Q&A: Older drivers

December 2010

1 How many older drivers are there?

In 2009, there were an estimated 27.8 million people 70 and older living in the United States, representing about 9 percent of the population.1 Based on data reported by states to the Federal Highway Administration, there were approximately 21.6 million licensed drivers 70 and older in 2008. This represented approximately 78 percent of the population 70 and older and about 10 percent of drivers of all ages.

2 How are the numbers of older drivers and their crash rates changing over time?

Compared with drivers ages 20-69, fewer people 70 and older are licensed to drive, and they drive fewer miles per licensed driver. However, older people now keep their licenses longer, drive more miles, and make up a bigger proportion of the population than in past years as baby boomers age. Based on data from the Federal Highway Administration, there were nearly 22 million licensed drivers 70 and older in 2008, compared with just under 18 million in 1997. These drivers represented 78 percent of the older driver population in 2008, compared with 73 percent in 1997.

The rapid increase in the older driver population has led to concerns about the potential effects on traffic safety associated with this trend. A 2003 study examined historical crash rates of older drivers and projected that older drivers would become an increasing proportion of the overall crash problem, including fatal crashes.2 However, despite growing numbers on the road, fewer older drivers died in crashes and fewer were involved in fatal collisions during 1997-2009 than in years past. A total of 3,981 people ages 70 and older died in motor vehicle crashes in 2009. This is 32 percent fewer than in 1997, reversing an upward trend and occurring even as the population of people 70 and older rose 13 percent. The rate of fatalities per capita among older people has decreased 45 percent since 1975 and is now at its lowest level.

A 2009 Institute study examined recent trends in crash involvements per licensed driver among drivers 70 and older. Nationally, the fatal crash involvement rate for drivers 70 and older declined from 1997 to 2008, and did so at a faster pace than the rate for drivers 35-54 years old. The reductions were strongest among the oldest drivers (age 80 and older). If the fatal crash involvement rates for older drivers had mirrored the trend for middle-age drivers from 1997 to 2008, about 10,000 additional older drivers would have been in fatal crashes. Based on data on police-reported crashes from 13 states, nonfatal injury crash involvement rates showed similarly larger-than-expected declines for older drivers during 1997-2005, but the reductions in crash rates were not significantly larger than for 35-54 year-olds. Involvement rates in crashes with only property damage declined for older drivers but increased for middle-age drivers. The analyses also showed that the odds of an older person surviving a crash have increased while the odds of a middle-age person surviving have stayed about the same. Thus, the reduced fatality risk of older drivers reflects both a lower likelihood of being involved in a police-reported crash and a greater likelihood that they will survive when they do crash.3

Number of fatal crashes among drivers 70 and older per 100,000 people 70 and older

3 How much do seniors drive?

Based on 2001-02 data, drivers 70 and older drove 55 percent fewer annual miles, on average, than drivers ages 35-69.4 An Institute study of drivers 65 and older found that drivers with reported impairments in memory, vision, mobility, and/or medical conditions such as arthritis or diabetes were more likely than other drivers to self-limit their driving by making fewer trips, traveling shorter distances, and avoiding night driving, driving on interstates, and driving in ice or snow.5 This supports other research showing that many older drivers self-limit their driving.6,7,8,9,10,11,12,13,14 However, some seniors do not self-regulate or adjust their driving,6,7 even those with high levels of cognitive impairment.13

4 How do crash rates for older drivers compare with those for drivers of other ages?

Older drivers have low rates of police-reported crash involvements per capita, but per mile traveled crash rates start increasing for drivers 70 and older and increase markedly after age 80. Some caution should be used when examining crash rates per mile traveled, especially for older drivers. Older drivers generally travel fewer annual miles than most other age groups and, similar to low-mileage drivers of other ages, they tend to accumulate much of their mileage in city driving conditions. In contrast, drivers who accumulate higher annual miles tend to do so on freeways or divided multilane roads, which generally have much lower crash rates per mile traveled than other types of roads. Hence, the elevated crash rates for older drivers when measured per mile traveled may be somewhat inflated due to the type of driving they do.15

Number of crashes per capita by driver age, 2009

 

Number of crashes per mile traveled by driver age, 2001-02

Insurance claims provide a more comprehensive picture of crashes of all severities than police crash reports because police are not notified of many crashes reported to insurers, and police-reported crashes are more likely to involve injury. Property damage liability claims are filed when an at-fault driver damages someone else's property. Collision coverage insures one's own vehicle against loss caused by a collision. Although not as high as for the youngest drivers, property damage liability claims and collision claims per insured vehicle year (for 2002-04 models) start increasing after about age 65, meaning that seniors are involved in crashes more often.16

