Audi Traffic Light Information — V2I without a roadside radio.
Audi Traffic Light Information is the longest-running production vehicle-to-infrastructure service in the United States, and it has never used a roadside radio. Signal state travels from the municipal traffic management systems, through an aggregator and a backend, and reaches the car over 4G.
It earns a study twice over: the same automotive group ships direct 5.9 GHz communication in Europe, and a 2023 service bulletin filed with a United States regulator records precisely how a cloud-mediated feature dies.
Infrastructure-sourced V2X, delivered over cellular. Not direct V2I.
Audi Traffic Light Information is the longest-running production vehicle-to-infrastructure service in the United States, and it has never used a roadside radio. Signal state travels from the traffic management systems that operate the intersections, through an aggregator and the manufacturer's backend, and reaches the car over its own 4G connection under a connected-services subscription.
It earns a study for two reasons. It is the same automotive group that ships direct 5.9 GHz communication in Europe choosing an entirely different architecture for the same broad problem in a different market. And it is the only deployment in this section for which a manufacturer has filed a regulator-visible document recording precisely what a back-end compatibility lifetime costs, and which cars it cost it to.
| Field | Verified position |
|---|---|
| Category | Infrastructure-sourced V2X, cloud-delivered |
| First production | 2016, launched in Las Vegas |
| Markets | United States, later extended in Europe |
| Path | Traffic management system to a signal-data aggregator to the manufacturer backend, then over 4G to the vehicle |
| Direct radio | None. No DSRC, no C-V2X PC5, no roadside unit. |
| Functions | Time-to-green; from February 2019, a green-light optimised speed advisory |
| Requirements | A connected-services subscription, an in-vehicle cellular connection and a satellite position fix |
| Scale | Audi states its data partner collects at more than 20,500 intersections across 96 agencies and cities in 26 US metropolitan areas. The article carries no publication date. |
| Current availability | Audi states TLI is offered with an Audi connect PRIME subscription in most Audi vehicles on sale today. No per-model or per-city list is published. |
| Service continuity | Withdrawn from one early population. See section 4. |
Signal timing in the instrument cluster, from 2016.
Audi launched Traffic Light Information in the United States in 2016, in partnership with a company that aggregates and predicts signal state from municipal traffic management systems. Approaching an instrumented intersection, an equipped and subscribed vehicle displays the time remaining until the signal turns green.
In February 2019 the service added a green-light optimised speed advisory: a recommended speed calculated from the signal timing and the vehicle's position, so that the driver arrives during a green interval rather than stopping. Audi described itself as the first manufacturer to launch that function in the United States. Coverage grew through metropolitan areas including Dallas, Houston, Denver, Gainesville, Orlando, Kansas City, Las Vegas, Los Angeles, San Francisco, New York City, Phoenix, Portland, Washington DC and northern Virginia. Audi’s own current statement is that its data partner collects at more than 20,500 intersections across 96 agencies and cities in 26 US metropolitan areas, and that TLI is offered with an Audi connect PRIME subscription in most Audi vehicles on sale today. That article carries no publication date, and Audi publishes no per-model or per-city list, so this study states current coverage exactly as Audi states it and goes no further.
These are the same functions — signal phase and timing, and speed advisory — that the European and Chinese direct-radio programmes deliver through roadside units on 5.9 GHz. Audi delivered them years earlier, over cellular, with no roadside hardware at all.
The signal controller never talks to the car.
Municipal traffic management system
The system that already operates the signals holds the phase and timing state.
Signal-data partner
Ingests many municipal systems, normalises them, and predicts the time to the next phase change.
Manufacturer backend
Serves the data to subscribed vehicles. This node is the one that later ends the story.
Cellular connection
Requires an in-vehicle data connection and a connected-services subscription.
Vehicle
Time-to-green, and a speed recommendation.
Set against the direct alternative, the trade is stark and instructive. A roadside-unit deployment requires the road authority to procure, install, power, connect, secure and maintain a radio at every instrumented intersection. This architecture requires the road authority to do nothing it was not already doing: it already runs a traffic management system, and the data is taken from there. That is why it scaled to thousands of intersections in a market that has almost no roadside V2X radio estate.
