10Construction, backup beepers and leaf blowers

The short version: The standard US table of construction noise comes from the Federal Highway Administration, and its numbers trace back to the specifications Boston wrote for the Big Dig. Measured at 50 feet, an impact pile driver hits about 101 dBA Lmax, a concrete saw 90 and a jackhammer 89. The backup beep exists because US federal workplace rules require a reverse alarm audible above site noise - but OSHA has said that alarm does not have to be a beep, which is why some trucks now hiss instead. Gas leaf blowers measure roughly 65-80 dBA at 50 feet and carry far because of their low-frequency sound; electric models measured about 10 dB quieter in one study, and whether to ban gas blowers is an active local fight.

How loud is a jackhammer?

What you hear: A rapid, metallic hammering that rattles windows, usually starting right when the work day does.

In the FHWA's table, a jackhammer measured 89 dBA at 50 feet (15 meters), against a specification limit of 85.¹⁹¹ All the figures below come from that same table, Table 9.1 of the FHWA Construction Noise Handbook, which feeds the agency's Roadway Construction Noise Model (RCNM) - the software US highway projects use to predict construction noise.¹⁹¹

Every number is Lmax in dBA, slow meter response, at 50 feet. Lmax is the highest level reached during the measurement - the peak moment, not an average over the day.¹⁹¹

Source for every row: FHWA Construction Noise Handbook, Table 9.1.¹⁹¹

Two things stand out. The impact tools - pile drivers, hoe rams, jackhammers, saws - sit at the top, and several machines measured louder than the spec that was supposed to limit them. The pile drivers came in 6 dB over.¹⁹¹ Decibels are logarithmic, so 6 dB is about four times the sound energy.

Why does every US construction noise table look the same?

What you hear: Nothing - but if you have ever read an environmental impact statement for a road or rail project, you have seen these numbers.

The RCNM equipment list was not built from scratch. The FHWA handbook says its specification values come from the Central Artery/Tunnel (CA/T) project - Boston's "Big Dig" - specifically CA/T specification 721.560.¹⁹¹ The spec limits were set at levels the CA/T contractors could achieve, and the handbook notes that pile drivers often exceeded spec.¹⁹¹

So a noise study for a highway widening in Texas or a transit line in California today may be leaning, at least in part, on limits written for one Boston megaproject. That helps explain why so many of the limits come in round fives (80, 85, 90, 95): they began as contract limits, not reference values.

Why are construction numbers always "at 50 feet"?

What you hear: A jackhammer that sounds like it is in the room when you are across the street, and fades to a tapping a block away.

Distance changes everything, so a decibel figure with no distance is close to meaningless. The RCNM table fixes the distance at 50 feet so every machine can be compared on the same footing.¹⁹¹ For a single machine in the open, sound drops by roughly 6 dB each time the distance doubles. By that rule of thumb, an 89 dBA jackhammer at 50 feet would be around 83 dBA at 100 feet and around 77 dBA at 200 feet, before buildings, walls or other sounds get involved. Reflections off a street canyon can make the real drop smaller.

Two cautions when you hold these numbers up against a city noise rule:

• Lmax is not Leq. A city limit written as an average over time (Leq) and a peak reading (Lmax) measure different things. A jackhammer's 89 dBA Lmax does not mean the average level on the block is 89.
• The measuring point matters. Many city codes measure at the property line of the person complaining, not at 50 feet from the machine. Check what distance and metric your local rule uses before comparing.

Why do trucks beep when they back up?

What you hear: Beep... beep... beep, steady and piercing, at 6 a.m., from a dump truck you cannot see.

In the US, the beep comes from OSHA's construction rules. Under 29 CFR 1926.601(b)(4), no employer may use motor vehicle equipment with an obstructed rear view unless "the vehicle has a reverse signal alarm audible above the surrounding noise level" or "the vehicle is backed up only when an observer signals that it is safe to do so."¹⁹² A parallel rule for earthmoving and compacting equipment, 1926.602(a)(9)(ii), requires "a reverse signal alarm distinguishable from the surrounding noise level" or an employee signaling.¹⁹²

Read those carefully and you can see why backup alarms are so loud: the legal test is to be heard over a construction site, which is itself one of the loudest places in a city. An alarm tuned to cut through a running excavator will carry a long way down a quiet residential street. The rule also offers an alternative - a human spotter - which is why you sometimes see a worker waving a truck back with no beeping at all.

Alarms are sold in loudness classes. The SAE J994 standard rates them with a microphone 4 feet (about 1.2 m) from the horn on its axis: Type A at 112 dBA, Type B at 107 dBA, Type C at 97 dBA, Type D at 87 dBA and Type E at 77 dBA. ¹⁹³ Those are the standard's class levels, not field measurements on a street.

