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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
167 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).
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.
169 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.
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.)
171 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).
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.)
173 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
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
175 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
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.
177 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
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).
179 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).
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).
181 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.
MANAGING SPEED 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. REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Transportation Officials ECMT European Conference of Ministers of Transport
183 Other Speed Management Strategies FHWA Federal Highway Administration GAO General Accounting Office NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration TRB Transportation Research Board AASHTO. 1994. A Policy on Geometric Design of Highways and Streets. Washington, D.C. AASHTO Journal. 1997. Hearing Addresses Aggressive Driving. Vol. 97, No. 29, July 18, pp. 79. Alink, G.M.M., and N. Otten. 1990. Das Fahrverhalten an Ortseinfahrten--eine Validitätsstudie. Im: Forschungsinstrument Fahrsimulator, Report 11, Schriftenreihe der Daimler-Benz AG. Brindle, R. 1986. The Relationship Between Traffic Management, Speed and Safety in Neighborhoods. In Living With Traffic, Special Report 53, Australian Road Research Board, Victoria, pp. 217231. Brownell, K., G. Marlatt, et al. 1986. Understanding and Preventing Relapse. American Psychologist, Vol. 41, pp. 765782. Casey, S.M., and A.K. Lund. 1993. The Effects of Mobile Roadside Speedometers on Traffic Speeds. Accident Analysis and Prevention, Vol. 25, No. 5, pp. 627634. Comte, S., A.Várhelyi, and J. Santos. 1997. The Effects of ATT and Non-ATT Systems and Treatments on Driver Speed Behaviour. MASTER Working Paper R. 3.1.1. Managing Speeds of Traffic on European Roads, Aug. DeJong, W. 1991. On the Use of Mass Communications To Promote the Public Health. In Surgeon General's Workshop on Organ Donation: Background Papers. Office of the Surgeon General, U.S. Department of Health and Human Services, Rockville, Md. DeJong, W., and C.K. Atkin. 1995. Review of National Television PSA Campaigns for Preventing Alcohol Impaired Driving, 19871992. Journal of Public Health Policy, Vol. 16, No. 1, Spring, pp. 5980. Dudek, C.L. 1997. NCHRP Synthesis of Highway Practice 237: Changeable Message Signs. Transportation Research Board, National Research Council, Washington, D.C., 47 pp. Eberhard, J.W. 1996. Safe Mobility for Senior Citizens. IATSS Research, Vol. 20, No. 1, pp. 2937. ECMT. 1996. Speed Moderation. Organisation for Economic Cooperation and Development. OECD Publications Service, Paris, 86 pp. Ewing, R., and C. Kooshian. 1997. U.S. Experience with Traffic Calming. ITE Journal, Vol. 67, No. 8, Aug., pp. 2833. Fambro, D.B., K. Fitzpatrick, and R.J. Koppa. 1997. NCHRP Report 400: Determination of Stopping Sight Distances. Transportation Research Board, National Research Council, Washington, D.C. Farquahar, J.W. 1978. The Community-Based Model of Life-Style Intervention Trials. American Journal of Epidemiology, Vol. 108, pp. 103111. FHWA. 1988. Manual on Uniform Traffic Control Devices. U.S. Department of Transportation.
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