Do hedges and trees block road noise?

Do hedges and trees block road noise?

A normal garden hedge barely does. A measured study of thick dense hedges (Van Renterghem and colleagues, Applied Acoustics, 2014) found reductions of up to about 3.6 dBA for light vehicles at roughly 20 to 55 km/h, with typical medians of about 1 to 3 dBA. A deep, dense belt of planting about 30 m wide gives roughly 5 dB or more, according to US highway guidance, and that is far more depth than most gardens have.

Many people overestimate the effect. A hedge hides the traffic, which can change how the road feels but not the sound level (see the perception section below). A change of 3 dB is about the smallest that people can typically notice, according to a Forest Research guide (2025), and the measured hedge reductions are mostly just under that size. Our guide to what decibels mean explains the scale.

What did the hedge measurements find?

The Van Renterghem study measured thick, dense hedges against light vehicles at low speeds. A 2 m thick, 4 m high spruce hedge gave about 1.1 to 2.2 dBA, and a 1.9 m thick, 1.6 m high hawthorn hedge gave a median of about 1.9 to 2.8 dBA. The authors link the larger reductions mainly to ground effect, which they find dominates over the plant material above ground, with foliage and twigs mattering mostly above 1 kHz. Results vary from hedge to hedge and the paper does not give an A-weighted total for every one, so treat the individual hedge figures as approximate.

Other sources point the same way. Caltrans' Technical Noise Supplement (2013) puts ordinary landscaping at under 1 dBA, and Hothersall's paper for the Institute of Acoustics says hedges and thin belts provide very little screening.

How deep does planting have to be?

Depth and density matter most. Attenborough and Taherzadeh, writing for the Institute of Acoustics, summarise a study of 35 tree belts: sparse belts gave under 3 dBA, medium belts 3 to 6 dBA and dense belts over 6 dBA, with depth the most important factor. Hothersall reports deciduous belts 15 to 40 m wide giving about 4 dB or less (approximate; the source scan is poor), and a dense evergreen belt 10 m wide giving 4 to 5 dB. The US Federal Highway Administration (FHWA) says dense planting at least 5 m high and 30 m wide may give up to 5 dB(A).

Forest Research's 2025 guide, written with the Trees and Design Action Group, says buffers 10 to 15 m wide can cut road noise by up to 6 dBA compared with grass alone. It also quotes a US example of a buffer 30 m wide and 9 m tall, at least 6 m from the road centre and with low traffic speeds, giving 5 to 8 dBA.

The same guide says relatively narrow buffers or single lines of trees can give up to 5 dBA compared with shrubs (a single line of dense conifers with shrubs). That is more optimistic than the hedge measurements, and the evidence is not fully consistent. Separately, a Forest Research web page says five to ten decibels for every 30 m of woodland. The page and the guide conflict. We use the guide's lower range, as the more recent and detailed document, and treat the higher figure as optimistic.

None of these is a garden hedge. A belt 10 to 30 m deep is closer to a small wood than to a boundary planting.

What changes with the seasons and the ground?

Deciduous planting loses up to about 3 dBA in winter compared with full leaf, according to the Forest Research guide, which recommends mixing evergreen and deciduous species. Evergreens keep working through the year.

Much of what planting does comes from the ground it grows in. Attenborough and Taherzadeh list ground effect from leaf litter, scattering by trunks and branches, and foliage as the main mechanisms. FHWA gives 3 dB(A) per doubling of distance for a line source, plus an extra 1.5 dB(A) per doubling over acoustically soft ground, for low incident angles and distances up to about 30 to 60 m. The 4.5 dB total is our sum, not a figure FHWA states.

Do trees help behind a solid fence?

We found no evidence that planting behind a solid fence adds a measurable amount, and we have not assumed that it does. Hothersall's worked example hints at one reason: the ground's effect over grass is lost once a barrier is in the way, so some of what soft, planted ground contributes disappears. In that example the net gain from the barrier was only 1.8 dB(A).

Does hiding the road make it sound quieter?

The evidence here is limited. The Forest Research guide, written with the Trees and Design Action Group, says views of greenery can reduce perceived road traffic noise by up to 10 dBA. A 2010 survey (Li, Chau and Tang, Science of the Total Environment; 992 interviews, 688 usable responses) found that how people perceived greenery had a considerable influence on the noise annoyance they rated at home.

Neither changes the sound level. Planting may still make a garden feel better, and the Forest Research guide suggests birdsong may draw attention away from traffic. It is not a substitute for a barrier.

What works better than a hedge?

A solid, gap-free barrier that breaks the line of sight to the road is better evidenced. FHWA says about 5 dB when the line of sight is only just blocked, approaching 10 dB for a well-designed barrier. Our guide to the best fence or wall for road noise sets out what the evidence says.

Where you sit also matters. Putting seating behind the house or an outbuilding can do more than planting, as our guide to reducing road noise in your garden explains. Planting is still worth having for how the garden looks and feels, just not as the main noise control.

Limits of this evidence

The hedge study covered light vehicles at roughly 20 to 55 km/h, so it does not tell us about faster roads or heavy vehicles, and its individual hedge results vary. The belt figures come from highway and woodland studies in different countries and plantings, and none is a typical garden. Forest Research's own sources conflict, as above. The perception evidence is one survey and a guide statement, and neither changes the sound level.

Every figure here is a published value for a type of planting. None is a measurement or a guarantee for your garden.

What is a sensible next step?

If you want to know how noisy your garden is, a modelled estimate for your address is the place to start. The noise check gives a plain-language rating for road and rail noise at an address, and the Fence Feasibility Check models whether a barrier is worth considering. Both are modelled estimates, not measurements.