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5
Other Speed Management
Strategies
Statistics prove
Near and far
That folks who
Drive like crazy
--Are
Burma Shave (Rowsome 1965)
Speed limits are one of the oldest strategies for controlling vehicle
operating speeds, but they are not effective in all driving situations. For
example, speed limits are frequently violated on local streets in urban
areas, where the level of enforcement required to achieve compliance
with posted speed limits using traditional enforcement methods is pro-
hibitively expensive. In this chapter, alternative methods for control-
ling speeds are briefly considered. Most topics have been covered
extensively elsewhere. The approaches discussed here include highway
166
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Other Speed Management Strategies
design, infrastructure improvements, and traffic control; intelligent
vehicle- and highway-related technologies; and interventions for spe-
cial populations, particularly older drivers and new teenage drivers.
ROADWAY DESIGN, INFRASTRUCTURE
IMPROVEMENTS, AND TRAFFIC CONTROL
Approaches that fall under this category are focused on controlling
driving speeds by changes in roadway design, physical changes to the
roadway, and traffic operations rather than by behavioral approaches
such as enforcement or public education.
Designing Roads To Manage Speed
The traditional approach to designing a new road is to define the
function of a facility (e.g., through travel, distribution, access) and its
expected level of service (AASHTO 1994). These characteristics, in
turn, guide the choice of a design speed, which governs selection of
horizontal and vertical elements of new roads--sharpness and extent
of banking of horizontal curves and rate of grade change of vertical
curves--as well as stopping sight distances and intersection sight dis-
tances (AASHTO 1994). In contrast, speed limits, particularly speed
limits in speed zones, are often based on driver operating speeds (e.g.,
85th percentile speeds), which, in turn, affect the timing of traffic
signals (FHWA 1988) and other operational considerations. These
different procedures can lead to inconsistencies among design speeds,
speed limits, and driver operating speeds. Such differences are not
necessarily cause for alarm. Design criteria have considerable built-in
safety margins.1 Hence it may be appropriate to travel at speeds
1 Design criteria are often based on worst-case scenarios and performance characteris-
tics of older vehicles (e.g., locked-wheel braking on wet pavements) (Krammes et al.
1996, 14). In addition, many highway features are constructed with more than mini-
mum design values so that the design speed may actually apply to only a small num-
ber of critical features on a road segment. As a result, the design speed of a highway is
likely to understate the "maximum safe speed" over much of its length (Krammes et al.
1996, 14).
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MANAGING SPEED
168
higher than the design speed on a particular highway section.
However, the dispersion in traffic speeds--a contributing factor to
crash involvement--appears to be lowest when the difference
between design speed and the posted speed limit is small (Garber and
Gadiraju 1988, 2325).
An alternative design approach that attempts to achieve greater
consistency among design speeds, actual driving speeds, and posted
speed limits is under development in the United States. The idea is
to design roads to ensure that driver operating speeds are consistent
with a target operating speed. Roadway geometry is commensurate
with this target speed and, thus, is more consistent with motorists'
expectations of appropriate speeds for conditions (Poe et al. 1996,
2-1). Highway geometric design procedures in Europe and Australia
currently incorporate predicted vehicle operating speeds as an impor-
tant determinant of highway design (Poe et al. 1996, 2-1).2
The key to the approach is the accurate prediction of target oper-
ating speeds. Thus, research in the United States is currently focused
on development of models for predicting expected speeds as a func-
tion of roadway geometry, land use, and other traffic elements (Poe et
al. 1996, xix).3 The methodology presented by Poe et al. considers the
relationship between vehicle operating speeds and roadway geomet-
ric design elements. Model development efforts are focused on
higher-speed, two-lane rural highways where inadequate consistency
and continuity of design contribute to wide dispersions in driving
speeds and increased crash risk.4 Models are also being developed for
2 The Netherlands has embarked on a comprehensive program to rationalize its entire
road system to bring road function, use, and vehicle travel speeds into greater harmony
(see discussion in Chapter 3 under the section "Application of Speed Limits").
3 The Federal Highway Administration (FHWA) is sponsoring research on a Design
Consistency Evaluation Module as part of a comprehensive effort to develop an
Interactive Highway Safety Design Model that would enable highway designers to
consider safety systematically in developing and evaluating cost-effective highway
design alternatives (Paniati and True 1996, 55).
