08Trains, subways and the screech on the curve

The short version: In the US, a federal rule requires locomotive horns at public grade crossings, at 96 to 110 dB(A) measured 100 feet ahead of the locomotive, in a long-long-short-long pattern, and the only way to silence them is a quiet zone backed by extra safety measures. Underground, the loudest sound is often wheel squeal on tight curves, which can reach about 100 dB(A) at 10 m; New York City studies have recorded subway platform peaks of 102 to 106 dBA. Lubrication, water spray and other fixes help at some sites and not at others.

How loud is a train horn, and why do trains honk at night?

What you hear: Two long blasts, a short one and a final long one, held until the train reaches the crossing, at any hour.

The Federal Railroad Administration (FRA) Train Horn Rule, at 49 CFR Part 222, requires locomotive engineers to begin sounding the horn 15 to 20 seconds before reaching a public grade crossing, and for fast trains no more than a quarter mile ahead. The pattern is two long, one short and one long, repeated or prolonged until the locomotive occupies the crossing.¹⁴⁵ The rule does not change at night, which is why horns are often most noticeable then: the horn is the same, but the background is quieter.

The horn must be at least 96 dB(A) and no more than 110 dB(A), measured 100 feet ahead as described below. The final rule moved the measurement microphone to 15 feet above the top of the rail, up from 4 feet.¹⁴⁶

Dates for the rule are often given inconsistently. FRA published the final rule on April 27, 2005 (70 FR 21844), and it took effect June 24, 2005.¹⁴⁶¹⁴⁷ FRA then amended it in a final rule responding to petitions for reconsideration, published August 17, 2006 (71 FR 47614) and effective September 18, 2006.¹⁴⁷ FRA's current web page describes the rule as "effective August 17, 2006," which is the publication date of those amendments, not their effective date.¹⁴⁵¹⁴⁷

Under 49 CFR 229.129, the 96 to 110 dB(A) range applies at 100 feet forward of the locomotive in its direction of travel, with the test microphone 15 feet above the top of the rail for standard horns and 4 feet for cab-mounted or low-mounted horns.¹⁴⁸

How does a town get a train quiet zone?

What you hear: Trains rolling through crossings with bells and gates but no horn.

A quiet zone is a stretch of line where trains do not routinely sound horns at crossings. Only a public authority that controls the crossings - typically a city or town - can create one; a railroad or a group of neighbors cannot.¹⁴⁵ The authority has to add safety measures that make up for the lost warning, and a quiet zone is generally at least half a mile long.¹⁴⁶ Whistle bans that existed before the rule could be grandfathered under certain conditions.¹⁴⁶

An alternative is a wayside horn: a horn mounted at a gated crossing and aimed down the road at drivers, which can substitute for the train horn and covers a much smaller area.¹⁴⁶ Even inside a quiet zone, engineers may still sound the horn in an emergency, such as a person or vehicle on the tracks.¹⁴⁵

Nationally, the Government Accountability Office counted 570 new quiet zones - those established under the rule - in 42 states as of June 2017.¹⁴⁹

Other countries handle this differently. In Canada, the Canadian Rail Operating Rules require trains to whistle at every public grade crossing. A municipality can stop it by assessing the crossings with the railway against section 104 of the Grade Crossings Regulations, giving public notice and passing a council resolution; the railway then issues instructions to stop whistling and must confirm in writing within 30 days after it stops, and a Transport Canada inspector can order whistling to resume if the crossings are not maintained.¹⁵⁰

In Great Britain, drivers sound the horn at about 1,600 crossings marked with whistle boards. Network Rail's Night Time Quiet Period, introduced in 2007, limits horn use there to emergencies at night; in December 2016 it was shortened from 11 p.m.-7 a.m. to 11:59 p.m.-6 a.m., after a 2015 RSSB study found that 64% of near misses during the quiet period happened in its shoulder hours.¹⁵¹

How many people hear rail noise?

In Europe, the European Environment Agency counted 19 million people exposed to railway noise at or above 55 dB Lden in 2012, second only to road traffic at about 100 million (see traffic).¹¹⁷ Lden is a 24-hour average with penalties for evening and night sound. The EEA's 2025 report, using 2022 data, put the rail figure at about 18 million.²

How loud is the subway?

What you hear: A roar as the train enters the station, brake hiss, and on some lines a high shriek that makes people cover their ears.

