Transit Passenger Display

Overview

Transit passenger displays are information screens installed in bus shelters, train stations, and ferry terminals to show real-time vehicle arrivals, service alerts, and journey planning information. These displays pull data from the transit agency's GTFS (General Transit Feed Specification) server via LTE/GPS, updating arrivals every 30 seconds. Unlike traditional static route maps, the display is dynamic and live, showing which buses are delayed, rerouted, or canceled.

The display combines a sunlight-readable LCD panel with an embedded Linux computer, LTE modem, backup battery, and heater to handle outdoor temperature extremes and power outages. Shelters are often unheated and have no dedicated power, so the display must be self-contained and resilient.

How it works

The display controller (an ARM Cortex-A72 computer) boots from eMMC storage and fetches the transit agency's GTFS feed over LTE. This includes vehicle positions, scheduled arrivals, service advisories, and real-time delay estimates. The controller parses this feed and renders a list of the next 4–6 arrivals on the LCD, sorted by time, color-coded by route.

LTE connectivity is primary; GPS is used for time-keeping and geofencing (ensuring the display shows only routes serving the current stop). Ethernet port allows hardwired connectivity in fixed shelters with power outlets.

The LCD panel is edge-lit with four white LEDs along its edges. A brightness controller reads an ambient light sensor and modulates the backlight PWM to 80% in daylight (1500 nits) and 20% at night (300 nits). This prevents washout and reduces power draw by 60% at night.

The power system accepts 120 VAC from shelter mains or a dedicated circuit. A 30 A charger converts this to 48 VDC and floats the battery at full charge. The 48V 12 Ah LiFePO4 battery provides 4+ hours of runtime if mains is lost. An inverter can supply backup AC if needed for heated shelters.

The heater is critical in cold climates. Liquid crystal displays become sluggish below 0°C and inoperable below -20°C. A 500 W electric heater with thermostat maintains the cabinet interior at 5°C minimum. In -20°C weather, this consumes about 150 W continuously, within the battery runtime budget.

Outdoor durability

The cabinet is sealed to IP66 (complete dust protection, water jets at any angle). Seals are gaskets around the door and cable ports. A desiccant breather vent allows pressure equalization without admitting moisture, silica gel absorbs condensation from air entering during temperature cycling.

The antenna is mounted atop the cabinet on a ±5 dBi MIMO array tuned for LTE (700–800 MHz) and GPS (1575 MHz). In dense urban canyons, LTE-M and NB-IoT provide fallback connectivity with lower bandwidth and longer range.

The tempered glass window has anti-reflective (AR) coating to reduce glare. Uncoated glass reflects 4% at the air-glass interface; AR coating brings this to 0.5%, allowing the 1500 nit display to be readable even in bright sunlight without excessive reflection of the sky.

Data sources

Feeds are pulled from the GTFS server, typically hosted by the transit agency on a private network or cloud. The display controller caches GTFS data locally and refreshes every 30–60 seconds. If LTE is lost, the display falls back to showing cached data (arrivals from the previous fetch) for up to 30 minutes. A status icon alerts riders that information may be stale.

Custom APIs can feed service alerts, emergency announcements, and wayfinding directions alongside the GTFS arrivals. Some installations integrate passenger counting sensors to show occupancy ("Bus 42 arriving, high capacity").

Maintenance

Displays are field-upgradeable via USB. The controller accepts a thumb drive with new OS images or firmware updates. SIM cards are removable, allowing carrier changes or plan upgrades without opening the cabinet. Battery packs are modular and can be swapped in 5 minutes if degradation occurs (after 3–5 years of daily cycles).

Brightness degradation is typically 10–15% after 50,000 operating hours (5+ years). Backlight LEDs can be replaced by removing the bezel.