4 In addition to the FHWA-sponsored research to develop a computer tool, a National
Cooperative Highway Research Project (15-17) is under way whose objective is to
develop guidelines that designers can use to improve the geometric design consistency
of roadway features on higher-speed, nonurban, two-lane roads.
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Other Speed Management Strategies
low-speed urban streets where driving speeds often exceed desired
levels, particularly where the roads are shared with vulnerable pedes-
trians and bicyclists (Poe et al. 1996; Tarris et al. 1996). Poe et al.
(1996, 13-3) found that driver operating speeds on urban streets are
affected by such design features as roadway alignment (i.e., how
straight or curving the road is) and lane width. Thus, curving road-
ways and narrower lane widths on residential streets could help
achieve desired lower driving speeds.
The effort to achieve greater congruence between highway design
and driver expectations of appropriate operating speeds clearly has
potential to improve safety. However, more research, validation of
model results, and better understanding of the safety benefits of
alternative designs are required before the approach can be adopted
as standard design practice.
Traffic Calming
"Traffic calming" refers to a variety of physical measures to reduce
vehicular speeds, primarily in residential neighborhoods. The idea
originated in Europe, where the basic objective was to achieve calm,
safe, and environmentally improved conditions on local streets
(Pharoah and Russell 1989, 5). Some of the best-known and earliest
examples of traffic calming were the Dutch "woonerf " schemes of the
early 1970s, which reduced traffic speeds by the use of design treat-
ments that aimed to give equal priority to pedestrians and other non-
motorized road users on neighborhood streets (Pharoah and Russell
1989, 4). Since that time, the concept has spread to other European
countries, Australia, and the United States.
A primary reason for the approach is concern for pedestrian and
bicycle safety on local streets. The risk of injury and death for pedes-
trians struck by a vehicle rises sharply as vehicle speed increases
above very low impact speeds.5 Thus, keeping speeds appropriately
low is a priority on streets that are shared with pedestrians and other
vulnerable road users. The ineffectiveness of speed limits in these sit-
5 See relevant studies reviewed in Chapter 2 and Appendix B.
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MANAGING SPEED
170
uations and the high cost of enforcement have led some communities
to adopt traffic calming measures that physically constrain vehicle
speeds.
Traffic calming treatments include measures to reduce vehicle
speeds by narrowing the roadway and changing the path of the vehi-
cle with roundabouts and traffic circles, widened sidewalks, raised
median strips, chokers, and chicanes (Figure 5-1). Measures that
make higher speeds uncomfortable--speed humps, raised intersec-
tions, and, to a lesser extent, rumble strips--are also common. Traffic
calming treatments can be applied singly (e.g., speed humps on indi-
Figure 5-1 Examples of selected traffic calming techniques (Ullman
1996, 112; Ewing and Kooshian 1997, 2833). (Photographs reprinted
from ITE Journal, Vol. 67, No. 8, Aug. 1997, with permission.)
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Other Speed Management Strategies
vidual streets) or in combination as part of an areawide strategy. They
can range in expense from a speed hump, which costs $1,500 to
$1,700, to traffic circles at local street intersections, which cost
approximately $10,000 (Loughery and Katzman 1998, 14).
In the United States, traffic calming treatments are being adopted
primarily on low-speed residential streets, although more compre-
hensive woonerf-type schemes have been undertaken in a few cities.
Traffic calming is not considered suitable for urban arterial streets,
which serve commuter and commercial traffic and carry emergency
vehicles.6 Although not widely used, traffic calming techniques are
also appropriate in transition areas. For example, "gateway" treat-
ments--a combination of road surface treatments and vertical ele-
ments, such as trees and lamp standards, to create the impression of
passing through a narrowed entrance--can be used to alert drivers on
rural roads to adapt their speeds as they approach villages or more
built-up suburban and urban areas.7
Many studies have documented the speed and traffic-reducing
effects of traffic calming (Pharoah and Russell 1989; Fildes and Lee
1993, 6973; Loughery and Katzman 1998, 23). However, speed
and traffic reduction on a treated street can divert the traffic and
related speeding problems to neighboring streets. The speed hump
program evaluation in Montgomery County, Maryland,8 for exam-
6 Concern has also been raised concerning response times of emergency vehicles on
traffic-calmed residential streets. A recent study of the effect of an extensive speed
hump program on residential streets in Montgomery County, Maryland, found that
emergency response time was slowed somewhat by the presence of speed humps. Every
five speed humps had the effect of increasing the distance between the station and the
incident by 1/4 mi (0.4 km) compared with a response route without humps and
assuming a travel speed of 25 mph (40 km/h) (Loughery and Katzman 1998, 56,
Appendix E).