Two New York City studies give the clearest numbers. A 2006 pilot survey by Robyn Gershon and colleagues, reported in the Journal of Urban Health, found an average maximum of 94 dBA on subway platforms, 95 dBA inside subway cars and 84 dBA at bus stops. The highest platform reading was 106 dBA, and more than 1 in 10 platform readings were above 100 dBA.¹⁵²

A 2009 study by Richard Neitzel and colleagues in the American Journal of Public Health measured an average of 80.4 dBA on the subway, the highest of the transit modes it measured (Metro-North commuter rail averaged 75.2 dBA). The maximum was 102.1 dBA on a platform, and about half of the subway maximum readings were above 90 dBA.¹⁵³ The University of Washington's write-up compared these with EPA and WHO guidance of 70 dBA averaged over 24 hours to protect hearing.¹⁵³

Keep the metrics apart: the 80.4 dBA figure is an average over a ride, while the 94, 102.1 and 106 dBA figures are maximums, the loudest moment of a reading. A brief peak and a long average describe different things and are not interchangeable. What those levels mean for hearing is covered in the health section.

For London, a 2015 paper in the Proceedings of the Institute of Acoustics by researchers at London South Bank University measured whole Underground journeys, including platform waits, walking and interchanges, with a shoulder-worn dosimeter. Journey averages ran from 84.3 to 85.5 dB LAeq, and a 12-minute seated stretch of the Central line averaged 90.9 dB LAeq. The highest C-weighted peak was 131.1 dB LCpeak, a peak metric that cannot be compared with the averages.¹⁵⁴ The paper cites earlier work finding platform levels often above 80 dB LAeq while a train arrived, boarded and left.¹⁵⁴

Why do trains screech on curves?

What you hear: A piercing, almost musical squeal as a train rounds a tight bend, sometimes rising and falling in pitch.

A rail vehicle's wheels are fixed to axles, so on a tight curve they cannot steer perfectly along the rail. The wheels slip sideways across the railhead, and that stick-slip motion makes the wheel ring like a bowed string. A 2005 report for the International Union of Railways (UIC) lists three mechanisms: lateral creep (the sideways slip, which it calls the most important), flange rubbing, and slip along the direction of travel. Squeal frequencies run up to 10,000 Hz, and levels reach about 100 dB(A) at 10 m.¹⁵⁵

Wheel squeal is separate from the general roar of a train, which comes from wheels rolling on rails and from the motors. The squeal is a tone, concentrated at a few high frequencies, and it is why the same train sounds fine on straight track and painful on one particular curve.

How bad a given curve is depends on its radius, the wheel and rail profiles, the climate and maintenance, so results from one site rarely transfer neatly to another.¹⁵⁵

What fixes wheel squeal?

What you hear: The same curve that shrieked last month is quieter now, or worse.

The UIC report reviewed trials across European railways, and the results were mixed:¹⁵⁵

L10, L20 and L50 are statistical levels: the level exceeded 10%, 20% or 50% of the time during the measurement. The table's numbers come from different sites and metrics, so they show which fixes worked where, not a ranking.

Rail grinding, which reshapes the railhead, is another maintenance option. Its best-documented effect is on rolling noise rather than squeal: after 2016 grinding campaigns on Dublin's Luas light rail, Transport Infrastructure Ireland measured pass-by reductions of 4.0 to 11.7 dB LAeq,Tp at two sites, and the larger gain shrank by about 1 dB a month as corrugation returned.¹⁵⁶ That study measured rolling noise, not curve squeal.

In Boston: the Green Line at Boylston

What you hear: An inbound Green Line train shrieking as it turns from under Boylston Street onto Tremont.

The inbound turn at Boylston station is the squeal spot Boston riders cite most. In a 2017 WBUR report, an engineer from the acoustics firm Acentech called it "one of the sharpest turns in North America." The MBTA then had 13 greaser units on the Green Line with six more coming, and was testing graphite flange-stick lubricators. The curve's radius cannot be widened, because the tunnel is too old to rebuild around it.¹⁵⁷ For how a city's rail system works more broadly, see How a City Works: transit.

The Green Line has been a test bed for this before. A 1982 US Department of Transportation noise test found that a light rail vehicle on resilient wheels was about 10 dB quieter inside the car than a PCC streetcar on solid steel wheels, and found no significant difference in wayside noise on straight track between the two resilient wheel designs tested.¹⁵⁸ The sound of Boston covers more of the city's noise.

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