Number of collision and property damage liability claims per 100 insured vehicle years by rated driver age, 2004-08 models, calendar years 2007-08

5 To what extent does fragility contribute to older drivers' fatal crash rates?

A study of older drivers' elevated fatal crash rates per mile traveled between 1993 and 1997 revealed that the main factor was not seniors' overinvolvement in crashes but their fragility, defined as the risk of death in a crash.17 Fragility increased starting around ages 60-64 and continued to rise with age. Similar results are found with more recent data for 2005-09.

Number of passenger vehicle driver deaths per 1,000 drivers involved in police-reported crashes by driver age, 2005-09

6 How do crashes involving older drivers differ from the crashes of other drivers?

Compared with younger drivers, senior drivers are more likely to be involved in certain types of collisions — angle crashes, overtaking or merging crashes, and especially intersection crashes. The most common error made in senior-involved crashes is failure to yield the right-of-way. Seniors are cited for this error more often than younger drivers.18 In a 2007 Institute study of nonfatal crashes at intersections, drivers 80 and older had fewer rear-end crashes than drivers ages 35-54 and 70-79, and both groups of older drivers had more failure-to-yield crashes and fewer ran-off-road crashes than younger drivers. Reasons for older drivers' failure-to-yield crashes varied with age. Compared with younger and older drivers, drivers 70-79 were more likely to see another vehicle but misjudge whether there was time to proceed. Drivers 80 and older predominantly failed to see the other vehicle.19

7 Do age-related changes affect driving ability?

Specific physical, cognitive, and visual abilities may decline with advancing age. However, there are large individual differences in the onset and degree of functional impairments, so age alone is not sufficient information to judge driving ability. Still, functional impairments can interfere with driving and may become particularly evident in stressful or challenging driving situations such as merging or changing lanes. Several studies have shown that higher levels of physical, cognitive, or visual impairment among older drivers are associated with increased risk of crash involvement.12,20,21,22 Many older drivers also take medications, which can impair driving ability at any age but can be especially impairing for an older person.

8 Do older drivers constitute a substantial hazard to other road users?

In terms of fatalities, older drivers are a danger mostly to themselves and their passengers, who also typically are older and thus more vulnerable to injuries.23,24,25,26 In 2009, 74 percent of people killed in crashes involving a driver 70 or older were either the older driver themselves (61 percent), or their older passengers (13 percent). One study found that per licensed driver, drivers 75 and older kill fewer pedestrians, bicyclists, motorcyclists, and occupants in other vehicles compared with drivers ages 30-59. In the fatal crashes of drivers 75 and older, the drivers and their senior passengers were much more likely to be killed than were occupants in other vehicles. 23 However, drivers 70 and older have higher insurance liability claims for damage to other vehicles per insured vehicle year than drivers ages 35-69.16

9 Can screening tests identify drivers who are at greater crash risk than other drivers?

The goal of driver screening is to identify people at high risk of crash involvement without falsely identifying other drivers who are not at high risk. So far, there are no tests that accomplish this goal with sufficient accuracy.

A few states including California and Maryland are studying tiered screening tests. California developed and pilot-tested a three-tier assessment for driver's license renewal for applicants of all ages.27 The first two tiers consist of nondriving assessment tools (e.g., driving knowledge test, cognitive screening, vision tests, observation of obvious physical limitations). Applicants failing both tiers must pass an on-road driving test to renew their licenses. A pilot study found that lower assessment scores in the first two tiers were related to worse performance on the road test but were not consistently related to crash records during the three years prior to renewal.27 A pilot study in Maryland found that drivers who performed poorly on select cognitive measures were approximately 25 percent more likely than other drivers to have a subsequent at-fault crash after controlling for age, gender, and annual mileage.28

Although these findings suggest a general relationship between some measures of cognitive ability and crash risk, it is not clear whether these tests are sufficiently sensitive to predict future crash risk with the accuracy that would be required to justify suspending license privileges.

10 Are state rules for driver's license renewal different for older drivers?

A growing number of states have imposed additional requirements for seniors renewing their driver's licenses. The ages at which special regulations are required vary by state but typically begin at ages 65-75. More than half the states have one or more renewal provisions specific to older drivers such as shorter renewal cycles, required vision or road testing, and in-person rather than mail or electronic renewal. For details, see US driver licensing renewal procedures for older drivers.

