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SECTION V--DESCRIPTION OF STRATEGIES
the application of increased fines through more frequent visible enforcement activities will
help change driver perception about the likelihood of being cited for violations. In addition to
the possibility of being cited a large fine, the driver needs to have the perception that the fine
will be large and the sanction will be upheld by the courts. Otherwise, the sanction will be
reduced to the inconvenience of the court visit.
Forty-five states currently impose increased penalties for speed violations in work zones, and
in some states those increased fines apply to all types of violations. Studies show that many
drivers continue to violate the work zone speed limits in spite of these increased fines. Using a
consistent approach to enforcing work zone traffic laws and adjudicating citations is a way to
curb this trend. This will require seeking the cooperation of the judiciary. It can be facilitated
by encouraging a partnership and making sure that judges understand the importance of this
strategy for saving lives. More information on this strategy, with respect to use in work zones,
is discussed in greater detail in NCHRP Report 500, Volume 17 (Work Zones) of this series.
Doubling the fines in school zones may be one of the ways to improve compliance of speed
limits in those areas. Signs may be posted around the school showing the message that
speeding fines will be doubled. Public information campaigns may also be conducted to
educate people about the penalty of speeding in school zones. Without proper enforcement,
long-term effects may not be seen. More frequent enforcement activity may change drivers'
perceptions and adherence to speed limits. Washington State enacted a state legislation in
1996 doubling the fines for speeding in school crosswalk and playground zones after a
survey showed that 50 percent of drivers were not complying with reduced school zone
limits and also speeds in excess of 50 mph were observed during the survey. One-half of the
amount collected through doubling the fines was used for improving school zone safety like
installation of signs, replacing existing school zone crossing signs with new fluorescent
yellow-green signage. Similar strategies can be applied in problem locations in residential
areas, hospitals and places with large elderly populations and numbers of pedestrians.
Objective D--Communicate Appropriate Speeds through
Use of Traffic Control Devices
Traffic control devices are the primary means through which drivers are made aware of
traffic laws. The most basic device is the speed limit sign, informing drivers of the maximum
allowable safe travel speed, under any conditions. Variable message signs (VMS) provide
more personalized, current information. Active speed warning signs display current travel
speeds to drivers, and are intended to deter drivers from speeding and make them aware of
the appropriate speed. In-pavement techniques can also be applied to the actual roadway to
encourage safer speeds. The placement, visibility, and maintenance of all traffic control devices
are important features in effectively communicating speed limits clearly. Poorly placed devices
can have a negative effect on safety, and increase the chances of speeding-related collisions.
Strategy D1--Improve Speed Limit Signage (T)
The placement, visibility, and maintenance of speed limit signs are important features in
effectively communicating speed limits clearly. A speed limit sign that has been misplaced,
has low visibility, or is not properly maintained can result in ineffective communication of
speed limits, which consequently can fail to encourage drivers to obey the speed limit. This can
in turn have a negative effect on safety, and increase the chances of speeding-related collisions.
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Location and frequency of speed limit signs are two key elements to properly communicating
the speed limit. Speed limit signs need to be consistently placed at the proper locations (for
example, following major intersections), which will reinforce a driver's expectation of when
to look for a speed limit sign. This is especially important if there is to be a change in the
speed limit from one section of the roadway to the next.
If a speed limit change occurs at a location where a driver may not be expecting one, then
adding speed reduction signs should be considered. Along extended stretches of roadway
where there are no changes in the speed limit, additional signing is still important as a
reminder to drivers and also to inform drivers that may have entered the roadway at a
minor intersection.
In Minnesota, "Reduced Speed Ahead" signs are used to give advance notice of reduced
speed limits when the reduction is 15 mph or more. In urban areas, where speed reductions
to 55 mph or less are required, speed reductions signs are to be erected on both sides of the
roadway. This is to be followed by supplemental speed limit signs mounted on both sides of
the roadways through the reduced speed zone. Supplemental speed limit signs, through all
reduced speed zones, should be placed at intervals approximately equal to 60 seconds of
travel time at the posted speed limit. Signs may need to be spaced closer in urban areas due
to the increased number of access points. Minnesota sets 10 miles as the maximum spacing
between speed limit signs in rural areas. In urban areas a speed limit sign should be placed
at each interchange for traffic entering the mainline (Minnesota DOT, 2004).
As with placement, the driver's ability to see the sign is highly important if the driver is
expected to obey the speed limit. Two factors that may affect the visibility include the
mounting details (i.e., Is the sign properly mounted so that it is in a driver's field of vision?)
and letter/border size (i.e., Was the appropriate letter and border size chosen for the speed
limit such that a driver can easily read the sign?). For more information regarding the proper
mounting and sizing of speed limit signs, refer to the current MUTCD.
Often overlooked, the context of the environment around a sign can impact its visibility. In
urban areas where traffic signs and commercial signs may be abundant, a driver may need
additional assistance with locating the speed limit signs. This assistance may take on
different forms, but possibilities include using larger signs and removing or relocating
unnecessary signs.
The issue of maintenance is an important factor in a sign's visibility. Poor maintenance can
result in reduced visibility through many forms, including tree and shrub growth, vandalism,
and reduction of the sign's retro reflectivity. See Exhibit V-12 for more information about
improving speed limit signage.