7 Critiques of gateway schemes, particularly those aimed at reducing speed on rural
roads at entrances to villages, suggest that their success depends on stringent physical
measures to reduce speeds that must be applied at regular intervals to sustain speed
reductions (Alink and Otten 1990 and Wheeler et al. 1994 in Comte et al. 1997,
2324).
8 The county has an extensive speed hump program. Since 1994, 1,150 speed humps
have been installed on 300 county streets at an average cost of $1,650 per hump
(Loughery and Katzman 1998, 1).
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MANAGING SPEED
172
ple, found evidence of traffic diversion on parallel streets without
speed humps (Loughery and Katzman 1998, 23). Of course, the net
effect depends on the number of streets treated and the availability of
parallel routes.
Many studies (Zein et al. 1997; Pharoah and Russell 1989; Brindle
1986; Fildes and Lee 1993) have also noted safety benefits of traffic
calming, citing large reductions in crash frequency and injury sever-
ity, although safety is not the sole objective of neighborhood traffic
calming projects. In theory, lowering vehicle speeds should reduce
the severity of crashes, particularly those involving pedestrians. It is
not as clear to what extent lower speeds on residential streets can
reduce crash likelihood. The difficulty in studying these effects arises
from the scattered pattern of crashes in residential areas and the small
size of "before and after" data sets that limit statistical analysis
(Pharoah and Russell 1989, 45).9 In addition, just as traffic can
migrate from treated to nontreated streets, so can crashes.
Application of traffic calming techniques on an areawide basis should
address traffic diversion. Reviews of low-speed zones in urban areas
bear out this contention; speeds and crashes have been successfully
reduced within the zones.10 However, it is difficult to establish a
direct causal link between speed reduction and crash reduction
(Brindle 1986, 228) and to isolate the effects of traffic calming treat-
ments because many of these areawide schemes have been accompa-
nied by complementary policies, such as publicity campaigns and
increased enforcement.
9 The results of "before and after" crash data on traffic-calmed streets in Montgomery
County provide some indication of the difficulty of measuring safety effects. The
report noted that, of the 27 representative streets evaluated, 9 experienced a decrease
in crashes after speed humps were installed and 2 experienced an increase. Where
increases were reported, the number of crashes increased from zero to one. Six streets
reported no change, but on five there were no crashes at all; the sixth street experienced
only one crash. The 10 remaining streets had no available data (Loughery and
Katzman 1998, 34).
10 There is some evidence, however, that part of the decrease in crashes is due to the
decrease in traffic volumes in the zones and diversion of traffic outside the zones. The
diversionary effect needs to be studied further to assess the net safety effects of urban
speed zones. (See discussions in Chapter 3 and Appendix C.)
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Other Speed Management Strategies
Traffic Control
Operational measures can be used to slow traffic. In neighborhoods, mul-
tiway stop signs, traffic signals, turn prohibitions, and one-way streets
have been used to manage speed. Because they require driver compliance,
many operational measures (e.g., stop signs) are less effective than their
physical counterparts in reducing driving speeds (Ullman 1996, 114).
If properly set and coordinated with posted speed limits, traffic
signals can be an effective way of controlling speeds. Considerable
advances have been made in designing and implementing computer-
based signal control systems (GAO 1994). Improving signal timing
can reduce vehicle stops and hence lessen the opportunities for rear-
end collisions. It also encourages more uniform speeds. Mistimed
signals can encourage speeding to avoid yellow or red lights and
widen speed dispersion.
Perceptual Countermeasures
An alternative to physical changes to the road is less intrusive and
lower-cost design treatments, known as perceptual countermeasures,
which alter how drivers perceive the road or roadside (Fildes and
Jarvis 1994, 1). A typical example is a patterned road surface (trans-
verse road marking) that gives the appearance that one is traveling
much faster than would be the case without the treatment. A range
of other measures is available, including center and edge-line treat-
ments; lane-width reductions; curvature enhancements; and delin-
eators, guideposts, and chevrons. Most of these measures are low in
cost, although some require continued maintenance to be effective.
