Vehicle-to-infrastructure (V2I) is now operational in the US, with cars connecting to traffic lights to tell their drivers how many seconds away the green light is.

Available on select Audi cars driving only in Las Vegas for now, the system uses the car's on-board 4G internet connection to receive traffic light data from the area's traffic management system.

In a bid to reduce driver stress, the system displays the number of seconds the red light has left in the car's digital instrument cluster, between the rev counter and speedometer, and on the head-up display if fitted. Audi says drivers are more relaxed when they know how long they have until the green light appears. But the system will also lead to advances in self-driving car technology.

Scott Keogh, president of Audi of America, said: "V2I applications and services like traffic light information are essential components as we continue to move toward an autonomous future. We applaud the innovative approach of Las Vegas in working with us on V2I as well as on our various piloted driving demonstrations over the past years."

The feature, only available in Las Vegas for now, is exclusive to models of the Audi A4, Q7 and A4 Allroad manufactured after 1 June 2016 and equipped with an active Audi Connect Prime subscription.

A countdown to the green light is just the first feature of several Audi has planned using the same vehicle to infrastructure technology. The company says: "In the future, it may be possible to integrate information from these advanced traffic management systems into vehicle start/stop features and navigation systems to optimise routing."

One of the most interesting features proposed by Audi is one where the car will suggest the ideal speed to "maximise the number of green lights one can make in sequence."

Tina Quigley, general manager of the Southern Nevada Regional Transportation Commission, said: "This V2I technology will help reduce congestion and enhance mobility on our already crowded roadways."

The news comes just weeks after Ford announced it is testing and developing a similar system in the UK. Here, roadside units broadcast traffic light information to approaching cars, which then suggest a recommend speed at which the most consecutive green lights will be passed. Ford explains: "Green Light Optimal Speed Advisory uses information on traffic light timings from a roadside unit to display to the driver the best speed to travel at to get a green light."