Transit Hub AV Integration: Specifying Displays by Zone

1. Why one spec does not cover a whole hub

Most hub tenders start with a single screen specification and a quantity. That is where the budget goes wrong. A concourse wall, a platform edge and an uncovered bus stop do not share an ambient light level, a temperature range or a cleaning method, so they cannot share a display.

Split the site into zones first. Five cover most projects: the ticket hall and retail concourse, which are conditioned indoor space; the platform, which is semi-outdoor with daylight and wind-blown rain; the shelter or stop, which is a roofed enclosure with open sides; the forecourt and approach roads, which are fully exposed; and the back-of-house control room, which wants a monitor rather than signage.

The parameter that sorts these zones into product lines is usually the operating temperature range. The indoor wall-mount, video wall, bar and floor-standing lines are rated 0 °C to 40 °C. The outdoor IP66 line is rated -20 °C to 50 °C with cold-start capability. A platform that drops below freezing in January cannot use an indoor-rated panel no matter how many nits it carries.

Brightness comes second, and it is the number buyers over-specify. Paying for 5000 nits in a ticket hall buys headroom nobody will use. Dropping 400 cd/m² onto a west-facing platform edge makes it unreadable from April to September.

2. Brightness by zone: the number the screen has to beat

Set brightness against the ambient light the panel has to beat, not against a catalogue maximum. Direct summer sun is around 100,000 lux. An indoor concourse is a few hundred. That gap of roughly two orders of magnitude is why one fleet-wide number never works.

Indoor zones are the easy case. The LCD video wall line runs 400 cd/m² with 700 cd/m² optional, and the wall-mount line covers 300 to 500 cd/m² across 32 to 98 inches. Both are enough for gate information, wayfinding walls and concourse retail.

A roofed shelter with open sides is the middle case. Daylight reaches the panel but direct sun rarely does. 1500 to 2500 nits covers it, and this is where most stop and shelter deployments land.

Fully exposed positions, meaning platform edges without a canopy, forecourts and roadside stops in high-sun regions, need 3000 to 5000 nits. The outdoor IP66 line is offered at 1500, 2500, 4000 and 5000 nits from 32 to 86 inches, rated -20 °C to 50 °C.

At those levels auto-dimming is not an option, it is a requirement. A 5000 nit panel left at full output after dark is a glare complaint and a power bill. The failure mode is the threshold: set the step too late and the screen is unreadable through the dawn and dusk peaks, which is exactly when passenger flow is highest. Ask for the lux threshold and the dimming curve in the quotation, not just a line saying dimming is supported.

Brightness does not fix glare. Low sun at a shallow angle puts a specular reflection on the cover glass that no amount of output will punch through. Anti-reflective treatment and optical bonding, which removes the internal air gap, are the measures that work there.

3. Enclosure, impact and the standards behind them

Water and dust protection is defined in IEC 60529. The second digit is the water test: a 5 covers low-pressure jets from a 6.3 mm nozzle, a 6 covers powerful jets from a 12.5 mm nozzle at roughly eight times the flow rate. Both are dust-tight in the ratings that matter here.

IP65 is enough under a roof that is cleaned by hand. IP66 is required where the unit is pressure washed or fully exposed. The cleaning regime decides it: if the operator washes shelters with a hose, the rating follows the hose.

Impact resistance is a separate standard. IK levels are defined in IEC 62262 and are not part of an IP code. Public-facing screens on an unsupervised site need tempered glass and an IK level agreed with the operator, because the IP rating says nothing about a kicked panel.

What the rating leaves out matters as much as what it covers. IEC 60529 tests solids and water only. It says nothing about heat rejection, UV stability, corrosion of the fixings or how long the seals last. Ask for the test report that covers the exact enclosure being quoted rather than a family certificate.

4. Legibility: how much text a screen can carry

Arrival boards fail on legibility more often than on brightness, and the binding limit is geometry rather than panel quality. Snellen 20/20 acuity corresponds to a minimum angle of resolution of 5 arcminutes, so the threshold character height at distance d is d multiplied by tan(5 arcminutes), about 0.00145 d. At 20 m that threshold is 29 mm.

Wayfinding practice applies a safety factor over that threshold, typically 3 to 5 times, giving a design character height of 87 to 145 mm at 20 m. That range is the source of the d/230 to d/138 rules of thumb.

Put it on a real panel. A 55 inch 16:9 screen has an active area near 1218 by 685 mm, so a 1920 by 1080 panel has a pixel pitch close to 0.63 mm. An 87 mm character is about 137 pixels tall, which is 12.7 percent of screen height. The screen therefore carries roughly seven lines of legible text at the 3 times factor, and fewer than five at 5 times.

That is the constraint that decides the format. An arrival board showing five services plus a header and a clock is already at the limit on one 55 inch screen at 20 m. If the content needs more lines, either shorten the list and cycle it, or move to a taller portrait panel or a stacked pair. Portrait orientation suits arrival strips because it buys line count rather than width.

Platform arrival strips usually sit along the canopy edge where there is no depth for a 55 inch cabinet. The LCD bar line runs 23 to 58.5 inches in stretched formats and mounts into that gap at 400 to 700 cd/m². Confirm whether sun reaches the panel there, because if it does the bar moves to the outdoor line.

