11The gear on traffic signal poles

The short version: A signal pole carries much more than red, yellow and green: the yellow-edged backplates, the blinking left-turn arrow, the ticking push button, the small blue light and the assortment of cameras each have a specific job. Backplates make signals easier to see, and many cameras on signal arms detect waiting vehicles rather than record drivers.¹⁸³¹⁸⁴ Mid-block, some US crossings use beacons that stay dark until someone pushes a button. Elsewhere, UK crossings have animal names, Berlin's walking man wears a hat, and in Japan the green light is called blue.

Why do some traffic lights have a yellow border?

What you see: Signal lights set in a black rectangular frame with a thin, bright yellow outline that glows in headlights.

The black frame is a backplate. It gives the lit lenses contrast against a bright sky. The yellow strip, 1 to 3 inches (2.5-7.5 cm) wide, is retroreflective, so it shines back at drivers at night and outlines a dark signal during a power outage.¹⁸³ The Federal Highway Administration (FHWA) lists backplates with retroreflective borders as a Proven Safety Countermeasure and credits them with a 15% reduction in total crashes (CMF ID 1410).¹⁸³

FHWA says the borders help older drivers and drivers with color-vision deficiency, and that agencies can retrofit existing backplates cheaply with reflective tape. The trade-off is that a backplate adds wind load to the mast arm.¹⁸³

What does a flashing yellow arrow mean?

What you see: A left-turn signal with four lights stacked vertically, where the yellow arrow blinks.

A flashing yellow arrow means a permissive left turn: you may turn after yielding to oncoming traffic and pedestrians.¹⁸⁵¹⁸⁶ In Wikipedia's wording, it allows traffic to "cautiously enter the intersection" while yielding.¹⁸⁶ A solid green arrow, when the same head shows one, means the turn is protected and oncoming traffic is stopped.

The flashing yellow arrow was formally authorized in the US federal Manual on Uniform Traffic Control Devices (MUTCD) in 2009, and Minnesota followed in 2011. Drivers read it well: in a University of Minnesota survey, about 94% of respondents understood it without a sign and 96% with one.¹⁸⁵

What do the countdown numbers and push buttons do?

What you see: A box showing a white walking person, an orange hand and a number counting down. A button sits on the pole nearby.

The countdown shows the seconds left before the signal changes. In the US and Canada, countdown timers usually accompany the flashing hand, and in the UK they run during the "blackout" period when no pedestrian figure is lit.¹⁸⁶ Studies show improved pedestrian compliance with mixed results, and no significant change in drivers running red lights.¹⁸⁶

The push button tells the controller that someone is waiting. Cambridge, Massachusetts tells pedestrians that at its signals with buttons, the WALK phase is skipped if nobody presses, while at intersections with no buttons the WALK comes on every cycle.¹⁸⁷

Not every button is wired that way. The Boston Globe reported in July 2017 that the vast majority of buttons in downtown Boston did nothing, because the signals there run on a fixed schedule with a regular WALK; some worked only overnight, and buttons in outlying neighborhoods often still worked by day.¹⁸⁸ The Globe described no visible way to tell a working button from a dead one, and the city did not provide a list of affected intersections.¹⁸⁸

Why does the crosswalk button tick or vibrate?

What you see: A larger push button with a raised arrow and a small speaker, ticking steadily about once a second. When the walk signal comes on, it rattles rapidly or speaks, and the arrow vibrates.

This is an accessible pedestrian signal (APS), built for blind and low-vision pedestrians. The steady tick is the locator tone. It repeats once per second and lasts at most 0.15 seconds, so it is not mistaken for a backup alarm.¹⁸⁹ It helps people find the button and line up with the crossing.

The raised arrow points parallel to the crosswalk. During WALK it vibrates, which works at noisy intersections and for deafblind pedestrians. The audible WALK may be a rapid repetition of the locator tone, a different tone, or speech.¹⁸⁹

The rapid "machine-gun" tick is the sound guidelines recommend. Older cuckoo-and-chirp signals confused people and could be mimicked by mockingbirds. Pressing and holding the button often plays the street name, and speech messages are preferred when two buttons are less than 10 ft (3 m) apart, so it is clear which crossing is getting the WALK.¹⁹⁰

In Boston, the city's APS specification calls for a 0.15-second locator tone at about one per second with automatic volume adjustment; a latching LED, tone and vibration when the button is pressed; optional speech WALK messages; a 5 x 7 inch (13 x 18 cm) MUTCD R10-3 sign with Braille and a matching arrow; messages programmable over Bluetooth; and operation from -25 to 165 F (about -32 to 74 C).¹⁹¹¹⁹²

What is the blue light on top of a traffic light?