Strategy D2--Implement Active Speed Warning Signs (Including Truck
Rollover Warnings) at High Risk Locations Where Excessive Speeds
and Potential Conflicts Are Expected (T)
Active speed warning signs, also known as radar speed displays, speed display signs or
speed trailers, are similar to variable message signs (VMS), except they have radar
technology that determines the traveling speed of vehicles. Active speed warning signs are
intended to deter drivers from speeding and improve awareness that they need to obey the
posted speed limit. Travel speeds are detected and then displayed on the message board.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-12
Strategy Attributes for Improving Speed Limit Signage (T)
Attribute Description
Technical Attributes
Target This strategy is targeted at providing improved signing to communicate speed limits
clearly and effectively, especially to drivers that are unknowingly speeding. The
proper sign type, location, and routine inspection and maintenance of signs can
deter speeding and facilitate enforcement by effectively communicating the proper
speed limit to drivers. All agencies can implement this strategy. This strategy may be
especially important where there is a higher percentage of older drivers, or the
visibility of signs is often obscured by adverse weather, such as drifting snow.
Expected Effectiveness There is a lack of studies evaluating the effect of proper signage and routine
maintenance on preventing speeding; however, the general principle is that there is
a higher likelihood that speed limits may be exceeded if drivers are unaware of the
actual speed limit. Furthermore, clear and unambiguous communication of the speed
limit to drivers is an important role of effective enforcement and prosecution of
speeders, especially if law enforcement and the courts are to view speeding as a
significant and preventable safety risk.
Keys to Success The consistent and correct placement of speed limit signs is the first step towards
effective communication. Further, selecting the proper design standards (i.e.,
lettering size) for the roadway is a fundamental requirement. Following deployment,
the upkeep of speed limit signs is necessary, especially if minimum retro reflectivity
levels are adopted by the highway agency. A GIS-based road sign inventory with
links to maintenance records is one possible tool that can be used to track and
manage sign maintenance activities and needs.
Another key to the success of speed limit sign improvements is that the posted
speed limit is reflecting an appropriate speed limit for the roadway. See Strategy A1
for setting appropriate speed limits.
Potential Difficulties The biggest difficulties associated with this strategy are maintaining a sign inventory
and routine inspection and maintenance of signs. This is especially difficult in urban
areas where there are many signs on the roads. Likewise, this can be a difficult task
for rural areas, where highway mileage with associated signage is high. Lack of
personnel to take inventory and provide maintenance and repairs to correct signs
can also be a potential difficulty for agencies that are understaffed for such duties.
Appropriate Measures Key process measures include the number of locations where poor signage was
and Data replaced, and the related effect it had on speeding vehicles. Additional data might
include identifying locations with improved signage and using this to compare to
locations with undesirable signage. Observing any negative effects that the adverse
signs have on safety and speeding may provide beneficial results in identifying the
effects of improved signage on speeding.
Associated Needs None identified.
Organizational and Institutional Attributes
Organizational, Highway agencies should review any policy concerning signage requirements to
Institutional and Policy ensure that they meet the current MUTCD guidelines. Agreement among neighboring
Issues jurisdictions as to the policy, sign requirements (placement, letter height, etc.),
routine inspection, and maintenance should be coordinated to ensure uniformity.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-12 (Continued)
Strategy Attributes for Improving Speed Limit Signage (T)
Attribute Description
Issues Affecting Implementation time for this strategy is short to moderate. Taking inventory of speed
Implementation Time limit signage can be time-consuming, depending on the size of the municipality or
jurisdiction. Once the inventory is taken, routine inspection should be geared to
those signs identified as priority for improvements.
Costs Involved This strategy should have a low implementation cost. Costs with this strategy include
personnel to take inventory, inspect, and provide maintenance to signs. Other costs
include the acquisition and installation of new signs. Development of a sign inventory
system would increase costs.
Training and Other Additional personnel might be needed for jurisdictions where there is not adequate
Personnel Needs staffing to take on duties related to sign design, erection, and maintenance. Staff
should also be properly trained to ensure consistent and effective signing practices.
Legislative Needs None identified.
Other Key Attributes
Compatibility of This strategy is compatible with and oftentimes necessary for enforcement,
Different Strategies education, and engineering strategies to be effective. Effective speed limit signing is
an important issue when informing drivers of reduced speed zones (Strategy E2).
Other Key Attributes to None identified.
a Particular Strategy
Depending on the type of speed sign, some are capable of displaying additional text, such as
"Slow," or they completely blank out when vehicles are driving at excessive speeds. This
blank-out feature is intended to discourage drivers from speeding excessively to test the
capabilities of the sign or their own driving audacity.
Active speed warning signs are similar to variable message boards and photo radar devices.
They are different from automated speed enforcement devices in that they do not take photos
and are not used for enforcement purposes. These signs differ from variable message boards
as they have the radar technology to detect actual vehicle speeds. Speed warning signs can
be used permanently at a location, or mounted on trailers and moved to different locations
for temporary use.
Speed warning signs can be used permanently at a location, or mounted on trailers and
moved to different locations for temporary use. One type of permanently mounted sign,
used by King County in Washington, features a 12-inch high fluorescent yellow-green
readout and is the same overall size and style as the existing speed limit sign. They are
placed directly below the existing speed limit sign on the same post. These signs are ideal
for neighborhoods as they are relatively small and do not stand out visually as much as a
portable trailer would.