The cost is everything the aggregation adds. The signal state is predicted from a management system rather than asserted by the controller over a local radio, and it arrives after a backend round trip. For a time-to-green display and a speed suggestion that is acceptable. For a red-light violation warning, which is a safety function with a hard latency and integrity requirement, it is not. What signal services require · SPaT and MAP in the direct architecture
Why one automotive group built both.
| Volkswagen Car2X, Europe | Audi Traffic Light Information, United States | |
|---|---|---|
| Path | Direct 5.9 GHz radio | Cellular, through a backend |
| Infrastructure needed | Roadside units, where V2I is involved | None. Uses the existing traffic management system. |
| Ongoing cost to the driver | None. Volkswagen states the transmission is free of charge. | A connected-services subscription. |
| Latency class | Tens of milliseconds | Backend round trip |
| Safety-critical functions | In scope by design | Out of scope |
| Regulatory precondition | An allocated, stable band | None |
| What ended or limited it | Nothing. Still in production. | Backend lifecycle. See below. |
Neither choice was wrong for its market. Europe had an allocated band, a consortium and a road-operator programme, so the direct architecture was available and its benefits were reachable. The United States had none of those and, from 2019, active uncertainty about the band itself — so a manufacturer that wanted to ship a signal service in that market and that decade had exactly one option. What happened to the manufacturer that took the other option
A service bulletin, and the sharpest lesson in this section.
On 5 May 2023 Audi of America issued technical service bulletin 91 23 91, number 2070216/1, filed with the National Highway Traffic Safety Administration. It concerns 2017 model-year A4 and Q7 vehicles fitted with the virtual cockpit display, and its technical background section says this:
Due to technical updates to the Traffic Light Information Online backend systems, the online traffic light information function is not available on A4 and Q7 vehicles from model year 2017 built prior to a specified production week. These early vehicles were built with software that is no longer compatible with the backend server that provides the data to the vehicle. There is no software or hardware update solution that can resolve this concern.
The bulletin further records that the function is no longer supported for the affected vehicles, and that the connected-services licence was removed from their subscription package. It applies to that population and no wider: Audi states the service is still offered with an Audi connect PRIME subscription in most Audi vehicles on sale today.
Read carefully, that document describes a failure mode with no analogue in the direct-radio world:
- The vehicle did not fail. Its radio, its display and its software all work exactly as built.
- The service did not end for commercial reasons. It continues for newer cars.
- The car simply fell out of compatibility with a server it does not own. Six years after production, and roughly seven years after the function launched.
- There is no remedy. Not a software update, not a hardware replacement. The manufacturer says so in a document filed with a regulator.
A direct-radio system cannot fail this way, because there is no server. Its equivalent exposure is certificate expiry — a real and serious problem, and a solved one: certificates are renewable, the renewal mechanism is specified, and a vehicle whose credentials lapse can be re-provisioned. “No update can resolve this” is not a sentence that appears in that failure mode.
A cloud-mediated feature has a service life, and it is shorter than the car's.
Cars last fifteen to twenty years. Backend platforms are re-architected on a far shorter cycle, and the protocol a vehicle was built to speak in 2016 is not one anybody wants to keep serving in 2026. Somewhere between those two timescales, a feature that was sold as part of the vehicle stops existing.
Four requirements follow for anyone specifying a connected safety or traffic service:
- Write the service life into the specification. How long is the vehicle-to-backend interface contract supported, and what happens at the end of it? An unstated answer is still an answer; it is just discovered by the customer.
- Design the vehicle-side interface for versioning from the start. The failure recorded above is a compatibility failure between an old client and a new server, which is the most predictable problem in distributed systems and the one most reliably ignored when the client is welded into a dashboard.
- Prefer degradation to disappearance. A vehicle that loses the speed advisory but keeps time-to-green has lost a feature. A vehicle that loses the whole function and the licence with it has lost something it was sold.
- Weigh this against the direct architecture honestly. Direct radio costs spectrum, certification, silicon and an infrastructure programme. What it buys, among other things, is a function that keeps working because nothing has to keep running for it to work.
