Cellphone use in the United States has grown quickly during the past decade. There were more than 262 million wireless cellphone subscribers, representing 84 percent of the US population, as of June 2008, according to the Cellular Telecommunications and Internet Association.¹ That's up 35 percent from 194 million in June 2005 and nearly three times more than the 97 million wireless subscribers in June 2000. Minutes of use have surged to more than 1 trillion in June 2008 from 195 billion in June 2000.

Yes, though it's hard to accurately determine just how many drivers use phones. Observational data from the federal government indicate that 6 percent of drivers in 2007 were using hand-held phones at any moment during the day. The 2007 use rate means that about 1 million passenger vehicles on the road at any moment during the day are driven by people talking on hand-held phones.²

Females across all age groups are more frequently observed using hand-held cellphones than males (8 percent vs. 5 percent), according to daytime observational surveys of drivers conducted nationwide in 2007. Young drivers ages 16-24 also are much more likely than other drivers to talk on hand-held cellphones. Nine percent of drivers ages 16-24 were observed talking on hand-held phones, compared with 6 percent of those ages 25-69 and 1 percent of drivers 70 and older.²

Yes. Two controlled studies now link talking on a cellphone directly to increased crash risk. A 2005 Institute study of drivers in Western Australia found cellphone users four times as likely to get into crashes serious enough to injure themselves.³ The study used cellphone billing records to verify phone use of crash-involved drivers. Increased risk was similar for males and females, drivers younger than 30 and those 30 and older, and hands-free and hand-held phones. The findings were consistent with 1997 research that showed phone use among Canadian drivers was associated with a fourfold increase in the risk of a property damage crash. This study also used cellphone billing records.⁴

No, at least not after the conversation begins. Both studies of crashes using cellphone billing records to verify phone use found about a fourfold increase in crash risk with conversing on both hands-free and hand-held phones.^3,4 The studies were unable to estimate crash risk from different types of hands-free devices. They also were unable to determine whether there was any benefit associated with hands-free devices while placing the call. Experimental research using driving simulators indicates that phone conversation tasks, whether using hand-held or hands-free devices, affect some measures of driving performance.^5,6 Hands-free phones may eliminate some of the physical distraction of handling phones, but the cognitive distraction from phone conversations remains.

An Institute review of more than 120 cellphone studies, about half of which were experimental studies using driving simulators or instrumented vehicles, found that nearly all reported that some measures of driver performance were affected by the cognitive distractions associated with cellphone tasks.⁶ Phone conversation tasks typically decreased reaction times and travel speeds and increased lane deviations and steering wheel movements. A statistical analysis that aggregated the results of 33 studies reported similar findings.⁵ Some studies also have found that older drivers' performance is more affected by cellphone tasks, particularly their reaction time. Few studies included drivers younger than 18, and evidence is mixed on the effects of phone use for teenage drivers compared with adult drivers. Findings also are mixed on whether driving performance while talking on a cellphone improves with practice. Some simulator studies suggest that the negative impact of phone use on driving performance may lessen with experience.^7,8 Other simulator research has found no change in performance with practice.⁹

Further evidence comes from a few studies of small samples of people observed during their everyday driving. One study included drivers of 100 vehicles instrumented with video cameras and other monitoring technologies. Only a few serious crashes occurred, but researchers calculated the odds of being in a near-crash or crash were higher when dialing a hand-held phone than when phones weren't being used.¹⁰

Not in the US, but bans are widespread in other countries. Six US states (California, Connecticut, New Jersey, New York, Utah, Washington) and the District of Columbia have enacted laws that ban drivers of all ages from using hand-held cellphones. More common in the US are laws that restrict young drivers from using any type of cellphone or messaging device. Teenage drivers in 17 states and Washington, DC, are barred from talking on any type of cellphone. In addition, Louisiana has passed a law restricting teen use of cell phones, but as of September 2008, it is not clear whether it bans all cell phone use or use of hand-held cell phones. School bus drivers in 16 states and Washington, DC, are restricted from using all cellphones while driving a bus. As of June 2008, a number of jurisdictions world-wide including Australia, Japan, most European countries and several Canadian provinces ban hand-held phones while driving.