US driver licensing renewal procedures for older drivers

An Institute study of a Florida vision test requirement for drivers 80 and older found that 80 percent of those eligible to renew their licenses attempted to do so, and only 7 percent of drivers were denied renewal because they failed the vision test. Of those who did not seek renewal, about half said they thought they would fail the vision test.29

11 Do special regulations for driver's license renewal among older drivers affect crash rates?

Studies have yielded mixed results. Several studies have shown that vision testing among seniors was associated with lower fatal crash rates per population30,31 and per licensed driver.32 In one study, states with laws requiring in-person driver's license renewal had a 17 percent lower fatality rate per licensed driver among the oldest drivers (i.e., 85 and older), compared with states without such laws. For drivers 65 and older, fatality rates per licensed driver did not differ for states with and without laws for vision testing, road testing, or shortened renewal periods.33 Similarly, an Australian study found that drivers 80 and older in jurisdictions with age-based mandatory medical and/or road tests did not have lower fatal and serious injury crash involvement rates per capita or per licensed driver compared with a jurisdiction without age-based mandatory testing. Some jurisdictions with mandatory age-based testing had significantly higher fatal and serious injury crash rates than the jurisdiction without age-based testing.34 Thus the effects of special regulations for license renewal among older drivers are not well established.

12 Do states place driving restrictions on older drivers? If so, what are the effects?

States may impose license restrictions on a driver of any age, but restrictions are imposed mostly on teenagers and older drivers. The goal of restricted licensing is to allow drivers to continue to drive in conditions that are safe for them, based on individual abilities. Possible restrictions include no driving on high-speed roads, outside a certain area, or at night.

No state restricts older drivers based on age alone. The restrictions generally are based on evaluations that may be conducted when drivers apply for license renewal. Drivers may be subject to evaluations by licensing agencies based on referrals from police, physicians, or family. States may establish policies for further testing that include vision screening, road tests, knowledge tests, and/or evaluations by medical advisory boards.

An Institute study of a restricted licensing program in Iowa found that drivers 70 and older who were identified for further testing reported more visual impairments, prescription medications, and physical mobility limitations. Driving exposure was reduced more among older drivers who received restrictions than among drivers who did not receive restrictions. It appeared that restrictions reinforced decisions some older drivers already had made to decrease or self-regulate their trips by driving less or reducing or eliminating driving in risky situations such as nighttime outings. The effects of restrictions on crashes are unknown.35

13 Do older drivers self-limit the amount of driving that they do?

An Institute survey of more than 2,500 drivers ages 65 and older in 3 states found that drivers travel fewer miles with increasing age.5 Drivers 80 and older were more than twice as likely as 65-69 year-olds to self-limit their driving by doing such things as avoiding night driving, making fewer trips, traveling shorter distances, and avoiding interstate highways and roads that are icy or snowy. Drivers of any age reporting impairments in physical mobility, vision, or memory, or those with more reported medical conditions, were more likely to restrict their driving. These survey findings mirror earlier reports.7,8,9,13,36,37

The Institute study of a restricted licensing program in Iowa found that many drivers 70 and older who received restrictions on their license — prohibiting driving when headlights are required, on interstates or high-speed roads, or outside of a geographic area — were already limiting their driving in those situations to some degree.35

14 Is driver education beneficial for older drivers?

There is little evidence of safety benefits from education courses for older drivers, although several organizations offer such courses. National programs include the Driver Safety Program (American Association of Retired Persons), Safe Driving for Mature Operators (American Automobile Association), and Coaching the Mature Driver (National Safety Council).

A challenge in evaluating these courses is to design studies that separate the effects of the course from the effects due to differences in the types of drivers who participate. Drivers who choose to take these courses typically have lower crash rates prior to the course than those who do not participate. None of the evaluations of older driver improvement programs or educational initiatives have found a reduction in subsequent crash risk among participants relative to comparison groups.38,39,40,41,42

15 How can new vehicle features improve safety for older drivers?

Technologies to enhance occupant protection in crashes include safety belt force limiters that limit the force of restraints during a crash and advanced airbags that reduce the likelihood of injuries resulting from airbags. Improved head restraint systems help protect occupants against whiplash and other neck injuries. Some vehicles also provide ergonomic features that may assist older drivers, including adjustable pedals and seat adjusters, as well as bigger and brighter displays and controls.

