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|Federal Highway Administration > Publications > Public Roads > Vol. 70 · No. 1 > Senior Mobility Series: Article 4 - Marking the Way To Greater Safety|
Publication Number: FHWA-HRT-2006-005
Senior Mobility Series: Article 4 - Marking the Way To Greater Safety
by Gene Amparano and David A. Morena
Bigger and brighter signs, more conspicuous signals, and wider stripes are among the innovations making highways safer for older road users.
The older driving population in the United States has grown continually and is expected to increase even more as the baby-boom generation reaches retirement. What transportation impacts can be expected as a result of the aging baby boomers? The capabilities essential for safe driving — visual, cognitive, and physical — undergo changes with age. These changes can influence the safety of drivers, passengers, and pedestrians.
For example, visual changes affect the distance at which older drivers can see and recognize the writing on signs and may make it more difficult for them to detect pavement markings. Physical changes influence reaction times and restrict physical movement in seniors. These types of changes present transportation agencies with the challenge of finding and implementing solutions to help seniors maintain safe mobility in their communities.
The U.S. Department of Transportation and State departments of transportation (DOTs) recognize the importance of continued mobility to seniors. Several State DOTs already have taken specific steps to improve delivery of enhanced visual information that is helpful for maintaining safety for aging drivers. For instance, some States have broadened and brightened pavement markings to better delineate lanes and road edges. Others have made signs and signals more conspicuous.
"Safety is a bunch of little things, and the key is to come up with a whole menu of remedies that collectively will cut crashes and fatalities," says John Friend, engineer of delivery for the Michigan Department of Transportation (MDOT). "I know in Michigan we have taken many approaches. Our fatality rate is going down."
Whatever modifications are made, they reflect a growing realization that not only seniors but everyone, sooner or later, will benefit from better, safer roadways.
Highway Design Handbook And Workshops
The Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation contains provisions to "carry out a program to improve traffic signs and pavement markings in all States" consistent with the Federal Highway Administration's (FHWA) Highway Design Handbook for Older Drivers and Pedestrians (FHWA-RD-01-103). The handbook provides 109 recommendations for safety enhancement, grouped under five categories: intersections (at-grade), interchanges (grade separation), roadway curvature and passing zones, construction work zones, and highway-rail grade crossings (passive).
Many States have hosted one or more FHWA-sponsored workshops that presented the handbook's recommendations, and Iowa and New Jersey have hosted train-the-trainer sessions. Because of these sessions, Iowa has held several workshops for county and local transportation agencies. New Jersey is planning similar workshops.
It is crucial to recognize that safety and navigational enhancements implemented for older road users should benefit all users as well. Consideration of safety improvements geared for aging drivers therefore should be an integral part of the planning, design, and development phases of all roadway projects. In most cases, the enhancements are a minor part of the overall project cost and are cost effective when compared to the long-term benefits they offer.
Traveling the Nation's roadways can be confusing and challenging for all drivers if routes are not clearly marked or easily understood, especially when the driver is in unfamiliar territory. This challenge can be compounded for an older motorist who might have diminished cognitive or physical abilities. From an engineering standpoint, opportunities to enhance drivers' abilities to detect signs and comprehend sign messages include: sign legibility, placement, brightness (retroreflectivity), and size.
Legibility. Legibility is generally defined as the readability of a particular writing style, or font. Fonts approved for use on highway signs (FHWA's Standard Alphabets) have changed little since the 1960s. Research conducted in the 1990s, however, resulted in a new font, Clearview, that provides faster word recognition at greater distances by optimizing each letter's legibility and by reducing halos around text messages. In the last decade, several indepth studies have shown that the Clearview alphabet's legibility represents a 16-percent improvement in recognition distance by older drivers and a 12-percent increase in legibility for all drivers compared to the existing standard (modified Series E font) for guide signs. Thus, the Clearview font results in faster reading, comprehension, and reaction times for drivers performing required driving tasks. To spread the safety benefits nationwide, FHWA granted interim approval in a September 2004 memorandum for the optional use of the Clearview font for positive guidance on guide signs.