A study of the effectiveness of speed warning signs on speeding (for a roadway with a 25 mph
posted speed limit) was reported by TranSafety, Inc., in May 1998, in the publication, Road
Injury Prevention and Litigation Journal. Conclusions from this report are based on the study,
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SECTION V--DESCRIPTION OF STRATEGIES
A Comparative Study of the Speed Reduction Effects of Photo-Radar and Speed Display Boards
(Bloch, 1998). The use of a speed warning sign reduced the mean speed by 5.8 mph at the
experimental site but had little effect 0.2 miles downstream (a 2.9 mph reduction in mean
speeds). A speed warning sign used in conjunction with intermittent enforcement resulted in
a 6.1 mph mean speed reduction at the experimental site and a 5.9 mph reduction in the
mean speed downstream of the display.
The study found that speed warning signs were the major contributing factor in reducing
the number of vehicles traveling at "excessive" speeds (i.e., at least 10 mph above the posted
speed limit) by 34.9 percent (Bloch, 1998). The study also found that when used in conjunction
with intermittent enforcement, speed display boards reduced the number of vehicles at
"excessive" speeds by 31.8 percent (Bloch, 1998).
Speed display signs can be used as a deterrent to speeding, which may result in decreased
speed-related crashes. Studies have found that these signs effectively contribute to decreased
travel speeds while in place, with mixed long-term results. In combination with enforcement
and other technology such as photo radar devices, speed display signs could have a greater
potential to reduce speeding.
The technology for detecting vehicle speeds and providing a real-time warning to drivers
can be applied to locations where there is a potential for heavy vehicle rollovers, such as a
sharp curve. In addition to speed, warning systems may need to collect other information
such as vehicle height and weight to determine the potential of a rollover crash. For
information specific to the issue of speed warning signs as part of an interactive truck
rollover warning system, refer to Strategy 12.1 E2 in NCHRP Report 500, Volume 13: "A
Guide for Reducing Collisions Involving Heavy Trucks."
As in other community-wide solutions, such as traffic calming, highway and/or
enforcement agency staff should host a neighborhood meeting to discuss the existing
condition with interested parties and identify possible solutions. If active speed warning
signs are the preferred mitigation method, an on-site investigation should be conducted to
determine a physical range along the roadway where the signs would best meet the needs of
the traveling public. See Exhibit V-13 for further discussion.
EXHIBIT V-13
Strategy Attributes for Implementing Active Speed Warning Signs at High Risk Locations Where Excessive Speeds
and Potential Conflicts are Expected (T)
Attribute Description
Technical Attributes
Target The target of this strategy is drivers who are willing to change their behavior when
given information on their actual travel speeds, and has the added advantage of
letting drivers know their speed is being monitored. Speed warning signs can be
used in locations where speeding has been observed or may pose a safety risk (i.e.,
prior to a sharp horizontal curve, school zone, roadway section with a lower speed
limit, and any location with a history of speed-related crashes). This strategy can also
be used in cooperation with law enforcement efforts or as a substitute for enforcement
at locations that cannot be adequately patrolled due to a lack of personnel.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-13 (Continued)
Strategy Attributes for Implementing Active Speed Warning Signs at High Risk Locations Where Excessive Speeds
and Potential Conflicts are Expected (T)
Attribute Description
Expected Effectiveness Studies on speed warning signs have found the technology to be effective at
reducing vehicle speeds while the signs are in place, especially for vehicles that are
10 mph or more above the posted speed limit (see discussion in the strategy
introduction). Significant speed reductions were not sustained after the devices were
removed. However, it was noted that one long-term, statistically significant effect
occurred with the unenforced speed display board: a 1.7-mph decrease in speed
continued at an experimental site after the display board was removed.
Meyer (2000) noted that changeable message signs are unlikely to be able to reduce
speeds by 10 mph or more in A Literature Review of Perceptual Countermeasures to
Speeding.
Keys to Success A key to the success of this strategy is identifying the locations that will have the
greatest benefit from active speed warning signs (whether permanent or temporary).
Locations should have a history of speeding and/or speed-related collisions.
Observations from concerned citizens and law enforcement officials are often good
sources for this information. Selected locations will likely have the greatest potential
for success if both highway agencies and law enforcement agencies are involved in
the process of determining locations to deploy the signs.
Another important key to success is educating the public on the need for and
benefits from speed warning signs in order to gain their acceptance. Likewise, it is
important for local agencies, such as law enforcement and highway agencies to
initially accept the need for speed warning signs.
Potential Difficulties The public may initially be resistant to speed display signs, especially those
accompanied with photo-radar or traditional enforcement. Because of the possibility
for negative opinion, public outreach is needed early in the process so that the public
understands the reasons for using the signs. It is especially important to inform
drivers of where speed display signs are used in conjunction with enforcement.
Appropriate Measures A key process measure is the number of road segments where active speed warning
and Data signs are installed. A more detailed measure includes observing any changes in the
number of speeding vehicles and in the speed profiles. When used in conjunction
with photo-radar enforcement, data concerning the number of citations issued should
be collected.