Thus, they may be appropriate in locations where more expensive
treatments cannot be justified. However, their long-term effective-
ness in reducing speeds is not well established and often appears to
be site dependent (Fildes and Lee 1993, 77).
VEHICLE- AND HIGHWAY-RELATED TECHNOLOGIES
As vehicles have become more electronically advanced and improved
technologies have enabled provision of real-time information
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MANAGING SPEED
174
between the highway and the vehicle, the groundwork has been laid
for more sophisticated speed management strategies and more auto-
mated speed control measures. Many of these measures are encom-
passed under the Intelligent Transportation Systems program, whose
goal is the improved safety and efficiency of highway travel. Some of
these technologies are already in use. Others require more research
and demonstration to ensure their reliability and public acceptance.
Vehicle-Related Technologies
Some motorists underestimate or misjudge their driving speed. With
older vehicles, drivers had more physical cues about speed, including
the tilting motion and sound of the tires when negotiating a sharp
curve and the noise of the road when traveling at higher speeds
(Comte et al. 1997, 39). Today, improved vehicle handling, high-
performance tires, and air-conditioning systems mute these cues.
Technologies are being developed to provide more information and
feedback to the driver about driving speeds and, in the longer term,
to create "intelligent" vehicle control systems.
Many such technologies are well along in development. For exam-
ple, heads-up display speedometers that provide continuous speed
information to drivers in their normal fields of view, rather than
requiring drivers to look at the dashboard periodically to check
speed, are available (Comte et al. 1997, 39). Speed checkers--elec-
tronic devices mounted on the dashboard that are activated by road-
side transmitters at mileposts or on speed limit signs--have been
tested for their potential to warn drivers that they are exceeding legal
speed limits. Of course, user acceptance is likely to be better if the
device is activated only in highly hazardous locations (Comte et al.
1997, 40). Emergency warning systems are also being developed. For
example, sensors on the front of the vehicle could detect when a vehi-
cle is closing too fast on the vehicle immediately ahead and warn the
driver when the distance equals a predefined limit for the travel speed
(TRB 1998, 3233). A curve-approach warning system, using road-
side communication beacons to provide information about roadway
geometry, could alert drivers to sharp curves, warning them if the
vehicle is approaching at excessive speed (TRB 1998, 33). This type
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Other Speed Management Strategies
of warning system could be particularly effective in forestalling
speed-related, run-off-the-road crashes. However, commercialization
and broad driver acceptance of many of these speed-related informa-
tion systems depend on resolution of human factors issues, such as
driver distraction and information overload.
Vehicle control technologies offer another level of sophistication
in speed management. Conventional cruise-control systems, which
are mainly used in freeway driving, already enable drivers to establish
and maintain a fixed vehicle speed. More advanced adaptive cruise-
control systems, which are under development by some automobile
manufacturers and their suppliers, would use forward-looking sen-
sors and adjust vehicle speeds automatically to maintain a safe fol-
lowing distance from the vehicle ahead (TRB 1998, 34). Key
concerns are reliability and the pros (e.g., crash avoidance) and cons
(e.g., driver inattentiveness) of automating critical driving tasks. Of
course, fully developed collision avoidance systems would involve
lane-departure avoidance systems as well as frontal-collision avoid-
ance systems.
Speed governors offer a solution for limiting the maximum speed
of a vehicle. Speed governors are required on heavy trucks that oper-
ate in countries that are part of the European Union (ECMT 1996,
32). Some U.S. trucking companies also use speed limiters, although
increasingly sophisticated truck engines enable speeds to be con-
trolled electronically. The primary reasons for using speed governors
on heavy vehicles are fuel efficiency, safety, and equipment wear. In
the United States, the speed governor or engine is usually set at the
speed that provides maximum fuel efficiency, which generally falls
below most current maximum speed limits on major highways. The
use of speed limiters on passenger vehicles has been tested in Europe
(Comte et al. 1997, 4548), but issues of driver control, system cost--
and, above all, consumer acceptance--are likely to preclude their
widespread use in the foreseeable future.