This is not an argument that cloud-mediated V2X is a mistake. It has delivered thousands of instrumented intersections in a market with no roadside radio estate, and no direct system achieved anything comparable there. It is an argument that the lifecycle cost is real, is now documented by a manufacturer in a regulatory filing, and belongs in the comparison rather than in a footnote. The full architecture comparison
Specifying a V2X on-board unit that has to stay serviceable for a vehicle lifetime? Interface versioning, credential renewal and field update are architecture decisions, not maintenance ones. Commissioning and service tools
Where this comes from.
- Audi of America — Technical Service Bulletin 91 23 91, number 2070216/1, 5 May 2023, filed with the National Highway Traffic Safety Administration. The affected 2017 model-year A4 and Q7 vehicles, the backend incompatibility, the absence of any software or hardware remedy, and the removal of the connected-services licence.
- Audi of America — Tech talk: Audi, Traffic Light Information and the future of what — and how — to drive. Audi’s own current statement: TLI offered with an Audi connect PRIME subscription in most Audi vehicles on sale today; the data partner collecting at more than 20,500 intersections across 96 agencies and cities in 26 US metropolitan areas. The article carries no publication date.
- Audi of America — Audi expands Traffic Light Information. The city list.
- Audi of America — Audi expands Traffic Light Information to include speed recommendations, February 2019. The green-light optimised speed advisory, described by Audi as a United States first.
- Virginia Office of the Secretary of Transportation — VDOT, Audi and TTS bring Traffic Light Information technology to Virginia. State transport agency confirmation of the partner and the deployment model.
External links are given so the figures can be checked at source. They do not imply any relationship with, or endorsement by, the organisations named. Audi, A4, Q7 and Audi connect are trademarks of AUDI AG, used here to identify the system studied.
Where this fits.
The global V2V audit
Every manufacturer investigated, classified by architecture, with the comparison matrix.
Volkswagen Car2X
The same automotive group, the direct architecture, and a function nobody can switch off.
Stellantis and HAAS Alert
The other large infrastructure-sourced deployment in the same market.
V2I
Signal phase, timing and geometry — what the direct architecture carries and why.
City mobility
What a city-scale programme delivers, and which party pays for each part of it.
United States regulation
The band history that made a cellular architecture the only shippable option.
Questions this page answers.
What is Audi Traffic Light Information?
A production vehicle-to-infrastructure service launched in the United States in 2016. Approaching an instrumented intersection, an equipped and subscribed vehicle displays the time remaining until the signal turns green. From February 2019 it also provides a green-light optimised speed advisory, a recommended speed calculated so that the driver arrives during a green interval rather than stopping.
Does Audi Traffic Light Information use DSRC or C-V2X?
Neither. There is no direct radio and no roadside unit. Signal phase and timing come from the municipal traffic management systems that already operate the intersections, pass through a signal-data aggregator and the manufacturer's backend, and reach the vehicle over its own 4G connection under a connected-services subscription.
Why did Audi use a cellular architecture instead of a roadside radio?
Because it required nothing of the road authority. A roadside-unit deployment means procuring, installing, powering, connecting, securing and maintaining a radio at every instrumented intersection. Taking the data from the traffic management system that already exists scaled to thousands of intersections in a market with almost no roadside V2X radio estate, and it avoided any dependence on a spectrum decision that was itself unsettled after 2019.
What happened to Traffic Light Information on early Audi models?
Audi of America issued technical service bulletin 91 23 91 on 5 May 2023, filed with the National Highway Traffic Safety Administration. It records that following technical updates to the backend, the function is not available on 2017 model-year A4 and Q7 vehicles built before a specified production week, that those vehicles carry software no longer compatible with the backend server, and that there is no software or hardware update solution. The connected-services licence was removed from the subscription package.
What does that bulletin teach about cloud-mediated V2X?
That a cloud-mediated feature has a service life shorter than the vehicle's. Cars last fifteen to twenty years; backend platforms are re-architected far more often. A direct-radio system cannot fail this way because there is no server. Its equivalent exposure is certificate expiry, which is a real problem but a solved one, since credentials are renewable and a vehicle whose credentials lapse can be re-provisioned.
Last updated 2026-09-08 · Technical reference maintained by Ambimat Electronics, Ahmedabad, India. Corrections: neel.shah@ambimat.com