Vehicle technologies intended to prevent crashes may help drivers of all ages. Electronic stability control, a technology intended to increase a vehicle's stability, has been found to be highly effective in reducing single-vehicle fatal crash involvement risk.43 Other crash avoidance systems include lane departure warning, forward collision warning, and side view assist, also known as blind spot detection. Despite the potential benefits of these technologies for helping to prevent crashes, there is some concern that systems requiring attention or responses from drivers may lead to cognitive overload or distraction from the driving task itself, especially for older drivers.

16 What changes in the driving environment could improve safety for older drivers?

Much can be done to improve roadway safety for all drivers, but especially for seniors. Improving the visibility of road signs and pavement markings through lettering, size, or color can be particularly important for older drivers who may have visual impairments due to macular degeneration, glaucoma, cataracts, or other health factors. Intersections are a particular problem for older drivers, and countermeasures may include adding left-turn lanes and left-turn traffic signals. One study found that low-cost modifications to intersections (e.g., making traffic signals more visible, adding a dedicated left-turn lane) resulted in a 13 percent greater reduction in injury crashes per licensed driver for drivers 65 and older compared with drivers ages 25-64.44

Another approach is to reconfigure existing or new intersections as roundabouts, which reduce vehicle speeds and eliminate some of the most complicated aspects of traditional intersections. In a study of intersections that were converted from stop signs or traffic signals to roundabouts, injury crashes were reduced by 76 percent.45 However, older drivers favor roundabouts somewhat less than younger drivers. In surveys taken at least one year after the construction of new roundabouts in six communities, 65 percent of drivers ages 65 and older favored the roundabouts, compared with 70 percent of drivers 35-64, and 74 percent of drivers 18-34.46 No studies have focused on the effects of roundabouts on crashes among older drivers who may find them difficult to navigate. Adding features to roundabouts such as advanced warning signs and directional signs may encourage older drivers to choose routes with roundabouts as opposed to conventional intersections.47

17 Are alternatives to driving available for older people?

Better and more widely available alternatives to driving for older people, particularly in rural communities, are needed. Walking may not be feasible in some communities, and friends and family may be needed to provide rides. Other alternatives, although not available in many areas, include public transportation and community-based systems such as van programs and volunteer drivers. In a national telephone survey, public transportation was the usual mode of transportation for 5 percent of all adults 75 and older and for 14 percent of adults 75 and older who did not drive.48

References

¹US Census Bureau. 2009. Population estimates. Washington, DC.

²Lyman, S.; Ferguson, S.A.; and Williams, A.F. 2002. Older driver involvements in police reported crashes and fatal crashes: trends and projections. Injury Prevention 8:116-20.

³Cheung, I. and McCartt, A.T. 2010. Declines in fatal crashes of older drivers: Changes in crash risk and survivability. Arlington, VA: Insurance Institute for Highway Safety.

⁴Federal Highway Administration. 2001. National Household Travel Survey, 2001. Washington, DC.

⁵Braitman, K.A. and McCartt, A.T. 2008. Characteristics of older drivers who self-limit their driving. Proceedings of the 52^nd Annual Conference of the Association for the Advancement of Automotive Medicine. Barrington, IL: Association for the Advancement of Automotive Medicine.

⁶Baldock, M.; Mathias, J.; McLean, A.; and Berndt, A. 2004. Self-regulation of driving and its relationship to driving ability among older adults. Proceedings of the 2004 Road Safety, Research, Policing, and Education Conference (CD-ROM). Perth, Western Australia: Impact Communications Pty Ltd.

⁷Ball, K.; Owsley, C.; Stalvey, B.; Roenker, D.L.; Sloane, M.E.; and Graves, M. 1998. Driving avoidance and functional impairment in older drivers. Accident Analysis and Prevention 30:313-22.

⁸Charlton, J.L.; Oxley, J.; Fildes, B.; Oxley, P.; and Newstead, S. 2003. Self-regulator behaviors of older drivers. Proceedings of the 47th Annual Conference of the Association for the Advancement of Automotive Medicine. Barrington, IL: Association for the Advancement of Automotive Medicine.

⁹Lyman, J.M.; McGwin, G., Jr.; and Sims, R.V. 2001. Factors relating to driving difficulty and habits in older drivers. Accident Analysis and Prevention 33:413-21.