Other speed-limiting approaches involve "smart cards," which
combine vehicle functions with a driver's license and allow variable
speed governing depending on the driver and the situation. For
example, the smart card could prevent teenage drivers with provi-
sional licenses or repeat offenders of drunk driving and speeding
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MANAGING SPEED
176
from exceeding certain speed thresholds. In the former case, the
speed could be set by a parent; in the latter, by the courts.
Highway-Related Technologies
Road-based technologies use electronic capabilities to provide drivers
with information about upcoming roadway conditions. One of the
most commonly available technologies is variable message signs,
which can be used for speed control. For example, a recent survey of
permanently mounted changeable message sign usage in the United
States and one Canadian province found the following speed-related
uses: incident and traffic management, fog warnings, and warnings of
other adverse weather and road conditions (Dudek 1997, 10). The
effect of these signs on motorist behavior has not been studied exten-
sively, and the studies that have been conducted tend to be out of date
(Dudek 1997, 46). Use of variable message signs in Europe, particu-
larly to display appropriate speed limits, appears to suffer from the
same limited time- and distance-halo effects as traditional enforce-
ment measures (Comte et al. 1997, 31).
Variable speed limits represent a more sophisticated use of variable
message signs to convey information to drivers about appropriate
speed limits. Variable speed limits are not in wide use on U.S. high-
ways today. Where they do exist, their primary function is to provide
weather advisories and appropriate speeds for hazardous conditions.
Variable speed limits have been used more extensively in Europe,
particularly on major motorways, for general speed management.11
They are especially well suited to address temporal changes in traffic
volumes, speed, and density on urban Interstate highways. More
experience is needed concerning the efficiency gains and safety ben-
efits of these systems. However, even if the results are highly positive,
system costs are likely to limit their use to major highways.
Another road-based approach to managing speed is to provide driv-
ers with direct feedback about their driving speeds through the use of
mobile roadside speedometers. The devices usually include a speed
11For more detailed information on this experience, see discussions in Chapter 3 and
Appendix D.
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Other Speed Management Strategies
limit sign, a Doppler radar emitter and receiver to measure speeds,
and a changeable message sign that displays the speed of the
approaching vehicle to the driver (Casey and Lund 1993, 627). Local
jurisdictions are experimenting with these devices to supplement tra-
ditional enforcement measures in problem speed locations on city
streets, in neighborhoods, and in school and work zones.12 An eval-
uation of the effectiveness of roadside speedometers under several
controlled deployment strategies (e.g., varied, intermittent, and con-
tinuous deployment, each with and without enforcement) found that
the speedometer's presence reduced average traffic speed, especially
the speeds of those drivers exceeding the speed limit by at least 10
mph (16 km/h), in the vicinity of the device and short distances
downstream; the device was particularly effective in school zones
(Casey and Lund 1993, 627). However, the effectiveness was clearly
linked with enforcement or implied enforcement, a finding of many
other studies (Comte et al. 1997, 3236). Unless coupled with peri-
odic enforcement, roadside speedometers appear to be ignored by
motorists whether the deployment is continuous or intermittent
(Casey and Lund 1993, 634).
Fully Automated Vehicle and Highway Systems
Fully automated highways, which would combine many of the vehi-
cle- and highway-related technologies described previously, would
fully control speed essentially by taking the driving task away from
the individual driver. To obtain the full efficiency benefits of close
headways and high travel speeds, fully automated travel lanes would
be required with traffic moving in coordinated platoons of fully auto-
mated vehicles (TRB 1998, 3536.). A public demonstration of sev-
eral automation technologies was held in San Diego, California, in
August 1997, but prototype development, much less full deployment,
of an automated highway system will not be realized any time soon.13
12 Some jurisdictions are using the roadside speedometer readings to target enforce-
ment by location and time of day.
13 In fact, the U.S. Department of Transportation has shifted its research priorities to
encourage development and deployment of nearer-term advanced vehicle control and
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MANAGING SPEED
178
Even if reliability and liability issues could be resolved, the large
investment costs will severely limit deployment of such a system to
all but a few sections of major highways where the efficiency and
safety gains might justify the expense.
