Arboricultural case study

Highways Agency Managing Agent

Key features Client: Highways Agency Managing Agent

Site location: trunk road, Surrey

Site description: busy section of trunk road, passing through area of outstanding natural beauty

Site challenges: history of tree wind throw and tree failure, resulting in serious injury and fatality.

What PBA did

PBA Consulting prepared a report identifying and recommending hazardous tree management strategies. It included a 10-year plan of operations for this busy section of trunk road in Surrey. Given the hazard levels and potential risk to human life, there was a overriding need to demonstrate agent's duty of care.

The report reviewed current best practices and provided guidelines for the management of highway trees. It included a proactive tree management strategy emphasising highway safety.

A busy route with a hazardous history

The single carriageway trunk road runs through an Area of Outstanding Natural Beauty. It connects the south coast to London and beyond. It is a busy route that often has standing traffic for long periods. There has been a history of tree wind throw and tree failure, resulting in serious injury and fatality.

There were a large number of major trees close to the road or within the ditch line adjacent to the highway. Should these trees fail, potential targets included vehicles, pedestrians and services such as electricity, telecoms, property and street furniture.

Scope of PBA work

The scope of the PBA Consulting report included:

• Documents and key legislation covering highway management and current best practice. References included Highway Act 1980, Health and Safety at Work Act 1974, DETR Circulars and Research Series such as Principles of Hazard Assessment and Management and Arboricultural Association Guidance Notes.
• Detailed Visual Tree Assessment (VTA) covering tree health, defects, site conditions, conservation issues and biodiversity plans.
• Assessment of the impact of tree management practices such as phased tree removal, selective thinning, crown reduction and thinning.
• Identification of all trees requiring management work by tag, photographs, and positional data.

Report recommendations

Trees are dynamic. Proactive management would identify potential hazards and reduce risks. To reduce medium/high risk categories, the following recommendations were made:

• Assess the safe, useful life expectancy of trees within their context to foresee any potential hazards.
• Identify and manage trees with certain characteristics that may become hazards.
• Take into account the effect of weather and wind loading pattern on trees.
• Mitigate risks by removal of mature trees which are in decline and have limited life expectancies.
• Manage and develop suppressed trees along the ditch lines to provide valuable 'safe' highway trees for the long term
• Put in place strategies within the management plan to maintain bio-diversity.

Key client benefits

• Regular tree inspections to minimise failure
• Treescape preserved - minimal effect on Area of Outstanding Natural Beauty
• Reduced risk to road users, property and utilties
• Clear demonstration of agent's duty of care

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