What you see: A small blue light, sometimes white, on top of, under or behind a signal head, or on the mast arm. It is lit whenever the signal is red.

It is a red-light confirmation light, an enforcement aid and not a camera. The light turns on with the red, so a police officer parked downstream or across the intersection can see that a driver entered on red without being able to see the signal face. Bismarck, North Dakota, which uses them, says they let officers see violations from a safe position and that "red-light confirmation lights do not use automated photography."¹⁹³

Mounting varies: Bismarck describes lights on the top, bottom or rear of a signal head.¹⁹³ Hudson, New Hampshire installed one on March 16, 2020, the first in that state, and it shows blue when the signal is red and white when inactive.¹⁹⁴

They appear in scattered US cities. As of October 2026 this guide found no record of them in Massachusetts, the UK or the EU.

What is the small sensor pointed down the road? (emergency preemption)

What you see: A small cylindrical or bullet-shaped sensor, often with a dark lens, on the mast arm and aimed at approaching traffic.

This is likely an emergency preemption detector, a receiver that lets fire trucks and some other vehicles request a green light. Optical sensors respond to strobes flashing at a very high rate, and some respond only to specific patterns. Opticom, one widely used system, "combines GPS and Infrared technology."¹⁹⁵

The vehicle's emitter sends the coded signal, the detector passes it to the signal cabinet, and the controller ends the conflicting phase early. The sister guide covers how emergency calls turn into a dispatched truck in How a City Works: 911.

Some cities add a confirmation light for the emergency driver. Bismarck, North Dakota uses white lights: dark most of the time, steady white when the system has received the vehicle's infrared request, and flashing white when it is already serving a call from another approach.¹⁹⁶ The blue light described above, by contrast, comes on with every red, whether or not an emergency vehicle is near.¹⁹³ Colors are not uniform everywhere: Hudson, New Hampshire's enforcement light shows white when inactive.¹⁹⁴

What are the cameras on traffic lights for?

What you see: Assorted small cameras, domes and boxes on or above the signal arms, and sometimes a larger box on its own pole near the stop line.

Many devices on signal arms are vehicle detection: they tell the controller that a car is waiting. Bloomington, Minnesota describes its video detection cameras as mounted high on the signal structure with a fixed focus and no pan or zoom. A processor watches predefined zones and places a call to the controller. The city says there is "no constant surveillance or archiving," though some diagnostic clips may be kept briefly.¹⁸⁴

The older method is the inductive loop, a wire loop saw-cut a few inches into the pavement; a vehicle above it changes the inductance, and the signal cabinet on the corner receives the call.¹⁸⁴

LegalClarity, a legal-information site, offers rough visual cues for the other kinds:¹⁹⁷

These are general cues from a secondary source, not a manufacturer standard, and look-alikes exist. Camera enforcement and ALPR are debated; this guide stays neutral and describes only how to tell the devices apart.

In Massachusetts, camera ticketing has needed new state law. Senate bill S.2344 of 2025, "An Act relative to traffic regulation using road safety cameras," was reported favorably by the Joint Committee on Transportation on July 7, 2025 and sent to Senate Ways and Means.¹⁹⁸ Senate bill S.3225 would create an automated road safety enforcement program for speed only, in school, work and designated safety zones, with a warning first, fines of $25 or $100, at most one camera per 5,000 residents, and a ban on facial recognition.¹⁹⁹

Axios Boston reported on August 3, 2026 that the Senate had passed speed-camera authority as an amendment to an economic development bill, which would make Massachusetts allow them for the first time, while the House had not acted. Gov. Maura Healey has long pushed for the measure, and critics argue cameras raise privacy and racial-equity concerns or serve as a revenue tool.²⁰⁰ As of October 2026, this guide had not confirmed a later outcome.

The sister guide explains controllers, phases and detection in How a City Works: Traffic lights.

What is a HAWK signal?

What you see: Over a mid-block crosswalk, a signal head with two red lights side by side above one yellow. It is dark most of the time.

