high-use road.
It can be adapted to meet your needs. By way of explanation for how this is set up. It’s part of the Government Tree Risk-Benefit Management Strategy. So, you’ll need to be familiar with that to understand the difference between Passive Assessment & Active Assessment. And the three levels of Active Assessment – Basic, Detailed, and Advanced.
Zones of high confluence = High use + large trees
In VALID that’s 1400 or more vehicles a day. The speed limit doesn’t matter. For people, we’re looking at around 1200 per day. This translates to someone passing every minute or so between 7am – 7pm, Mon – Fri. Large trees, for purposes of zoning rather than assessment are trees with a DBH of about 50cm/20in or more.
Drive-bys can be carried out by a Basic Validator or a Validator. This is released under a creative commons licence, and you're welcome to replace these trained assessor titles with whoever would be carrying out a Drive-by Assessment and what their credentials are.
Putting tree risk into perspective.
A neat and easy to understand relative risk came up in Tim Harford’s marvellous Cautionary Tales - The Spreadsheet of Life and Death. Driving for 200 miles (320km) has a risk of death of about one in a million (1 micromort).
We know the overall risk of death from branches or trees falling each year is less than one in a million (less than 1 micromort).
That means you’re exposing yourself to a higher risk of dying by travelling in a car on a 200 miles round trip to visit friends for the weekend, than you are being hit by a branch or tree over the whole of a year.
Duty holders who don't have a strategy explaining how they manage the risk from tree failure are vulnerable to legal claims or enforcement action. Even though we know the overall risk of death or serious injury from tree failure is extremely low, a number of recent Coroner's Inquests from around the world have highlighted why having a strategy in place is so important.
Death on the highway, from the Arboricultural Association's Arb Magazine (Summer 2020), takes a closer look at the importance of Tree Risk-Benefit Management Strategies to the duty holder.
Here's a LinkedIn article about the landmark Cavanagh v Witley Parish Council Judgment. It explores the gulf between reasonable, proportionate, and reasonably practicable tree risk assessment and management, and expert evidence in some UK court Judgments.
Poll v Bartholomew 2006
Every summer, when we get long hot dry periods, concern is often raised about the risk from Summer Branch Drop (SBD). Fear not. We’ve got the risk management of SBD covered for you in our free Summer Branch Drop (SBD) Guide.
Is this SBD?
In brief, the overall risk from SBD is mind-boggling low. What that means is there’s no need to fret about putting up signs, or fencing, or pruning, unless you have a tree that’s a repeat offender.
Have a look at our Risk Management page for lots more free and handy common sense tree risk management advice and help.
When a tree might be 'dangerous'*, it'll usually have obvious features (not tree defects) that you can't help but notice.
To help you spot trees that might be dangerous, here's an illustrated Obvious Tree Risk Features Guide for you to download.
We're a not-for-profit and this is released under a creative commons licence, so we're more than happy for you to share it around.
*Dangerous = where the risk is not Acceptable or Tolerable.
A short piece about why we shouldn't use 'risk of harm' when talking about tree risk.
The risk of harm?
'Tree Defect' no longer appears in any of VALID's Tree Risk-Benefit Management Strategies.
Want to know why we're 'ditching the defect' here, and the App is going to have a ? added to D for DEFECT? Click the link to this short article to find out.
Taking the 'Defect' out of tree risk-benefit management strategies
Most of the research into ‘Tree Architecture’ (Arboritecture) is from France and Canada. That means it’s published in French, which many of us can’t read. This piece by Tom Joye, in the UK’s Arboricultural Association’s Arb Magazine, is a great introduction to the world of Tree Architecture, and what it can reveal about the ‘development stage’ of a tree. It’ll have you look at growth and epicormic growth in a different way.
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