To date, eight States (Arizona, Iowa, Kentucky, Maryland, Michigan, Pennsylvania, Texas, and Virginia) have adopted Clearview font for use on guide signs on all or part of their systems, and nine more States have received FHWA approval to use the Clearview font.
Another approach that States have taken to increase legibility is simply to increase the letter heights on guide and street name signs. The Manual on Uniform Traffic Control Devices (MUTCD) provides the minimum requirements for letter size, and it also states that "the minimum lettering sizes specified herein should be exceeded where conditions indicate a need for greater legibility." Using larger letters could be justified in the States where older drivers exceed 15 percent of the total driving populations. Based on 2003 FHWA data, 26 States exceed this percentage of older driver population.
Several States are using larger letters to enhance legibility for all drivers. For example, Maryland provides 51-centimeter (20-inch) uppercase and 38-centimeter (15-inch) lowercase letters on its guide signs at decision points at exits from freeways. The use of uppercase/lowercase letters also adds to enhanced legibility on guide signs. Also, Toledo, OH, has been using advance street name signs with 36-centimeter (14-inch) letters on many major roads since the 1970s.
Sign Placement. Safe driver responses to road signs depend largely on placement. Signs should be placed at locations that have unobstructed visibility and minimum background clutter. The preferred practice, as encouraged in the MUTCD, is overhead placement at intersection and interchange locations, which optimizes sign visibility.
In some instances, signs can be placed in the driver's direct line of sight. For example, the handbook recommends that a one-way sign at a T-intersection be placed on the far side, directly opposite the center of the approaching lane, directly in line with traffic. The Iowa Department of Transportation (Iowa DOT) places its chevron alignment signs on curves with a similar strategy, lining up the middle chevron sign with the center of the approaching lane. Adjacent chevron signs are installed so that at least two are in view at all times.
"At the first curve we did this, a 3-year before-and-after study found that we had a 25-percent reduction in curve-related crashes by just improving the existing chevron signs," says Tom Welch, Iowa DOT's State transportation safety engineer. In addition, all new warning signs throughout the State will be fluorescent yellow.
Another common placement is to double up on the use of signs, placing redundant ones on the left side of the roadway opposite the primary signs on the right side. Some States are following this practice routinely for advance work zone signing on high-speed roads and for wrong-way signing at freeway ramps. This practice also can be applied more strategically at critical locations. For example, the Pennsylvania Department of Transportation doubled its stop signs at key intersections.
Brighter Sheeting, Bigger Signs. Brighter sheeting materials make signs more conspicuous, especially at locations with high levels of visual "noise," such as guide and regulatory signs, in the background. Research at the University of South Dakota shows that the time needed by older drivers to detect signs in complex backgrounds can be reduced significantly by using super-high-intensity sheeting materials. Research also shows that the detection distance for fluorescent signs is significantly greater than nonfluorescent signs for both younger and older observers, though the older drivers reaped the most benefit. Since the MUTCD adopted the allowable use of fluorescent sheeting, most States are using the fluorescent yellow-green sheeting to increase the conspicuousness of pedestrian and bicyclist warning signing.
Other sign colors such as fluorescent yellow prismatic sheeting are being used by at least five State DOTs on all or some of their warning signs. This practice also is spilling over into work zones, where the vast majority of DOTs are routinely using fluorescent orange sheeting. The use of high-intensity sheeting, considered a best practice from the late 1980s until just a few years ago, was superseded by the use of fluorescent prismatic materials for the background on these signs.
For white-on-green guide signs in use across the country, high-intensity green background sheeting remains the choice of most States, but prismatic sheeting has emerged as the state-of-the-art for the white legend and border. At least six States now require this improved sheeting on all or large portions of their systems. A prismatic white legend's main benefit is the improved retroreflectivity that enhances the legibility of the sign message.
Signs larger than the minimum requirements have become commonplace in many States as a way to increase conspicuousness and legibility distance. Larger signs are especially beneficial for older drivers at night. The Mississippi Department of Transportation (MDOT) has developed a program to systematically upgrade the size of its regulatory signs.
Iowa DOT, as part of its older driver safety program, has added new curve warning and chevron signs and upgraded the size and brightness of the existing signs on curves that have had a high number of crashes.