Why do some backup alarms sound like static instead of beeping?

What you hear: A harsh "shhh-shhh-shhh" pulse, like bursts of radio static, from a reversing truck.

That is a broadband or "white noise" backup alarm: instead of a single pitch, it hisses across a wide spread of frequencies. In a May 27, 2004 interpretation letter, OSHA wrote that the reverse-alarm provisions "by their terms, do not specify that a reverse signal alarm be of the single-tone type," and that a white-noise alarm complies if it warns workers in, or walking toward, the vehicle's path in time.¹⁰⁶

The appeal is direction. The brain locates a sound by comparing the timing and level differences between your two ears and by the way your outer ear filters sound, and those cues work best on broadband sound with lots of frequencies in it.⁹⁵ A pure beep gives the brain less to work with, especially when it bounces off buildings - which is why a tonal beeper seems to come from everywhere at once. A hiss spread across many frequencies gives a worker more cues to tell where the truck is. The OSHA letter itself rules only on compliance; it does not require or recommend one type over the other.¹⁰⁶

In the UK, broadband alarms are not a legislative requirement, according to the Considerate Constructors Scheme's best-practice hub (January 2020). ¹⁹⁴ It describes a City of London project, 21 Moorfields, that required broadband-only alarms on all delivery vehicles to cut neighbor disruption and to comply with the City of London's construction code of practice. ¹⁹⁴

What time can construction start?

What you hear: Engines turning over and the first jackhammer hits before your alarm goes off.

In the US there is no national construction-hours rule. Hours come from city and town noise codes, usually a weekday daytime window with stricter limits at night and on weekends, and many cities issue after-hours permits for work that cannot happen in daylight, such as road and rail jobs. Who makes the noise rules covers the specific hours, permits and decibel limits in Boston, New York and other cities, and how to report work outside them.

How loud is a leaf blower?

What you hear: A high, droning whine that rises and falls as the operator sweeps, often with a lower engine growl underneath.

Gas leaf blowers can exceed 100 dBA at the operator's ear and typically measure 65-80 dBA at 50 feet.¹⁹⁵ A 2016 study of North Carolina university groundskeepers found their leaf blower noise exposure averaged 89 dBA and peaked at 106 dBA (distance from the machine not given).⁷² For context on the operator's side, the same Wikipedia article cites the NIOSH recommended exposure limit of 85 dBA over an 8-hour workday.⁷² Hearing risk is covered in What noise does to you.

Do not set the 50-foot numbers against the operator-ear numbers as if they were the same thing. The first is what a neighbor across the yard might get; the second is what the person holding the blower gets.

Are electric leaf blowers quieter?

What you hear: A higher, thinner whir with no engine putter underneath.

In the measurements we found, yes. A 2018 study measured three gas models at 67-77 dBA and four electric models at 57-67 dBA, all at 50 feet - roughly 10 dB lower for electric.¹⁹⁵ Indoors, the electric models' levels were 5-19 dBA lower than gas.¹⁹⁵ A 10 dB drop is about a tenth of the sound energy and is usually heard as roughly half as loud.

Why can you hear a leaf blower from blocks away?

What you hear: A blower you cannot see, somewhere a few streets over, still audible through closed windows.

The answer is in the low end. A 2018 Arup study, as summarized in a December 2020 report to the Village of Scarsdale, New York, found gas blowers have "a significantly greater low frequency sound component" than electric ones.¹⁹⁶ In that study all the tested gas blowers were audible at 800 feet (about 245 meters), while none of the electric ones could be distinguished from background sound at that distance.¹⁹⁶

Low-frequency sound loses less energy to the air and passes through walls and windows more easily than high-frequency sound. A-weighted decibels (dBA, explained in Sound and decibels) also deliberately turn down the low frequencies to match how the ear hears quiet sounds, so a dBA reading can understate how far a low engine drone carries. Two blowers with similar dBA figures at 50 feet can sound very different three houses away.

Who bans leaf blowers, and why is it a fight?

What you hear: Depending on your street, either more blowers or suddenly far fewer.

