Texting while crossing the road is the most distracting, and potentially most dangerous, activity, prompting the authors to suggest that a low tolerance approach similar to that taken towards drink-driving might be needed.

They base their findings on the behaviour of more than 1000 pedestrians crossing 20 busy road junctions in the north western city of Seattle during the summer of 2012 at different times of the day.

The observers recorded "distracting" activities, including talking on the phone, text messaging, or listening to music on mobile devices, as well as talking to others or dealing with children or pets.

Nearly half of the observations were made in the morning rush-hour between 8 and 9 am, and just over half of those observed were aged between 25 and 44.

Most (80%) were alone, and most (80%) obeyed the lights and crossed at the appropriate point (94%). However, only one in four pedestrians followed the full safety routine, including looking both ways before crossing.

And almost one in three (just under 30%) of the 1102 pedestrians were doing something else when they crossed the road. Around one in 10 (11%) were listening to music; 7% were texting; and 6% were talking on the phone.

Those who were distracted took significantly longer to cross the road -- 0.75 to1.29 seconds longer. While listening to music speeded up the time taken to cross the road, those doing it were less likely to look both ways before doing so.

People distracted by pets or children were almost three times as likely not to look both ways. But texting was potentially the most risky behaviour, the observations indicated.

Texters took almost two seconds (18%) longer to cross the average junction of three to four lanes than those who weren't texting at the time.

And they were also almost four times more likely to ignore lights, to cross at the middle of the junction, or fail to look both ways before stepping off the kerb.

The authors point out that crashes involving vehicles and pedestrians injure 60,000 people and kill 4000 every year in the USA, and just like distracted driving, distracted walking is potentially dangerous. It's also likely to increase as hand held mobile devices become ever more popular, they suggest.

"Individuals may feel they have 'safer use' than others, view commuting as 'down time,' or have compulsive behaviours around mobile device use," write the authors.

But the experimental evidence indicates that distractions impair awareness of surroundings, they say.

And they conclude: "Ultimately a shift in normative attitudes about pedestrian behaviour, similar to efforts around drunk-driving, will be important to limit the…risk of mobile device use."