Other Ways to Increase Sign Conspicuousness
Internally Lit Signs. Internally lit street name signs are becoming more widely used at signalized intersections, especially in urban areas. They are installed as supplements to or replacements for the standard post-mounted street name signs to make them more conspicuous at night. This practice is becoming popular among all jurisdictions — State, city, and county. In addition to illumination, these signs generally include larger lettering: Most have at least a 20-centimeter (8-inch) letter height, some as much as 30 centimeters (12 inches).
In Michigan, MDOT and local agencies within the State have expanded this practice by using internally lit, overhead "case" signs to provide signal-related messages at intersections. A case sign is a hollowed-out cube, with sign messages on one or more cube faces, and a light source in the center of the cube. MDOT is exploring the eventual conversion of the existing incandescent light source to the more energy-efficient light-emitting diode (LED) technology.
Lower Mounting Heights. Since the inception of the interstate system, wrong-way maneuvers on ramps have been a problem for many States. At least three States (California, Idaho, and Virginia) have attempted to address this problem by lowering the mounting height of the wrong-way and do-not-enter signs on their freeway entrance ramps. Lowering the mounting height increases both the daytime and nighttime conspicuousness of the signs, particularly at night, due to the enhanced retroreflectivity of sheeting that is closer in height to a vehicle's headlight.
The California Department of Transportation (Caltrans) began placing its wrong-way and do-not-enter signs at a lower mounting height of 0.6 meters (2 feet) in 1973. Caltrans places the two signs on the same sign post and locates the sign package closer to the exit ramp termini to improve headlight visibility and enable drivers to take avoidance action prior to completing wrong-way moves. This change helped to reduce the frequency of wrong-way movements from 60 per month to less than 2 per month at 90 percent of the identified locations.
The Virginia Department of Transportation conducted similar research in 1980 and adopted the California practice in December 1981. The Idaho Transportation Department has been installing wrong-way signs on exit ramps at a reduced mounting height of 1.2 meters (4 feet) since the mid-1970s. Although these States are employing a lower mounting height for these signs than currently permitted by the MUTCD, the exception here is narrowly defined: The location is low-speed on-ramp, and the targeted driver is a wrong-way driver. States that are considering using this countermeasure are advised to seek approval to experiment from FHWA.
There are many precedents for State-level successes influencing the MUTCD. In the early 1990s, for example, Florida — a State with high concentrations of older drivers — overhauled its signing and pavement markings with older drivers in mind. Among other things, legend sizes and overall sign sizes for stop, yield, and warning signs were increased based on 20/70 visual acuity, and the MUTCD later adopted this standard, according to Gail Holley, program manager of the Florida Department of Transportation's (FDOT) Elder Road User Program.
Flashing Beacons. Many States use flashing beacons in a variety of ways to provide extra notice to drivers. When used with signs, they can be effective in drawing attention to critical warnings and may prompt the desired driver response.
Many States use overhead flashing beacons over the center of intersections with stop control on the minor roads. The beacon flashes yellow to induce caution from approaching mainline traffic and flashes red to the approaching minor-road traffic to support the stop-sign control. The Minnesota Department of Transportation (Mn/DOT) had many of these applications in place but believed the beacons were giving the false perception that all the flashers were red.
For the last 3 or 4 years, Mn/DOT has tried a new strategy at more than 30 intersections: It has removed the four-headed beacon from the center of the intersection and placed a flashing yellow beacon on the appropriate ground-mounted warning sign preceding the intersection on the major road and a flashing red beacon on the minor road stop sign. "We're very pleased with the results so far," says Minnesota State Traffic Safety Engineer Loren Hill. "We haven't had time to do a comprehensive followup, but the early 'after' data shows a reduction in crashes." The effectiveness of this practice currently is being evaluated as part of the FHWA Low Cost Safety Improvements Pooled Fund Study.
Pavement Markings and Other Roadway Delineation
FHWA defines delineation as "one or a combination of devices (excluding guide signs) that regulate, warn, and provide tracking information and guidance to the driver." Delineation guides all motorists, of course, but is especially beneficial to older drivers. Pavement markings in particular can be enhanced to provide better guidance, and they include wider and brighter edge and centerline markings and improvement of wet-night visibility through use of oversized glass beads in paint, raised pavement markers, profile thermoplastic markings, painted rumble strips, and painted curb islands.