SPECIAL DRIVING POPULATIONS
The problem of speeding or driving too fast for conditions is not
confined to any one driving group, but certain groups of drivers--
older drivers and younger drivers in particular--have special problems
with speed. Aggressive drivers could also be included, but aggressive
driving14 has only recently been identified as a traffic safety problem
and has not yet received much analytic review. In this section, the
speed-related problems of older and younger drivers are identified and
strategies to manage them are reviewed.
Older Drivers
Older drivers are one of the fastest-growing segments of the driving
population. The 65 and older age group, which numbers about 34
million today, will exceed 50 million by 2020, accounting for approx-
imately one-fifth of the driving age population in the United States
(FHWA 1997, v).
Many older drivers have reduced capability to handle speed
because of declining performance in visual, cognitive, and motor
tasks that accompany aging (TRB 1988, 72). Vision, particularly
night vision, becomes poorer and reflexes slower, so that older drivers
generally have slower perception-reaction times (TRB 1988, 72).
Older drivers tend to compensate for these changes by restricting
their night driving and by driving slower than the prevailing traffic,
driver assistance features. This new Intelligent Vehicle Initiative, which deemphasizes
the earlier target of fully automated driving, is focused on improving highway safety
(TRB 1998, 5).
14 Aggressive driving, or "road rage" as it is more commonly known, refers to driving
behavior that endangers or is likely to endanger people or property (AASHTO Journal
1997, 8).
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Other Speed Management Strategies
which may increase their risk of multivehicle crash involvement.15 If
a crash occurs, older persons are more likely to be injured because of
their frailty (Mackay 1988).
Addressing the speed-handling capabilities of older drivers is not
easy. In recent years, considerable research has been conducted on the
question of whether highway design is sufficiently sensitive to
assumptions about driver performance, particularly the performance
of older drivers. Perception-reaction time is a key concept in models
of driver behavior and highway design that underlie many highway
design criteria. Current American Association of State Highway and
Transportation Officials (AASHTO) design criteria assume a 2.5-s
perception-reaction time for sudden stopping when the driver must
brake in reaction to an unexpected obstacle (Lerner et al. 1995, 3)16
and 2.0 s for estimating appropriate sight distances at intersections
(AASHTO 1994, 704). Age differences were observed in experi-
mental situations, with somewhat longer perception-reaction times
for older drivers, but these differences are encompassed by
AASHTO design criteria. No major changes in design parameters
were recommended (Lerner et al. 1995, 9597; Fambro et al. 1997).
Previously discussed technological advances in driver information
systems and vehicle control technologies could enhance the ease and
speed with which information is provided to the driver and simplify
some driving tasks. These improvements would benefit all drivers,
but could especially assist older drivers if the technologies are intro-
duced in ways that do not distract drivers or overload their ability to
process information.
Other suggestions for addressing the speed-handling capabilities of
older drivers as well as their general driving skills include driver train-
ing programs especially tailored for older drivers and a graded licens-
ing system for older drivers, which would restrict driving on the basis
of the individual's capabilities. The effectiveness of training programs
in improving the performance of older drivers has not been estab-
15 See the reviews of studies linking crash involvement with deviation from average
traffic speeds in Chapter 2 and Appendix B.
16 This time consists of two components: 1 s for perceiving the situation and initiat-
ing action and 1.5 s for braking (TRB 1988, 63).
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MANAGING SPEED
180
lished (McKnight 1988, 117). Technical issues, such as developing
adequate licensing test procedures, and more general issues, such as
age discrimination and mobility concerns, are major roadblocks to the
introduction of modified licensing procedures for older drivers (TRB
1988, 73; Eberhard 1996, 36).
Younger Drivers
Although the U.S. population is aging, nearly a 20 percent increase in
the population of 16- to 24-year olds is projected--from 36 million to
43 million potential drivers by 2020 (NHTSA 1997, 4). California esti-
mates a one-third increase in its population of 15- to 19-year-olds over
the next 10 years alone, the result of delayed childbearing by the Baby
Boom generation, high levels of immigration, and high birth rates in
parts of the population (Highway and Vehicle Safety Report 1998, 23).
In marked contrast to older drivers, younger drivers' problems with
speeding are related to their propensity to take risks and their driving
inexperience. Both characteristics can cause them to drive at speeds
inappropriate for conditions.