Leaf blower rules started as noise ordinances. Carmel-by-the-Sea, California banned them as a noise nuisance in 1975 and Beverly Hills followed in 1978.⁷² Newer rules increasingly target gas engines for both noise and air pollution:

• Washington, DC: the Leaf Blower Regulation Amendment Act of 2018 barred gas-powered blowers effective January 1, 2022.⁷²
• California: AB 1346, by Assemblymember Marc Berman, passed in October 2021. It halts the sale of most new gas leaf blowers, mowers and other small off-road engines by 2024 (generators by 2028); existing equipment can still be used, and the bill "barely passed."⁷³
• Seasonal bans: Scarsdale, New York bans gas blowers from June 1 to September 30.¹⁹⁶
• Phase-outs: Portland, Oregon is phasing out gas blowers from 2026, with a ban in 2028.⁷²
• The other direction: Georgia and Texas have limited local governments' power to restrict gas equipment.¹⁹⁵

More than 100 US jurisdictions restrict gas blowers, according to Fine Homebuilding; other counts run higher, and the sources do not agree on one number.¹⁹⁵

The arguments, as the two sides put them. Supporters cite noise, emissions and health: Environment New Jersey's Doug O'Malley said one hour of use pollutes as much as driving a car 1,100 miles, and Montclair, New Jersey ban advocate Jessica Stolzberg said the town became "healthier, cleaner, quieter."⁷⁴ Opponents cite cost and practicality: Rich Goldstein, president of the New Jersey Landscape Contractors Association, said his firm has $150,000 to $200,000 in gas blowers ("What am I supposed to do, throw them in the garbage?"), that battery models are less capable, and that charging means retrofitting trucks; contractors challenged Montclair's ban in court.⁷⁴

What about lawn mowers?

What you hear: A steady engine drone, lower and more constant than a blower.

Mowers usually travel in the same legal bundle as blowers. California's AB 1346 covers gas mowers along with blowers and other small off-road engines.⁷³ New South Wales, Australia, groups mowers and leaf blowers together as garden tools with restricted hours (below).⁶⁸

Electric mowers are quieter, though not silent. In a 2005 newsletter from the Noise Pollution Clearinghouse, an advocacy group, a typical gas mower measured 85 to 90 dBA at the operator (90 to 95 for riding mowers), while electric lawn equipment was usually 80 dBA or less. ¹⁹⁷ At 25 feet, electric mowers measured 60 to 65 dBA and quieter gas mowers 70 to 75 dBA. ¹⁹⁷

In Boston

The city's clearest fingerprint on construction noise is national: the FHWA's standard equipment noise limits come from the Big Dig's specification 721.560, written for the Central Artery/Tunnel project that rebuilt downtown's highways.¹⁹¹

Next door, the Cambridge City Council passed an updated leaf blower ordinance in December 2023. Since March 15, 2025, property owners have not been allowed to use gas blowers on their own property; commercial operators, owners of adjoining parcels totaling two or more acres, city employees and city contractors could keep using them until March 15, 2026. Use of any blower is limited to March 15-June 15 and September 15-December 31, on weekdays 8 a.m.-5 p.m. and Saturdays 9 a.m.-5 p.m., and not on Sundays or legal holidays, apart from set hours on Veterans Day and Indigenous Peoples' Day.¹⁹⁸

The city's leaf blower page says that since March 15, 2026, those remaining users are also limited to electric blowers.¹⁹⁹ A License Commission summary revised February 13, 2026, says all gas leaf blowers "have been banned," but still lists narrow exceptions for municipal contractors: residential street cleaning (while the city does not tow for it), parcels of one acre or larger, and emergencies. The two city sources differ on that point. The summary also caps electric blowers at 65 dBA, as rated by the manufacturer under the ANSI standard.²⁰⁰ Permits, fines and the rules in Brookline and other neighboring towns are in The sound of Boston.

For Boston's construction hours and how to report after-hours work, see Who makes the noise rules and The sound of Boston.

Elsewhere in the world

Outside the US, garden equipment is more often handled with set hours than with bans.

• New South Wales, Australia: power tools and garden tools, including mowers and leaf blowers, may not be heard inside a neighbor's habitable room from 8 p.m. to 7 a.m. on weekdays and 8 p.m. to 8 a.m. on weekends and public holidays.⁶⁸
• Toronto, Canada: the noise bylaw (Chapter 591) prohibits power devices such as lawn equipment from 7 p.m. to 8 a.m., extended to 9 a.m. on weekends and holidays.⁶⁷
• European Union: Directive 2000/14/EC caps the sound power (LWA, not a level at a distance) of new lawnmowers by cutting width - 96 dB for widths up to 50 cm under its first stage - and requires leaf blowers only to carry their guaranteed sound power level next to the CE mark. Article 17 leaves member states free to regulate use in areas they consider sensitive.²⁰¹
• Germany: under the federal equipment and machinery noise ordinance (32. BImSchV), mowers may not run in residential areas on Sundays and public holidays or from 8 p.m. to 7 a.m. on workdays, and leaf blowers are also barred on workdays from 7 to 9 a.m., 1 to 3 p.m. and 5 to 8 p.m., according to Berlin's environment department. The same Berlin page says leaf blowers may be used only from September to February, with exceptions for public services.²⁰²

Report an error in this section