Wider Markings. Based on the Texas Transportation Institute's (TTI) 2002 survey findings in The Use of Wider Longitudinal Pavement Markings, 29 out of 50 State DOTs report that they use longitudinal pavement markings wider than the specified 10-centimeter (4-inch) minimum in at least some situations and cite visibility improvement as the primary reason. Most of these States note that they and their drivers are pleased with the results and plan to continue using the wider markings. The only cost incurred is that for extra materials, as the installation time is essentially the same as for narrower markings.
Although there is no conclusive evidence that wider markings reduce crash numbers, indirect measurements from observational field studies have shown that drivers exhibit fewer centerline encroachments, more central vehicle positioning, and less variability in vehicle positioning with 15-centimeter (6-inch) and 20-centimeter (8-inch) edge lines than with 10-centimeter (4-inch) edge lines, according to TTI. This same research cites several benefits in using wider markings, including improved long-range detection under nighttime driving conditions (older drivers benefit the most), improved stimulation of peripheral vision, better lane positioning and other driver performance measures, and greater driver comfort. As mandated by SAFETEA-LU, FHWA is now conducting additional research into the safety benefits of 15-centimeter (6-inch) versus 10-centimeter (4-inch) markings.
The Nevada Department of Transportation leads the Nation in use of the widest markings: It has installed 20-centimeter (8-inch) wide longitudinal pavement markings on all freeway facilities. The South Dakota Department of Transportation installs 20-centimeter (8-inch) edge lines on its two-lane roads having shoulder widths of 0.6 meter (2 feet) or less.
The more common practice, in use by 20 State DOTs and at least 6 toll-road facilities, is to install 15-centimeter (6-inch) wide edge-line and/or centerline pavement markings on all or predetermined portions of their systems. Ten States use the 15-centimeter (6-inch) markings on freeways, interstates, or divided highways. Three States place 15-centimeter (6-inch) markings on edge lines only. Two States use the markings for lane lines only. Four States use the markings throughout their entire systems. Also, some State DOTs are using high-contrast, black-on-white and black-on-yellow markings to increase the conspicuousness of their lane lines and centerlines on light-colored concrete pavements.
In Michigan, MDOT is reporting success and satisfaction with its 2004 move to wider edge lines. "Going from a 4-inch [10-centimeter] wide marking to a 6-inch [15-centimeter] marking costs practically nothing more in terms of material and labor, but the improved visibility is significant," says MDOT's Friend. "We know from the feedback we've had from seniors that the change is appreciated and is making a difference."
Wet-Night Visibility. The effectiveness of longitudinal pavement markings at night is dependent upon their retroreflectivity, which is not difficult to achieve under dry conditions. However, with rain or snow, a thin film of water on a traditional marking causes the reflected light to scatter in all directions, thus reducing the amount of light reflected directly back to the driver. Although national standards do not mandate that pavement markings must perform well in wet conditions, many State DOTs are using a variety of strategies to ensure just that.
Oversized Glass Beads. The majority of State DOTs are using oversized glass beads in their paint markings to improve wet-night recognition of edge and centerline markings. The larger beads enable water to drain more quickly from the marking surface, thus decreasing water film accumulation on the beads and allowing quick recovery of their retroreflective capability.
Raised Pavement Markers. In many States, raised pavement markers (RPMs) are the primary means to improve wet-night visibility of longitudinal markings. For example, FDOT is recognized as a national leader for its practice of installing RPMs at half the spacing distance required by the MUTCD, not only for the overall roadway system but also in work zones. FHWA research shows that RPMs have the following impacts on driver performance:
In States where snow removal using truck-mounted plows is routine, regular RPMs are rarely used. These States use recessed pavement markers milled into the pavement surface, or they resort to other marking strategies.