Some states have enacted graduated licensing systems as one way
to limit high-risk youthful driving behaviors, including speeding.
The idea is to restrict the time and manner of driving in stages to
allow beginning drivers to acquire on-the-road experience in lower-
risk settings before obtaining a regular, unrestricted license (Status
Report 1996, 1).17 The emergence of graduated licensing systems in
the United States provides an opportunity to revamp driver educa-
tion programs, which, according to many studies, have fallen far short
of their objective to reduce the crash experience of young drivers
(Status Report 1997, 1).
Education is often recommended as a significant method of reduc-
ing risk behavior (DeJong 1991; DeJong and Atkin 1995;
McMahaon 1986; Brownell et al. 1986). Many public health pro-
17 Typical elements of a graduated licensing system include a mandatory supervised driv-
ing period, night driving curfew, limits on teenage passengers riding with a beginning
driver, a freeway driving restriction, and a lower blood alcohol concentration thresh-
old for teenagers than for adults (Status Report 1996, 12).
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Other Speed Management Strategies
grams intended to promote healthy choices and reduce risky ones
have included an education component. Efforts in smoking cessa-
tion, nutrition, exercise, pregnancy prevention, and substance abuse
are examples. It is therefore likely that education should be consid-
ered as a component in working with driver groups, such as teenage
drivers, who are at higher risk of speed-associated traffic injury, to
increase their compliance with posted speed limits or reduce inap-
propriate speeding behavior. Research on education in other risk
reduction situations, however, indicates that education intended to
frighten individuals into changed behavior has only limited, short-
term efficacy, and that education alone is almost never sufficient to
achieve long-term behavior change ( Job 1988; Montezeri and
McEwan 1997). It must be accompanied by other approaches that
increase awareness of vulnerability and provide social support, such as
peer group approval for the desired behavior (Farquahar 1978).
Both younger and older drivers have special, identifiable problems
handling speed. However, finding effective strategies to address
their speed-related problems is difficult and represents a significant
challenge.
SUMMARY
In this chapter, several alternatives to speed limits for managing driv-
ing speeds have been considered. Road redesign--and to an even
greater extent traffic calming--attempt to physically constrain driv-
ing speeds to desired levels. Traffic calming can be an effective strat-
egy for reducing speed on some residential streets, but it is not
considered suitable for major urban roads. Designing roads so that
the resulting roadway geometry is more consistent with motorists'
expectations of appropriate driving speeds has promise for existing as
well as new highways, but more research is needed to determine the
safety benefits of alternative designs. Preliminary findings indicate
that, on low-speed urban streets, use of an operating speed model in
the design process could bring actual speeds closer to intended
speeds. Even if design procedures can be modified, however, road
redesign is a long-term strategy because of the extent of highway
mileage in the United States and the pace and cost of rehabilitation.
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182
Technological advances to provide more "intelligent" vehicles and
highways offer another approach. New ways of communicating
information to the driver about appropriate driving speeds are under
development, and advances in vehicle control technologies should
enable automation of some speed-related driving functions.
Introduction of these technological advances awaits resolution of
human factors concerns, such as driver distraction and information
overload, and--with more automated systems--issues of reliability,
liability, driver control, and acceptance. Some systems may become
commercially available shortly, but it will be several years before they
become standard equipment on all motor vehicles.
The most challenging approaches are those that attempt to change
driver behaviors and attitudes toward speeding. Special populations,
particularly older drivers and young drivers, have been identified as
having particular, though different, problems with speeding. As the
experience with other risky behaviors such as drinking and driving or
smoking has shown, attitudinal changes are possible. They require
awareness and understanding of risk and a long time frame. In the
case of speeding, aging of the population and continued or more fre-
quent aggressive driving could result in more negative attitudes
toward speeding and greater compliance with speed limits than are
evident today. Of course, if vehicles and roads become safer, motorists
could favor higher limits, at least on the safest roads.
The approaches identified in this chapter offer a range of methods
for controlling driving speeds. Their use is often limited to certain
types of roads or settings (e.g., residential streets). For the foreseeable
future, their most likely application is to complement and enhance
rather than to supplant speed limits. For the longer term, they repre-
sent important areas of innovation and opportunity that bear watch-
ing and evaluation.
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TRB Transportation Research Board
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Representative terms from entire chapter:
traffic calming