¹⁰Marottoli, R.A.; Ostfeld, A.M.; Merrill, S.S.; Perlman, G.D.; Filey, D.J.; and Cooney, L.M., Jr. 1993. Driving cessation and changes in mileage driven among elderly individuals. Journal of Gerontology 48:S255-S260.

¹¹West, C.G.; Gildengorin, G.; Haegerstrom-Portnoy, G.; Lott, L.A.; Schneck, M.E.; and Brabyn, J.A. 2003. Vision and driving self-restriction in older adults. Journal of the American Geriatrics Society 51:1348-55.

¹²Owsley, C.; Ball, K.; Sloane, M.E.; Roenker, D.L.; and Bruni, J.R. 1991. Visual/cognitive correlates of vehicle accidents in older drivers. Psychology and Aging 6:403-15.

¹³Stutts, J. 1998. Do older drivers with visual and cognitive impairments drive less? Journal of the American Geriatrics Society 46:854-61.

¹⁴Keay, L; Munoz, B.; Turano, K.A.; Hassan, S.E.; Munro, C.A.; Duncan, D.D.; Baldwin, K.; Jasti, S.; Gower, E.W.; and West, S.K. 2009. Visual and cognitive deficits predict stopping or restricting driving: The Salisbury Eye Evaluation Driving Study (SEEDS). Investigative Ophthalmology and Visual Science 50:107-113.

¹⁵Janke, M.K. 1991. Accidents, mileage, and the exaggeration of risk. Accident Analysis and Prevention 23:183-88.

¹⁶Highway Loss Data Institute. 2005. Insurance losses by driver age. Insurance special report A-70. Arlington, VA.

¹⁷Li, G.; Braver E.R.; and Chen, L-H. 2003. Fragility versus excessive crash involvement as determinants of high death rates per vehicle-mile of travel among older drivers. Accident Analysis and Prevention 35:227-35.

¹⁸Mayhew, D.R.; Simpson, H.M.; and Ferguson, S.A. 2006. Collisions involving senior drivers: high-risk conditions and locations. Traffic Injury Prevention 7:117-24.

¹⁹Braitman, K.A.; Kirley, B.B.; Chaudhary, N.K.; and Ferguson, S.A. 2007. Factors leading to older drivers' intersection crashes. Traffic Injury Prevention 8:267-74.

²⁰Ball, K.; Owsley, C.; Sloane, M.; Roenker, D.; and Bruni, J. 1993. Visual attention problems as predictor of vehicle crashes in older drivers. Investigative Ophthalmology and Visual Science 34:3110-23.

²¹Johnson, C. and Keltner, J. 1983. Incidence of visual field loss in 20,000 eyes and its relationship to driving performance. Archives of Ophthalmology 101:371-75.

²²Owsley, C.; McGwin, G., Jr.; and Ball, K. 1998. Vision impairment, eye disease, and injurious motor vehicle crashes in the elderly Ophthalmic Epidemiology 5:101-13.

²³Braver, E.R. and Trempel, R.E. 2004. Are older drivers actually at higher risk of involvement in collisions resulting in deaths or non-fatal injuries among their passengers and other road users? Injury Prevention 10:27-32.

²⁴Dellinger, A.M.; Kresnow, M.; White, D.D.; and Sehgal, M. 2004. Risk to self versus risk to others: How do older drivers compare to others on the road? American Journal of Preventive Medicine 26:217-221.

²⁵Langford, J.; Bohensky, M.; Koppel, S.; and Newstead, S. 2008. Do older drivers pose a risk to other road users? Traffic Injury Prevention 9:181-89.

²⁶Tefft, B. 2008. Risks older drivers pose to themselves and to other road users. Journal of Safety Research 39:577-82.

²⁷Hennessy, D.F. and Janke, M.K. 2005. Clearing a road to driving fitness by better assessing driving wellness; Development of California's prospective three-tier driving-centered assessment system. Report no. CAL-DMV-RSS-05-215. Sacramento, CA: Office of Traffic Safety, California Department of Motor Vehicles.

²⁸Ball, K.K.; Roenker, D.L.; Wadley, V.G.; Edwards, J.D.; Roth, D.L.; McGwin, G., Jr.; Raleigh, R.; Joyce, J.J.; Cissell, G.M.; and Dube, T. 2006. Can high-risk older drivers be identified through performance-based measures in a Department of Motor Vehicles setting? Journal of the American Geriatrics Society 54:77-84.