Confirm the character height against the accessibility standard that applies to the authority, and settle the mounting height and viewing cone with the architect before the enclosure is ordered.

5. Mounting, service access and what fails in year two

Mounting is decided by the wall, not the screen. The wall-mount line uses VESA patterns from 200 by 200 mm to 600 by 400 mm with a concealed cable channel and a lockable bezel option for unsupervised positions. Confirm the substrate carries the load before the size is fixed: a 98 inch panel on a plasterboard partition is a structural question, not a display question.

The parts that fail are not the parts buyers worry about. Water enters at the cable gland or the door seal, not through the glass. Condensation forms behind the cover glass when the panel cools faster than the air inside, and optical bonding removes the gap where it forms.

Service access is the item most often missing from the tender. Ask how the unit opens, whether the media player can be reached without breaking the enclosure seal, and what the seal and filter check interval is. A screen that needs a lift and two technicians to reboot is a screen that stays dark.

Freestanding totems and interactive wayfinding follow the same zone logic. The floor-standing line covers 32 to 65 inches with a metal housing and tempered glass front, and the touch kiosk line covers 32 to 65 inches where passengers need to query rather than read.

6. Network, CMS and time: the parts that are not the screen

On an unmanned network the screen is the easy part. The management layer decides whether a fault costs one screen-hour or a week of dark panels.

Four requirements are worth writing into the specification. Remote monitoring with a heartbeat, so the operator knows a screen is down before a passenger reports it. Automatic recovery, meaning the player reboots itself or the CMS re-pushes content without a site visit. Local store-and-forward, so the panel keeps playing cached content when the link drops instead of going blank. And time synchronisation over NTP.

Time is the one that gets missed. An arrival board with a five-minute drift is worse than a dark screen, because passengers act on it. Specify the NTP source, a drift alarm, and a defined fallback display when the feed is stale.

Content structure matters just as much. Group screens by zone so a platform group can carry service disruption messages while concourse retail keeps its schedule. For multi-face totems, confirm whether the faces play in synchronisation or independently, and state which one you want.

On power, size the circuits from the nameplate rating of the model being quoted and require it in the tender response. Do not size from an assumed figure, and do not assume two models in the same series draw the same.

7. What this article does not cover

Onboard rolling stock is a different regime. Electronic equipment on trains falls under EN 50155 and fire safety under EN 45545, and vehicle displays are engineered to vibration and voltage transient requirements that fixed infrastructure screens are not. Nothing here applies to a screen mounted inside a train or a bus.

Platform screen door integrated displays, passenger information system protocol work and public address interfaces are integration scope. They need an interface agreement between the display supplier, the PIS vendor and the operator, and they belong in the integration package rather than the display tender.

Accessibility compliance is jurisdiction specific. Character contrast, mounting height, audible equivalents and tactile requirements are set by the authority having jurisdiction and should be confirmed before the enclosure is tooled.

8. What to put in the RFQ

Send these eight and you will get quotes you can actually compare against each other.

1. Zone map. Which screens sit in conditioned indoor space, which under a roof, and which in full exposure. This sets the product line.
2. Brightness per zone. State the target in nits and the ambient condition it was chosen for, not one fleet-wide number.
3. Enclosure and impact. IP level with the IEC 60529 test report for the exact enclosure, plus the IK level under IEC 62262.
4. Operating temperature. The measured site range including the coldest start. Ask for the model rating, not the series rating.
5. Viewing distance and content. Distance to the furthest reader and the number of text lines the screen must carry. This sets size and orientation.
6. Management. Remote monitoring, automatic recovery, local cache behaviour when the link drops, and the NTP source.
7. Service. How the unit opens, seal and filter intervals, and the spare pool agreed against acceptable downtime.
8. Quantity, destination and compliance. The last one decides which files are needed for the target market.

One practical point to finish on. Screens from a single supplier across all zones share a CMS, a spare parts pool and a service procedure. Splitting the tender across three vendors to save a small amount per unit usually costs more in year two. The transit signage line shows how the zone split maps onto models.

Transit hub zones against display specification

Zone	Ambient	Brightness	Enclosure	Operating range	Line
Ticket hall and concourse	Conditioned indoor	300 to 500 cd/m²	Indoor housing	0 °C to 40 °C	Wall-mount, floor-standing
Concourse wayfinding wall	Conditioned indoor, long sight lines	400 cd/m², 700 optional	Indoor housing	0 °C to 40 °C	LCD video wall
Canopy arrival strip	Sheltered, no direct sun	400 to 700 cd/m²	Indoor housing	0 °C to 40 °C	LCD bar
Platform under canopy	Daylight, wind-blown rain	1500 to 2500 nits	IP65	-20 °C to 50 °C	Outdoor IP66
Platform edge, open	Direct sun	3000 to 5000 nits	IP66	-20 °C to 50 °C	Outdoor IP66
Bus shelter, roofed	Reflected daylight, open sides	1500 to 2500 nits	IP65	-20 °C to 50 °C	Outdoor IP66
Forecourt and approach	Full exposure, hose cleaning	3000 to 5000 nits	IP66	-20 °C to 50 °C	Outdoor IP66

Frequently Asked Questions