Enacting a cellphone ban has been linked with a relative decrease in the accident rate in urban areas.
However, in very rural areas, cellphone bans were associated with higher accident rates than would otherwise be expected.
"The main idea is to use the eye test when it comes to cellphone use," says study leader Sheldon H. Jacobson, a professor of computer science and mathematics at the University of Illinois.
"If you look around and it's busy, it's a good idea to put the cellphone down and not use it when driving."
The Illinois study is set apart by two factors: the length of time and the method of measuring driver density.
The study examines long-term trends of accident rates and their association with cellphone bans, comparing seven years of driver data in New York - the first state to institute a statewide ban - and neighboring Pennsylvania, which has no ban. Both states have similar weather patterns and wide diversity in size and population density of counties.
"What we found in our research is that the cellphone ban was associated with different outcomes in different groups of counties," said industrial and enterprise systems engineering researcher Douglas King, a co-author of the study.
"Based on this research, it suggests that a blanket cellphone ban may not always lead to a greater benefit. Based on the seven-year time period that we were able to examine, the outcome in each group of counties after the ban was not uniformly beneficial."
The study has been published in the journal Transportation Research Part A: Policy and Practice.