Led by Rutgers University researchers in Newark, New Jersey, the studies have shown that whether travellers use the phone while driving or while walking, it is increasing the deaths of pedestrians as well as those of drivers and passengers.

Economics Professor Peter D Loeb, lead author of the studies, has recommended crackdowns on cell use by both pedestrians and drivers.

He says that the new studies relate the impact of cell phones on accident fatalities to the number of cell phones in use, showing that the current increase in deaths attributed to cell phone use follows a period when cell phones actually helped to reduce pedestrian and traffic fatalities.

The researcher said that that reduction in fatalities disappeared after the numbers of phones in use reached a “critical mass” of 100 million.

While conducting the studies, the researchers focused on cell phone use and motor vehicle accidents from 1975 through 2002, and factored in a number of variables, including vehicle speed, alcohol consumption, seat belt use, and miles driven.

They found the cell phone-fatality correlation to be true even when weighing in factors like speed, alcohol consumption, and seat belt use.

Loeb says that, at the current time, cell phone use has a “significant adverse effect on pedestrian safety” and that “cell phones and their usage above a critical threshold adds to motor vehicle fatalities.”

According to him, in the late 1980s and part of the 1990s, before the numbers of phones exploded, cell phone use actually had a “life-saving effect” in pedestrian and traffic accidents.

“Cell-phone users’ were able to quickly call for medical assistance when involved in an accident. This quick medical response actually reduced the number of traffic deaths for a time,” Loeb hypothesizes.

However, that was not the case when cells were first used in the mid-1980s, when they caused a “life-taking effect” among pedestrians, drivers and passengers in vehicles.

Loeb said that in the early days, when there were fewer than a million phones, fatalities increased because drivers and pedestrians probably were still adjusting to the novelty of using them, and there weren’t enough cell phones in use to make a difference in summoning help following an accident.

He added that the “life-saving effect” occurred as the volume of phones grew into the early 1990s, and increasing numbers of cells were used to call 911 following accidents, leading to a drop in fatalities.

However, he said, the life-saving effect was cancelled out when the numbers of phones nearly touched the 100 million mark, and increased accidents and fatalities outweighed the benefits of quick access to 911 services.