Changes in the crash history and severity of speed-related collisions are good
indicators of safety effectiveness. Data on speed-related crashes at locations of the
speed displays should be collected before and after the installation of the signs. It is
also important to monitor the long-term performance of the speed display sign to
ensure that it remains effective.
Associated Needs Informing the public on the use of speed displays is important. Informational
materials should include:
· Local issues with speeding
· Safety advantages to using active speed warning signs
· General locations where active speed warning signs are used
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EXHIBIT V-13 (Continued)
Strategy Attributes for Implementing Active Speed Warning Signs at High Risk Locations Where Excessive Speeds
and Potential Conflicts are Expected (T)
Attribute Description
· Whether speed warning signs are used in conjunction with photo-radar or
traditional enforcement (if so, use of revenue from automated enforcement)
Conveying this information to the public may help extend the period of effectiveness
of the signs.
Organizational and Institutional Attributes
Organizational, Highway and law enforcement agencies need to develop or review policy regarding
Institutional and Policy the deployment of speed display signs, especially how the agencies will respond to a
Issues neighborhood's request to address a speed problem (perceived or actual). In the
situation where the request is being made by the public, policies should also address
which type of display will be used (permanent or temporary), how long temporary
displays will be used at the location, and what actions an agency may take if the sign
displays prove not to be effective at a particular location.
Agencies should also consider developing guidelines and criteria to help in the
identification of locations where speed display signs (with or without enforcement)
would be warranted.
Issues Affecting Implementation time for active speed warning signs can typically be performed in
Implementation Time less than 1 year (especially for portable signs), but can vary depending on the level
of public involvement, acquisition of signs, and additional personnel or studies
needed.
Costs Involved Costs will vary, but are expected to be low. The main costs are those which include
data collection for prioritizing locations, acquisition, installation (does not apply to
portable signs which can be placed in locations temporarily via truck and trailer), and
maintenance. The acquisition and installation cost of permanent active speed
warning signs is much higher compared to mobile ones.
Training and Other No significant training or increases in personnel should be needed for the
Personnel Needs installation, operation and maintenance of a speed warning sign.
Legislative Needs Local legislation might cover requirements that address local needs for active speed
warning signs such as operating criteria, agency responsible for operation and
maintenance of signs, and restrictive uses (such as using in conjunction with photo-
radar enforcement).
Other Key Attributes
Compatibility of This strategy is compatible with the others discussed in this guide. This strategy
Different Strategies relies on the similar technology discussed in Strategy C2 (automated speed
enforcement); therefore, these two strategies can be used in conjunction.
Other Key Attributes to None identified.
a Particular Strategy
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Strategy D3--Use In-Pavement Measures to Communicate the Need
to Reduce Speeds (T)
This strategy relies on the use of perceptual and in-pavement techniques to encourage drivers
to proceed at a safe travel speed. This strategy can be applied along a roadway segment as well
as at locations such as intersection approaches, work zones, toll plazas, ramps, and so on.
Perceptual Pavement Markings
Perceptual pavement markings give the driver the illusion of traveling faster than his or her
actual speed in order to decrease the driver's comfort at excessive speeds. At locations where
drivers are expected to reduce their speed, such as the beginning of a school zone, approach
to an intersection, entrance to a residential neighborhood, or prior to a sharp horizontal
curve, a converging pattern of pavement markings can be used to give the perception to the
drivers that they are increasing their speed if they fail to slow down at a sufficient rate.
Pavement markings can also be used for other perceptual applications, such as to give the
illusion of lane narrowing. This method is intended to reduce a driver's comfort at an
excessive speed while proceeding through the markings, as a way to encourage deceleration.
This type of treatment has potential applications along the entire length of a corridor.
Perceptual pavement markings are good candidates for roads where speeding is known to
play a role in either crash frequency or severity. Furthermore, perceptual techniques are
expected to reduce travel speeds without the need for increased enforcement, and should be
able to affect driver behavior regardless of whether a driver is intentionally or unintentionally
speeding. Perceptual pavement markings can also encourage drivers to decelerate at an
appropriate rate on the approach to an area with a reduced speed limit (i.e., school or work
zone or intersection).
Perceptual pavement markings have several
advantages over traditional speeding
countermeasures. First, the cost of applying
perceptual pavement markings is very low;
however, the pavement markings must be routinely
maintained in order to prevent a decrease in their
visibility. Second, perceptual techniques are also
very flexible since they can be used to target
speeding specifically in high-risk areas, or for the
whole length of a corridor. Finally, this strategy can
be used for areas where law enforcement is not
readily available, or can be used in conjunction with
law enforcement for increased speed reductions.
There are several different types of perceptual
techniques. The following are examples of different
perceptual pavement techniques that have been in use.
· Transverse Lines: Transverse pavement mark-
ings are dashed lines that span the width of a
travel lane. These pavement markings can be
used to create the illusion that lane widths are Source: Katz, 2004
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decreasing or narrowing, an effect that is perceived when the driver is traveling at higher
speeds. A study in Kansas found that using these pavement markings at work zones
decreased speeds and reduced the variation in speeds, though the speed reductions were
fairly small (Meyer, 2001).
· Peripheral Transverse Lines: Peripheral transverse lines are the same as the transverse
lines discussed above but they are used at the edges of travel lanes rather than across the
entire lane. A study, as cited in Katz's report Pavement Markings for Speed Reduction,
found that peripheral transverse lines performed the same, and in some occasions better
than, full-length transverse lines. Full-length transverse lines tend to decrease vehicle
speeds upon entering the zone with transverse lines; however, vehicle speeds tend to rise
again after time.