This is a pedestrian hybrid beacon (PHB), often called a HAWK. It rests dark until a pedestrian pushes the button. Then it runs: brief flashing yellow, steady yellow, steady red with WALK for pedestrians, flashing hand, alternating flashing red, and back to dark. It is used only with a marked crosswalk and appears in Chapter 4F of the US MUTCD. FHWA cites reductions of up to 69% in pedestrian crashes and 29% in total crashes.²⁰¹

The HAWK was developed in Tucson, Arizona, which had more than 60 of them at the time of FHWA's evaluation. A before-and-after study of 21 sites found 29% fewer total crashes, 69% fewer pedestrian crashes and 15% fewer severe crashes, though the severe-crash change was not statistically significant.²⁰²

During the alternating flashing red, FHWA says drivers may proceed across the crosswalk "after coming to a complete stop" and "if it is safe to do so." Because drivers were seen waiting through the whole flashing red even with the crosswalk clear, FHWA allows an optional R10-23a word sign, CROSSWALK, STOP ON RED, PROCEED ON FLASHING RED WHEN CLEAR, in place of the standard symbolic CROSSWALK, STOP ON RED (R10-23) sign required by Section 4F.02 of the 2009 MUTCD.²⁰³

What are the flashing yellow lights at a crosswalk?

What you see: Two small rectangular yellow LED bars under a pedestrian crossing sign that strobe in a fast left-right pattern after someone presses a button.

This is a rectangular rapid flashing beacon (RRFB), used at crosswalks without a traffic signal. It stays dark until activated by a push button or by passive video or radar detection, then flashes in an alternating high-frequency pattern.²⁰⁴

It is an FHWA Proven Safety Countermeasure, credited with up to 47% fewer pedestrian crashes and up to 98% more drivers yielding (CMF ID 9024). It works best on multilane roads with speeds under 40 mph (64 km/h). In the US it appears in Chapter 4L of the MUTCD 11th edition (2023).²⁰⁴

Unlike a HAWK, an RRFB never shows red. It warns drivers that someone is crossing.

What are the rows of blue bikes and the kiosk? (Bluebikes in Boston)

What you see: A row of docks holding blue bicycles, a tall kiosk with a solar panel and a map, or newer freestanding "pillar" docks, often beside a signalized corner.

This is a docked bike-share station. Boston's system launched as Hubway on July 28, 2011 and was renamed Bluebikes on May 9, 2018 under a sponsorship with Blue Cross Blue Shield of Massachusetts. Its bikes and docks come from PBSC, with newer docks from 8D Technologies, and the station kiosk is solar-powered. It had more than 400 stations by 2023.²⁰⁵

Bluebikes is jointly owned by 13 municipalities: Arlington, Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Medford, Newton, Revere, Salem, Somerville and Watertown. The newer Pillar docks are independently powered by solar panels, with an optional grid connection for charging e-bikes. Boston began a 100-station expansion in September 2024.²⁰⁶

Solar power is why most stations can go in without a grid hookup.

A short history of the traffic light

What you see: The three-color signal, everywhere.

The first traffic signals were police-operated semaphores with red and green night lights in London's Parliament Square in 1868. Lester Wire built an electric traffic light in Salt Lake City in 1912, and the American Traffic Signal Co. installed an electric signal in Cleveland, Ohio in August 1914.¹⁸⁶

Elsewhere in the world

Why does the UK show red and amber together?

What you see: Red, then red and amber lit together, then green, then amber alone.

In the UK, red means stop; red and amber together mean prepare to go but do not proceed; green means go if the way is clear; and amber alone means stop unless it is unsafe to do so.¹⁸⁶ US signals skip the red-and-amber step.

What is the difference between zebra, pelican, puffin, toucan and pegasus crossings?

What you see: UK crossings with animal names. Some have striped poles topped with flashing orange globes. Some show a red or green figure across the road, others on the button box.

All rows: Carbuyer.²⁰⁷

At a puffin, then, you look at the button box, not across the road, to see when to go.

What is the Berlin traffic light man called?

What you see: In Berlin and eastern Germany, a stocky pedestrian figure in a hat, striding when green and standing with arms out when red.

This is the Ampelmännchen, "little traffic light man." Traffic psychologist Karl Peglau presented the design on October 13, 1961, meant to be clearer to children. Introduction was delayed to 1963, and the first successful testing came on Unter den Linden in 1969. The hat raised worries that the figure looked "bourgeois."²⁰⁸

After reunification the figures began to be removed. Designer Markus Heckhausen started making lamps from old units in 1995, and the "Save the Ampelmännchen!" committee formed in 1997 to bring the figure back.²⁰⁸

Why does Japan call green lights blue?

What you see: In Japan, the go light looks distinctly blue-green, and people call it ao, blue.

Japanese signals use 青 (ao), usually translated as blue, though the light is green, a holdover from older Japanese usage. In 1973 the go light was decreed to be "the bluest possible shade of green," keeping an internationally recognizable green while matching the word.¹⁸⁶

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