Profiled Thermoplastic. Some States are using profiled thermo-plastic to enhance the wet-night conspicuousness of pavement markings. This approach consists of a thick, extruded thermoplastic that is then machined to create peaks and valleys in the markings. The peaks — similar to rumble strips — increase the vertical surface of a painted stripe, thereby increasing its retroreflectivity. The valleys provide a path for draining water away from the strip.
Rumble Stripes (Painted Rumble Strips). A newer practice for improving wet-weather visibility of pavement markings is the use of "rumble stripes" — rumble strips topped with 7.6- to 15.2-centimeter (3- to 6-inch) longitudinal paint stripes. Rumble stripes serve two purposes. First, they function as rumble strips and make noise when drivers reach the outside edges of travel lanes. Second, the stripes delineate the edges of the travel lanes with a highly visible longitudinal marking. The vertical face of the painted stripe significantly enhances the retroreflectivity of the strip. In Michigan, MDOT has been a leader in the use of freeway rumble stripes, and the Mississippi and Pennsylvania transportation agencies are recognized leaders in nonfreeway use of rumble stripes.
Painting Intersection Curb Islands. The conspicuousness of curb islands within intersections can be enhanced by treating the front side and horizontal surface with retroreflective paint. Painting increases the contrast of an otherwise dull surface, thus improving delineation. Three State DOTs (Alaska, Iowa, and Wisconsin) routinely paint the curbs at the noses of their median and/or channelizing islands at intersections. A few other DOTs add RPMs to help delineate the noses of the islands. These practices, however rare, are extremely helpful to all motorists as well as older drivers, particularly during inclement weather. The older drivers handbook references studies showing that this countermeasure improves the visual cue of an intersection's geometric features, which is especially beneficial to older drivers. Inability to identify the presence of curbs in dark or dim lighting conditions has been flagged in numerous studies of older drivers as an issue needing further research.
Intersections have long been problematic for older drivers, especially at locations with unprotected left turns. States are adopting several signal-related countermeasures to enhance safety for older drivers; again, there are benefits for the driving population at large.
Signal Location. Probably one of the most overlooked and easiest remedies for making signals more conspicuous is the location of the traffic signal heads. Visual capabilities tend to diminish with age, which includes a reduction in the visual attention window, also known as the useful field of view — the area within which the driver can detect and respond appropriately to information.
Placing or relocating signal heads within that visual attention window at the approach to an intersection provides easier detection and recognition of the signal. This can be accomplished by placing signal heads overhead near the center of the travel lane, preferably one per through lane — the area where drivers focus most of their attention. (Some States prefer to set signal heads slightly offcenter of the travel lane to improve visibility at locations with high truck volumes.) Iowa and Minnesota have adopted policies requiring one signal head per through lane, centered over the travel lane. This practice is expanding into various municipalities as well, such as Kansas City, MO; Las Vegas, NV; and Richmond, VA.
Supplemental Signal Heads. In addition to optimizing placement of the primary signal heads, many States use supplemental signal heads to improve the likelihood that motorists will see and react properly to the signal. For example, Caltrans routinely adds 3-meter (10-foot) high, post-mounted signals at far-left and far-right locations to assist turning traffic and improve signal visibility for vehicles whose view may be obscured by trucks or other high vehicles in front of them. At least six States (Arizona, California, Illinois, Minnesota, Nevada, and Wisconsin) systematically provide motorists with two left-turn signal heads, one more than standard.
Signal Head Conspicuousness. According to current standards, engineers can use signal heads having either a 20-centimeter or 30-centimeter (8-inch or 12-inch)-diameter signal lenses. Replacing the smaller lenses with the larger ones increases the conspicuousness of incandescent signals by a factor of four. This practice is recommended in the older drivers handbook, and many States have adopted it.
A newer approach taken by many States is the use of LED signals. LEDs are becoming widely used because they improve signal conspicuousness and offer the following additional advantages over incandescent signals:
Based on these advantages, several States have developed, or are developing, aggressive programs and policies to replace their incandescent signal heads with LEDs. California estimates that 80 percent of its 30-centimeter (12-inch) red and green incandescent modules and 40 percent of its yellow modules have been converted to LEDs, with numerous jurisdictions reporting 100-percent conversion. Due to the energy-saving benefits of LEDs, the California Energy Commission offered loans and grants to local agencies to assist them in their conversions. Elsewhere, the Kentucky Transportation Cabinet, through a contract program, converted the State highway system to LEDs in 6 months. On the national front, the switch to LED got a big boost recently from the Energy Policy Act of 2005, which requires that signal modules manufactured or imported after January 1, 2006, must meet or exceed specific energy efficiency requirements that currently can be met only by LED-type signals.