· Converging Chevrons: Chevrons can also be used in a
converging pattern. This pattern is characterized by a
series of chevrons on the pavement surface that are
placed progressively closer together. The first chevrons
encountered by a driver passing through the pattern are
widely spaced; those later in the pattern are closer
together. The intent of this pattern is to create the illusion
that drivers are traveling faster than they really are and
to foster the impression that the traffic lanes are narrow-
ing. These are sometimes accompanied by a dashed
edge line. This edge line may promote the perception in
drivers that the traffic lane is narrower than it really is.
This perception can encourage a driver to reduce his/her
speed (Griffin and Reinhardt, 1995). Source: Katz, 2004
Speed reduction can be further enhanced when these perceptual pavement techniques are
combined with other in-pavement measures like rumble strips--discussed later in this
strategy.
The Manual on Uniform Traffic Control Devices (2003) provides guidelines on the use of
pavement markings as well as details concerning standard colors, dimensions, and
placement.
Additional information can be found on the use of perceptual pavement markings in the
discussion for Strategy 15.1 A4 in NCHRP Report 500, Volume 6: "A Guide for Addressing
Run-Off-Road Collisions."
Rumble Strips
In addition to perceptual pavement marking techniques, in-pavement strategies, such as
rumble strips, can be deployed as a means to reduce vehicle speeds and/or prevent crash
types where speeding may play a significant role, like a lane departure crash, or a transition
from a high-speed zone to a low-speed zone. Rumble strips can also be used as a traffic
calming tool in high pedestrian areas, such as neighborhoods and school zones.
Rumble strips are grooves installed in the road surface intended to draw drivers' attention to
the roadway environment--either that the vehicle is drifting out of the travel lane, or that
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SECTION V--DESCRIPTION OF STRATEGIES
there is a situation ahead that requires more attention or deceleration. When a vehicle travels
over a rumble strip, the driver is warned through the vehicle vibrations and the noise it
produces.
There are three types of rumble strip applications.
· Continuous Shoulder Rumble Strips: This is the most common type of rumble strip that
is typically applied to the shoulder of high-speed roads. These aim to prevent run-off-
road accidents. The primary use of this type of rumble strip for speeding-related crashes
is not to reduce vehicle speeds, but is instead to provide an additional warning to drivers
leaving the roadway, especially those that are speeding.
· Centerline Rumble Strips: These are applied to the centerline of high-speed roads.
Centerline rumble strips aim to prevent median crossing or head-on collisions. Again,
this application's primary intent is not to reduce speeding (although they may provide
the illusion of lane narrowing, which may slow drivers), but is instead to warn drivers
they are crossing the centerline.
· Transverse Rumble Strips: These are used at intersection approaches, toll plazas, work
zones, ramps, and extreme curves. The warning provided by the transverse rumble
strips should help drivers recognize that they need to slow down, possibly even come to
a complete stop depending on the situation.
For more information, see FHWA Research and Technology's Priorities, Market-Ready
Technologies and Innovations, Rumble Strips at http://www.fhwa.dot.gov/rnt4u/ti/
rumblestrips.htm.
Rumble strips are commonly applied on the side of rural roads to deter vehicles from
leaving the traveled way, and are increasingly used at the centerline of high speed roads.
On low speed roadways, transverse rumble strips are used to alert drivers of a speed zone
transition. On a state highway, speed reduction will typically occur in a transition from rural
to downtown conditions. Transverse rumble strips can be used on approaches to a main
street where a speed reduction is desired and where speed limit or warning signs are already
in place. They are used to target drivers that are inattentive, drowsy/fatigued, careless, or
distracted (FHWA Research and Technology). Rumble strips are also safety measures during
adverse weather conditions. Fog, snow, rain and related weather events can reduce the
visibility of pavement markings and road signs (FHWA Research and Technology). Rumble
strips have the advantage in these types of conditions of not relying on visibility to be effective;
however, some states paint rumble strips to increase their visibility during favorable conditions
(FHWA Research and Technology).
Intersections, work and school zones, neighborhoods, toll plazas, and freeway ramps are
all locations that are vulnerable to speeding-related collisions and pose risks to drivers,
workers, or pedestrians. Rumble strips are low-cost measures that can be taken to prevent
collisions at these locations, by providing warning and increasing awareness of changes in
the road environment to drivers.
NCHRP Report 500, Volume 6: "A Guide for Addressing Run-Off-Road Collisions" provides
supplemental information on the application of shoulder rumble strips to decrease run-off-
road collisions, while NCHRP Report 500, Volume 4: "A Guide for Addressing Head-On
Collisions" provides a review of centerline rumble strips to prevent head-on crashes. Both
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SECTION V--DESCRIPTION OF STRATEGIES
of these strategies are again reviewed in NCHRP Report 500, Volume 7: "A Guide for
Reducing Collisions on Horizontal Curves." The use of transverse rumble strips was also
reviewed in depth in NCHRP Report 500, Volume 5: "A Guide for Addressing Unsignalized
Intersection Collisions." For additional information on the application and issues for rumble
strips, refer to the mentioned guides.