²⁹McGwin, G., Jr.; McCartt, A.T.; Braitman, K.A.; and Owsley, C. 2008. Survey of older drivers' experiences with Florida's mandatory vision re-screening law for licensure. Ophthalmic Epidemiology 15:121-27.

³⁰Levy, D.T.; Vernick, J.S.; and Howard, K.A. 1995. Relationship between driver's license renewal policies and fatal crashes involving drivers 70 years or older. Journal of the American Medical Association 274:1026-30.

³¹Nelson, D.E.; Sacks, J.J.; and Chorba, T.L. 1992. Required vision testing for older drivers. New England Journal of Medicine 326:1784-85.

³²Shipp, M.D. 1998. Potential human and economic cost-savings attributable to vision testing policies for driver license renewal, 1989-1991. Optometry and Vision Science 75:103-18.

³³Grabowski, D.C.; Campbell, C.M.; and Morrisey, M.A. 2004. Elderly licensure laws and motor vehicle fatalities. Journal of the American Medical Association 291:2840-46.

³⁴Langford, J.; Fitzharris, M.; Newstead, S.; and Koppell, S. 2004. Some consequences of different older driver licensing procedures in Australia. Accident Analysis and Prevention 36:993-1001.

³⁵Braitman, K.A.; Chaudhary, N.K.; and McCartt, A.T. 1994. Restricted licensing among older drivers in Iowa. Arlington, VA: Insurance Institute for Highway Safety.

³⁶Vance, D.E.; Roenker, D.L.; Cissell, G.M.; Edwards, J.D.; Wadley, V.G.; and Ball, K.K. 2006. Predictors of driving exposure and avoidance in a field study of older drivers from the state of Maryland. Accident Analysis and Prevention 38:823-31.

³⁷West, C.G.; Gildengorin,G.; Haegerstrom-Portnoy, G.; Lott, L.A.; Schneck, M.E.; and Brabyn, J.A. 2003. Vision and driving self-restrictoin in older adults. Journal of the American Geriatrics Society 51:1348-55.

³⁸Janke, M.K. 1994. The mature driver improvement program in California. Transportation Research Record 1438:77-83.

³⁹Kelsey, S.L and Janke, M.K. 2005. Pilot educational outreach to high-risk elderly drivers. Report no. CAL-DMV-RSS-05-213. Sacramento, CA: Office of Traffic Safety, California Department of Motor Vehicles.

⁴⁰McKnight, A.J.; Simone, G.A.; and Weidman, J.R. 1982. Elderly driver retraining. Report no. DOT HS-806-336. Washington, DC: National Highway Traffic Safety Administration.

⁴¹Owsley, C.; McGwin, G.. Jr.; Phillips, J.M.; McNeil, S.F.; and Stalvey, B.T. 2004. Impact of an educational program on the safety of high-risk, visually impaired, older drivers. American Journal of Preventive Medicine 26:222-29.

⁴²Nasvadi, G.E. and Vavrik, J. 2007. Crash risk of older drivers after attending a mature driver education program. Accident Analysis and Prevention 39:1073-79.

⁴³Farmer, C.M. 2006. Effects of electronic stability control: an update. Traffic Injury Prevention 7:319-24.

⁴⁴Bagdade, J.S. 2004. Low cost intersection improvements reduce crashes for senior drivers. 2004 ITE Annual Meeting and Exhibit Compendium of Technical Papers (CD-ROM). Washington, DC: Institute of Transportation Engineers.

⁴⁵Retting, R.A.; Persuad, B.N.; Gardner, P.E.; and Lord, D. 2001. Crash and injury reduction following installation of roundabouts in the United States. American Journal of Public Health 91:628-31.

⁴⁶Retting, R.A.; Kyrychenko, S.Y.; and McCartt, A.T. 2007. Long-term trends in public opinion following construction of roundabouts. Transportation Research Record 2019:219-24.

⁴⁷Lord, D.; Van Schalkwyk, I.; Chrysler, S.; and Staplin, L. 2007 A strategy to reduce older driver injuries at intersections using more accommodating roundabout design practices. Accident Analysis and Prevention 39:427-32.

⁴⁸Ritter, A.S.; Straight, A.; and Evans, E. 2002. Understanding senior transportation: report and analysis of a survey of consumers age 50+. Washington, DC: American Association of Retired Persons.