Another potential measure for increasing signal conspicuousness is a signal head setup called the "Red T Display," used most extensively in California. The display consists of the conventional red-yellow-green signal head but displays two red balls rather than just one at the top of the head. California uses this setup at intersections with high-speed approaches into a community. Winston-Salem, NC, studied the technique at 12 intersections and reports a 35-percent reduction in right- angle crashes.
Backplates. Signal backplates (thin strip of material on all sides of a signal housing) are commonly used by many States to provide a background for improved visibility of the signal indications, especially at locations where the lights are viewed against a bright sky or confusing background. The older drivers handbook cites studies showing that backplates can increase the intensity of the signal face by 33 percent. However, backplates increase wind loading on signal suspension systems. Therefore, as a general strategy, backplates are easier to apply to wind-resistant suspension systems, such as the mast arm system. At least eight DOTs (Alaska, Arizona, California, Iowa, Minnesota, Nevada, North Dakota, and Oregon) that use mast arms say that their States always use backplates on their signal heads. Kentucky is one of several States that supports some of its signal heads with span wire and uses backplates more selectively, such as at isolated rural locations.
To further increase the conspicuousness of traffic signals using backplates, FHWA has issued an interim approval memorandum for use of a 2.5-centimeter to 7.6-centimeter (1-inch to 3-inch) yellow retroreflective strip around the perimeter of the backplate face. According to Project 216 of the National Committee on Uniform Traffic Control of Canada, research in British Columbia indicates that the backplate borders are effective in reducing total signalized intersection-related crashes by up to 24 percent. Backplate borders also enable drivers to more readily locate the signal face and detect the presence of a signalized intersection during nighttime power outages. Illinois, Nebraska, and Ohio plan to start implementing this practice statewide, while Kentucky has initiated a pilot test using backplate borders at 10 intersections, and six other States and several cities also are trying the backplate borders at some intersections.
The growth rate of the older population and older drivers in particular will increase significantly as the baby-boom generation reaches retirement age. As noted in SAFETEA-LU, transportation professionals in all States should strive to improve traffic signs, signals, and pavement markings for older drivers and pedestrians. Many States are improving the driving environment for older motorists by enhancing delivery of roadway information and visibility of roadway delineation devices. Taking into consideration the needs of the older driver will benefit all users.
Because the State DOTs do not control and maintain the roads in most counties and municipalities, the older driver focus needs to extend beyond the State level if it is to be truly beneficial. Florida achieved its sign and marking changes nearly 15 years ago, but more changes are needed on local roads, under county and city jurisdictions, according to FDOT's Holley.
"The goal is to have a seamless road system," Holley says. Toward that end, she and colleagues have found it helpful to cite facts and figures "from the Purple Book," as she calls the older drivers handbook — a nickname that is gaining popularity based on the color of the cover. When provided with research statistics, local officials often are more receptive to making changes to their roadway signs and markings, says Holley.
Iowa DOT's Welch agrees, "An important secondary benefit of our enhanced signing program is that some city and county engineers are also improving their signing due to the comments they have received from residents who have seen the new signing on our State primary highways."
Felix E. "Gene" Amparano is a safety engineer on the Safety and Highway Design Technical Service Team at the FHWA Resource Center. He is the coordinator of the FHWA-sponsored Older Driver Highway Design Workshop and serves as an instructor. Before joining the Resource Center in 2001, he was an area engineer in FHWA's New Jersey Division Office. He holds a bachelor's degree in construction engineering from Missouri Western State College and a master's degree in civil engineering from Drexel University.
David A. Morena is the safety and traffic operations engineer at the FHWA Michigan Division Office. Morena developed the engineering agenda for the 2004 North American Conference on Elderly Mobility.
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