Traffic operation personnel should consider rumble strips that are compatible with motorcycle
and bicycle use. An abrupt rise in the roadway can present problems to bicyclists and
motorcyclists. For this reason, there should be provisions made for cyclists to safely traverse
through or around raised rumble strips. See Exhibit V-14 for more detail on this issue.
EXHIBIT V-14
Strategy Attributes for Using In-Pavement Measures to Communicate the Need to Reduce Speeds (T)
Attribute Description
Technical Attributes
Target The perceptual pavement markings and transverse rumble strips are intended to
give drivers a warning when entering a high-risk area at a potentially unsafe speed.
Perceptual pavement markings can help a driver select a safe speed while
transverse rumble strips are a warning that the driver is approaching a situation that
requires more attention.
Shoulder and centerline rumble strips are not intended as a speed reduction strategy,
but instead will provide drivers with a warning when crossing the centerline or leaving
the roadway, which are crash types in which speeding may play an important role.
These strategies can be deployed on the approach to high-risk areas, such as
sharp horizontal curves, intersections, school zones, work zones, neighborhoods,
speed zone transitions and toll plazas, or can be deployed continuously along a
high-speed corridor (such as freeway facilities and arterial highways).
Expected Effectiveness It is expected that perceptual pavement marking techniques can reduce speeding
and have the potential to reduce collisions. There are several studies on the
effectiveness of perceptual pavement techniques that indicate successful
applications in reducing vehicle speeds.
Katz (2004a) reviewed the effects of perceptual techniques in the study, "Perceptual
Pavement Marking Techniques as a Low-Cost Safety Improvement to Reducing
Vehicle Speeds" at the 2004 Annual Meeting and Exhibit of the Institute of
Transportation Engineers. His study indicated that perceptual techniques can provide
results beneficial to safety and can also reduce speeding. Results from a study in
Kansas indicated that optical speed bars cause reductions in mean speed, 85th
percentile speed and speed variation (Meyer, 2001). A different study indicated that
perceptual markings effectively decreased travel speeds where there was a high
frequency crash history at a sharp curve in Kentucky (Agent, 1980). A study in
Wisconsin found that chevron pavement markings that were placed at the exit ramp
of a freeway reduced travel speeds by up to 17 mph after 20 months of installation
(Drakopoulos & Vergou, 2003). However, the perceptual pavement markings
have not always demonstrated the ability to reduce speeds over the long term.
Furthermore, questions have been raised if the decrease in travel speeds was due to
the speed illusion or simply because the drivers recognized the presence of pavement
markings as a warning of a hazardous location (NCHRP Report 500, Volume 6 ).
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-14 (Continued)
Strategy Attributes for Using In-Pavement Measures to Communicate the Need to Reduce Speeds (T)
Attribute Description
Perceptual techniques such as widening centerline markings (to provide the illusion
of a narrower travel lane) and their effects have been studied in Europe. A study in
the Netherlands found that applications along roads with posted speed limits of
80 kph (50 mph) produced speed reductions of 5 to 10 kph (3 to 6 mph). During this
study a 36 percent reduction in crashes was observed for the roads where the
application was used on a trial basis, while the control roads experienced an
increase in crashes of 17 percent (FHWA, 1995). It can be expected that these
speed reductions can be somewhat less on lower speed roads, depending on the
severity of the speeding problem.
Also, it should be considered that various pavement marking patterns may show
relatively little effect on vehicle speeds but still serve to reduce the probability of
traffic crashes. This is to say, even if perceptual pavement marking patterns do not
dramatically reduce vehicle speeds, they may alert or rouse the driver into a
heightened sense of awareness in which they are better prepared to avoid a crash
(Griffin and Reinhardt, 1995).
There are numerous studies that indicate the beneficial safety effects of the
application of rumble strips in reducing run-off-road and head-on crashes. The
FHWA has sponsored several studies that indicate rumble strips can reduce run-off-
road collision by 20 to 50 percent (NCHRP Report 500, Volume 6). While there are
many studies that indicate the safety benefits of shoulder rumble strips, there are
also benefits to the application of transverse rumble strips.
Portable rumble strips in rural work zones were found to have a positive impact on
safety. Results from this study found that the average travel speed of passenger
vehicles was reduced by 2 mph and the number of cars exceeding the speed limit
decreased by up to 7 percent (Fontaine and Carlson, 2001). The same study found
that rumble strips had a bigger impact on reducing average speeds of trucks, by up
to 7 mph (Fontaine and Carlson, 2001).
The Minnesota DOT reports that rumble strips have been used in work zones since
the 1950's (Corkle, Marti, and Montebello, 2001). The study indicates that rumble
strips in construction zones are typically used in conjunction with warning signs,
flagging, and barricades. These devices likely add to the effectiveness of rumble strips.
Keys to Success A key to the success of this strategy is identifying and prioritizing locations that can
benefit from perceptual pavement markings, rumble strips or other in-pavement
strategies. Identification of roadways for this application includes those where
enforcement is not available, speeding is a problem at high speed limits, and there
is a history of speed-related collisions.
Provided that the use of transverse rumble strips is as effective as studies indicate,
states should install them at locations as suggested. Further proof of effectiveness,
through observing nationwide studies, is important prior to future installation of
transverse rumble strips at intersections, school and work zones, neighborhoods,
ramps, and toll plaza locations.