Text messaging is banned for all drivers in 7 states (Alaska, California, Connecticut, Louisiana, Minnesota, New Jersey, and Washington) and the District of Columbia. In addition, novice drivers are banned from texting in 9 states (Delaware, Maine, Maryland, Nebraska, North Carolina, Oregon, Texas, Virginia, and West Virginia) and school bus drivers are banned from text messaging in 4 states (Arkansas, North Carolina, Texas, and Virginia).

Cellphone laws in the US

Their effect on real-world crashes hasn't been determined, but Institute studies have documented how bans enacted in the US have affected drivers' hand-held cellphone use. New York was the first state to implement a ban on hand-held cellphones for drivers. Driver hand-held cellphone use dropped by half immediately following implementation of the 2001 law, but this decline had substantially dissipated one year later.¹¹ In contrast, soon after Washington, DC, began banning hand-held phone use while driving in 2004, driver hand-held cellphone use dropped by about half, and this decline was sustained about a year later. It's likely that stronger enforcement of the DC ban led to the sustained lower use rates compared with New York. Citations for cellphone violations represented 8 percent of all moving violations in DC compared with 4 percent in New York.¹²

Given that crash risk increases substantially with drivers' use of either hand-held or hands-free phones, bans on hand-held cellphones will not eliminate the problem entirely. The problem with laws prohibiting hands-free phones is that they are difficult to enforce.

Cellphone bans for young drivers are becoming commonplace amid concerns about the role distractions play in teenagers' elevated crash risk. Distractions of any type are a common factor in crashes of newly licensed 16-year-old drivers.¹³ Some research also shows teenage drivers tend to use cellphones and other emerging technologies more than adult drivers.¹⁴ States increasingly have graduated licensing laws that place restrictions on newly licensed drivers, e.g., limiting nighttime driving and the number of passengers a novice driver can carry. Cellphone bans are being added to those restrictions.

See Q&A: Teenagers — graduated driver licensing

More about the licensing law in your state, or any state

Young drivers often ignore cellphone restrictions, a 2008 Institute study of North Carolina's cellphone ban for young beginning drivers found. The state bans the use of any telecommunications device by drivers younger than 18 under its graduated licensing system. Observed cellphone use by teenagers leaving high schools in the afternoon changed little from 1-2 months before and 5 months after the restriction took effect on Dec. 1, 2006. About 11 percent of teen drivers were seen using phones before the law. That percentage rose slightly to 12 percent in the postlaw survey. Cellphone use remained steady at about 13 percent at comparison sites in South Carolina, which doesn't restrict teen drivers' phone use. When observed postlaw, less than 1 percent of teenage drivers in North Carolina were using hands-free phones. About 2 percent were observed dialing or texting and about 9 percent were holding a phone to their ear.

The study coupled driver observations with telephone surveys of North Carolina parents and their teens. In postlaw surveys, about two-thirds of teens said they knew about their state's law, compared with 39 percent of parents. Three-quarters of teens and 95 percent of parents said they approved of the law. The proportion of teenagers who reported using phones while driving declined somewhat following the law. However, of those who owned a phone and admitted to ever talking on the phone while driving, about half admitted they used their phones, if they had driven, on the day prior to the interview. There was no evidence of focused enforcement or publicity of the law. Only 22 percent of teenagers and 13 percent of parents believed the ban was being enforced fairly often or a lot.¹⁵

Evidence is mixed. For example, some experimental studies found that phone conversations are more disruptive than conversations with passengers or adjusting a radio.⁶ However, a statistical analysis combining the results of several experimental studies found similar decrements in reaction time for conversation tasks with passengers and with hand-held or hands-free phones.⁵ Two studies suggest that talking on cellphones or having a 0.08 percent blood alcohol concentration (BAC) — the legal threshold for impairment — has a comparable effect on some simulated driving tasks.^16,17 However, the risks associated with alcohol impairment accumulate over the entire duration of a trip, whereas the risks of cellphone use generally apply for only a portion of a trip. In addition, crash risk increases substantially at very high BACs, and the implications of the experimental studies for drivers in their own vehicles is unknown.