The number of accidents involving pedestrians wearing headphones is on the rise, a report suggests, prompting fresh warnings from road safety groups in Britain.
A US-based study, which appeared in the BMJ journal Injury Prevention, found a total of 116 reports of death or injury to pedestrians wearing headphones between 2004 and 2011, jumping from 16 in 2004/5 to 47 in 20110/11.
Most victims were men (68%) and under the age of 30 (67%), with around one in 10 of all cases (9%) under the age of 18.
Some 89% of the cases occurred in urban areas and more than half (55%) of the victims were struck by trains.
Eighty-one of the 116 collisions (70%) resulted in the person dying - even though a warning such as a siren was sounded in around a third of the cases.
The study concluded: "The use of headphones with handheld devices may pose a safety risk to pedestrians, especially in environments with moving vehicles. Further research is needed to determine if and how headphone use compromises pedestrian safety."
British road safety groups warned pedestrians to take caution.
Floor Lieshout, director of Youth For Road Safety, told the Huffington Post UK: "This study shows once more the importance of using all of our senses while we participate in traffic. It is a very disturbing trend and it is vital we find an appealing way to make youth, especially young males, aware of the risks wearing headphones in traffic."
Others warned that more research needed to be done before conclusive findings could be drawn.
Andrew Howard, who is the head of road safety at the AA, added that some pedestrians can be "so wrapped up in their own little bubble they forget the world going on around them".
That can include headphone wearers, Howard said, but also people talking on phones and even people walking with hoods up.
"It's almost a bubble-effect," he said.
However, Howard said that more research needed to be done.
"All we can do is say that is very hard to prove what the stats are in Britain," he said. "The difficulty is getting any kinds of figure. For instance it's relatively easy to track a driver when he is using a phone but not when he's using an iPod, never mind cyclists and pedestrians."
Previous studies have shown that people wearing headphones or talking on phones can suffer "inattentional blindness" which makes them effectively isolated from the world around them.
Ian Harvey, at the charity Civic Voice, said that "to overcome isolation and to help build a civic society, people need to interact with each other".
He said: "A basis for any civilised society is communication... Surfing the web, listening to MP3s, reading blogs or sending email is not interacting with a person; it's interacting with a machine.
"If people feel socially isolated, they need to have more face-to-face interactions with other human beings and in time, will begin to feel happier and more connected to the world and place they live in."
Cycling safety groups added that a line needed to be drawn between sound isolation and environmental isolation, especially since, for instance, deaf people are not disqualified from cycling and policies needed to reflect that.
Chris Peck, policy coordinator at cycling safety group CTC, said:
"Although a lot of cyclist do use their hearing to alert them to hazards on the roads, there is no rule against the deaf cycling. It's probably not the kind of thing a sensible cyclist would do, but we don't think there should be a law against it.
"If pedestrians are unaware of their surroundings then communication is going to be harder, but the same thing would apply to people in cars playing very loud music."
A spokesperson for the Mayor of London Boris Johnson said that while the number of pedestrians killed in London had "halved" in the last 10 years, TFL would address the issue in its future road safety plans.
"As part of the continued push to cut accidents on London's road network, the mayor is finalising his road safety plan for the next decade," the spokesperson said.
"This is an issue the mayor has himself raised with TFL and he has asked that it be investigated actively as part of that work."