A key to success for installation of transverse rumble strips is identifying locations
where they would be most effective. In order to identify and prioritize these locations,
it is important to look at crash history and severity, as well as travel speeds.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-14 (Continued)
Strategy Attributes for Using In-Pavement Measures to Communicate the Need to Reduce Speeds (T)
Attribute Description
Another key to success for the implementation of transverse rumble strips is using
them properly and in conjunction with other safety measures. For example, rumble
strips can be more effective when used with proper flagging and signage in work
zones.
Potential Difficulties The biggest issue for perceptual pavement markings is identifying locations where
perceptual pavement techniques should be applied. Also, careful consideration
needs to be given to the design of the pavement markings, especially converging
patterns, in order to produce the desired effect and be consistent with requirements
and guidelines in the MUTCD.
Incompatibilities and issues may exist between rumble strips and certain motor
bikes and bicycles. It is possible for cyclists to lose control while traveling over
rumble strips (e.g. wheel catching in rumble strip). It is recommended by the FHWA
in Technical Advisory on Roadway Shoulder Rumble Strips that they not be used in
locations where there are bicycle paths or a high number of cyclists (FHWA, 2001).
This is an issue since the transportation community encourages the use of bicycles.
This strategy, therefore, targets toll plazas and freeway ramps, which are locations
where bicycling is prohibited.
Another possible issue with rumble strips is that they can produce additional risk. It
has been found that it is common for drivers to merge into opposing lanes or swerve
abruptly to avoid the rumble strips. This poses alarming risks to safety by providing
exposure to head-on collisions or severely injuring workers at toll plazas or in work
zones, or putting pedestrians and bicyclists at risk in downtown and residential areas.
There are issues regarding adverse weather and rumble strips. Rumble strips can
be ineffective when ice or snow builds up in them. Likewise, snow removal is
difficult with conventional plows as they cannot pick up snow packed in the grooves
of rumble strips.
Rumble strips also can be a noise nuisance when placed in close proximity to
residential areas. This may not be a well accepted alternative by residents. Public
involvement must take place before rumble trips are installed in a residential area.
Appropriate Measures One key process measure is the number of corridors and locations where
and Data perceptual pavement markings and other in-pavement countermeasures have been
applied. Identifying average travel speeds and crash history before and after the
installation of the countermeasure can be used to determine the overall effect.
Road characteristics should be noted, to indicate areas where this strategy might be
more useful or at locations where it is not as successful, for the use of future
applications. Other appropriate measures include gathering information and
feedback from the public. For example, it is important to listen to concerns from the
public on issues with rumble strips such as noise or use with bicycles.
Associated Needs Information campaigns may be needed to inform the public of the purpose of the
markings prior to the installation of pavement markings.
As identified in NCHRP Report 500, Volume 6, there have been reports of persons
mistaking the noise produced from rumble strips as car problems. Public information
and educational campaigns can be used to reduce these misinterpretations.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-14 (Continued)
Strategy Attributes for Using In-Pavement Measures to Communicate the Need to Reduce Speeds (T)
Attribute Description
Organizational and Institutional Attributes
Organizational, Highway agencies should have a design policy for perceptual pavement markings
Institutional and and other in-pavement countermeasures that can be used for speed zone transitions,
Policy Issues neighborhoods, work and school zones, freeway ramps, toll plazas, and intersections.
If highway agencies do not have a policy concerning these countermeasures, then
these need to be developed first before the strategy is implemented.
Many states have specific design and placement criteria concerning conventional
rumble strip applications (shoulder rumble strips). Policy for transverse rumble strips
should be implemented with design and placement criteria for speed zone transitions,
neighborhoods, work and school zones, freeway ramps, toll plazas, and intersections.
Issues Affecting Implementation time for this strategy is expected to be low. The process of
Implementation identifying and prioritizing locations may lengthen implementation time.
Time
Costs Involved Costs for perceptual pavement markings will vary depending on the length of
corridor to which the markings will be applied. The overall cost of perceptual
pavement techniques is rather low compared to other speed reducing techniques,
as pavement markings are inexpensive to install and maintain.
Due to advances in construction technology and increased applications of rumble
strips, the cost of installation has been on the decline. NCHRP Report 500, Volume 6
reported that the New York Department of Transportation paid approximately
$6.18 per linear meter of rumble strip in 1990. This decreased to only $0.49 per
linear meter in 1998. The costs associated for transverse rumble strips, as described
for applications in this strategy, would be much lower because ramps, toll plazas,
work zones, and intersections do not require continual rumble strips at extensive
lengths. Costs for maintenance of rumble strips are generally minimal.
Training and Other No additional training or personnel should be needed for this strategy.
Personnel Needs
Legislative Needs None identified.
Other Key Attributes
Compatibility of Use of enforcement with these countermeasures may help increase their effectiveness
Different Strategies at reducing speeding and speeding-related crashes. Also, perceptual pavement
markings can be used to help control speeds on approaches to reduced speed
zones (Strategy E2) and can also be combined with geometric design elements to
control speeds (Strategy E1).
