The Multi-Tasking Driver: Risks to Public Safety David Strayer Department of Psychology Center for the Prevention of Distracted Driving May 5,2010

An Epidemic of Driver Distraction

Research Questions  Does conversing on a cell phone interfere with driving?  What are the sources of the interference?  Peripheral interference (dialing, holding the phone)  Cognitive interference (cell phone conversation)  How significant is the interference?

On-road Study of Over 1700 Drivers  Observed drivers as they approached a 4-way intersection with stop signs in all directions  6 hours, 2 hours at each of 3 intersections  5:00 – 6:00 PM  Mondays, Wednesdays, Fridays  Good driving conditions  Was the driver using their cell phone?  Did the driver stop at the white stop line?

Observational Study (Residential 4-way Intersections)  Odds ratio for failing to stop:  0.27 for drivers not using a cell phone  2.93 for drivers using a cell phone Traffic Violation No Traffic Violation On Cell Not on Cell  2(1)=129.8, p<.01

Epidemiological Evidence  New England Journal of Medicine (1997)  699 driver involved in a non-injury automobile accident  4-fold increase in risk of accident when using cell phone  British Medical Journal (2005)  456 drivers requiring hospital attendance after automobile accident  4-fold increased likelihood of crashing when using a cell phone

Single-Task vs. Dual-Task 20% 15% 4-fold increase in accidents

Summary  Cell-phone driver’s  Slower reaction times  Drivers compensate by increasing following distance  Increase in rear-end accidents (by a factor of 4)  Cell-phone interference  Even when manual contributions are eliminated  Clear evidence of cognitive distraction

Why Do Cell Phones Cause Interference?  From earlier studies, no interference from:  Radio broadcasts (audio input)  Books on tape & recorded conversations (audio/verbal input)  Simple shadowing (audio/verbal input, verbal output)  Implies active engagement in conversation necessary  Impairments from both hand-held and hands-free units  Implies central / cognitive locus  Inattention-blindness (James, Neisser, Simons)

Basketball Counting Test

Inattention-Blindness  Test for evidence of cell-phone induced inattention blindness  High-fidelity driving simulator  Hands-free cell phone  Naturalistic conversation with confederate  Eye tracker  Two phases to the study:  Phase 1: Single & dual-task driving  Phase 2: Recognition memory tests for objects encountered while driving

Recognition Memory Given Fixation

Summary  50% drop in recognition memory from single to dual-task, consistent with inattention blindness interpretation  What about items more relevant to safe driving?  Drivers DO NOT divert attention from processing items of low task relevance (e.g., billboards), and protect high task relevance items (e.g., pedestrians)?

Encoding or Retrieval Deficits?  Encoding deficits  Reduced attention to perceptual inputs  Clear implications for traffic safety  Retrieval deficits  Failure to retrieve prior episodes  Less clear implications for traffic safety  Event-related brain potentials recorded to traffic brake lights  Single-task  Dual-task

Traffic-Related Brain Activity

Cell Phone vs. Passenger Conversations  Conditions  Single task / dual task  Conversing on cell phone  Conversing with passenger  Design  Task (2) x Condition (2) Single task Cell Passenger

Lane Keeping Errors

Successful Navigation

How Significant is the Interference?  Cell-phone vs. drunk-driver  Redelmeier and Tibshirani (1997) reported epidemiological evidence suggesting that “the relative risk [of being in a traffic accident while using a cell-phone] is similar to the hazard associated with driving with a blood alcohol level at the legal limit” (p. 465).

Summary  Compared to drunk driver, cell-phone driver’s reactions  Slower reaction times  Longer to recover lost speed following braking  Drivers compensate by increasing following distance  Increase in rear-end accidents  When controlling for time on task and driving conditions, cell-phone drivers’ performance is worse than that of the drunk driver

Text Messaging & Driving  90% of public support laws banning texting while driving  50% of teens report texting while driving  What are the risks?

Text Messaging and Driving  Accident odds ratio of 8.1 Traffic Accident No Accident Single-Task Dual-Task

Cognitive Interference: Tunnel Vision

Cognitive Interference: Inattention Blindness

Research Questions  Does conversing on a cell phone interfere with driving?  Yes  What are the sources of the interference?  Peripheral interference (dialing)  Cognitive interference (inattention blindness)  How significant is the interference?  Worse than listening to radio/books on tape  Worse than in-vehicle conversations  More impairing than driving while legally intoxicated