Other Key Attributes to None identified.
a Particular Strategy
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SECTION V--DESCRIPTION OF STRATEGIES
Strategy D4--Implement Variable Message Signs to Display Information on
Appropriate Speeds for Current Conditions, As Well As Technologies to Monitor
Conditions (High Speed Only) (T)
Variable message signs (VMS) are used to provide drivers information concerning the
current and expected driving conditions. VMS display messages to drivers that will inform
or warn them of conditions ahead that may prove beneficial to their safety or travel time.
Examples of information commonly displayed by VMS are:
· Traffic conditions
· Work zone/construction areas
· Weather and surface conditions
· Detour/direction information
· Crashes and incidents
· Appropriate speed limits
There are several different types of VMSs, such as flip disk, light emitting diode (LED),
and fiber optic displays (Wisconsin DOT, 2000). LED and fiber optic are two of the more
common technologies in use today for the display of messages. VMS can be either
permanent fixtures often mounted over the roadway or can be smaller, trailer mounted
displays which are placed on the roadside. Both forms have a limited space for long
messages with multiple text items; therefore, they are programmed to flash one item
after another. The messages displayed on some VMS can be programmed on-site or
remotely. This allows for a rapid update of information on current and expected travel
conditions.
VMS displays provide advanced technology to indicate safe travel speeds to drivers. For
certain conditions (i.e., congested roadways or inclement weather), the posted speed limit
may not be a safe travel speed; however, drivers will often attempt to drive at the posted
speed limit despite the safety problems this may create. A key element to this strategy's
effectiveness is the support from enforcement and adjudication when speed limits are
decreased due to conditions.
In addition to using ITS to display a safe speed for the driving conditions, ITS technology is
needed to collect information on current conditions so that speed limits can be accurately set.
Traffic conditions can be observed using video cameras and/or pavement loop detectors.
Video can also be used to observe weather conditions, along with weather stations.
Furthermore, in-pavement sensors are available for collecting information on actual
pavement conditions, including pavement surface condition and temperature. Often this
information can be gathered and then sent to a central location, such as a traffic management
center in a large metropolitan area, for processing and display on VMS. See Exhibit V-15 for
more information on how to use VMS.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-15
Strategy Attributes for Implementing Variable Message Signs to Display Information on Appropriate Speeds
for Current Conditions As Well As Technologies to Monitor Conditions (T)
Attribute Description
Technical Attributes
Target This strategy is targeted at reducing crashes related to traveling at speeds faster
than what is appropriate for current conditions. Real-time communication of current
conditions is provided to help drivers make better choices concerning their speed.
VMS technology is ideal for high-speed roads such as freeways and arterials that
have a history of speeding-related crashes (especially during congested conditions
or adverse weather).
Expected Effectiveness It is difficult to determine the effectiveness of this strategy in reducing crashes
related to speeds higher than appropriate for conditions, as there are a variety of
other factors that can affect the occurrence of crashes that are difficult to measure.
There are a few studies which quantify the actual effectiveness of VMS presence
and its ability to deter speeding. Studies indicate that VMS are effective in gaining
travelers' attention. One particular study indicates that drivers feel VMS is reliable
and provides them with helpful information while traveling (Ran et al., 2004).
A survey by the Wisconsin DOT was administered to determine if VMS displays are
effective ways to communicate information to travelers. Results from the survey
(sample of 200+ respondents) indicated that the majority of the drivers are familiar
with VMS, with 70 percent of the respondents indicating viewing VMS on their
routine routes (Ran et al., 2004). From the total respondents, the collective attitude
was positive, indicating that drivers feel the information displayed is reliable. They
indicated that VMS were particularly informative concerning weather and traffic
condition updates.
Keys to Success The Wisconsin DOT's Intelligent Transportation Systems Design Manual identifies
criteria that are useful for successful deployment of a VMS system (Wisconsin DOT,
2000). The manual indicates the following criteria for determining the use of VMS:
· Data Collection: Data collection to determine where VMS would be most
effective includes mapping of area, road alignment information, crash history, an
inventory of existing signs, locating power sources along the road (to provide
electricity to VMS).
· Determine Type of VMS: Determining the type of VMS depends on the intended
purpose for the signs. For displaying speed information it is important to consider
VMS technology that is capable of displaying several lines of information. Some
VMS signs are limited in the information that can be displayed. It is important to
obtain a sign that is capable of displaying several lines of information concerning
appropriate speed limits, traffic conditions, weather conditions and other related
items that would have an effect on safe traveling speeds.
· Identify Locations to Install VMS: Once data are reviewed, locations for VMS
should be identified. This should be based primarily on the need for the signs.
High-priority locations where VMS would be effective should be identified and
exact locations to install the signs should be determined.
Data collection is needed to know if a speed adjustment is warranted; this data is
equally important to the effective and efficient location of VMS. Without timely and
accurate data, drivers are more likely to disregard the suggested driving speeds.
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SECTION V--DESCRIPTION OF STRATEGIES
EXHIBIT V-15 (Continued)
Strategy Attributes for Implementing Variable Message Signs to Display Information on Appropriate Speeds
for Current Conditions As Well As Technologies to Monitor Conditions (T)
Attribute Description
Potential Difficulties Convincing drivers that they need to obey the suggested speeds could be one of
the biggest difficulties. As with any speed limit or speed advisory sign, drivers will
not necessary obey them, especially if the information is not up-to-date.
Another potential problem may be legibility of the messages. Also drivers should not
be overwhelmed with too much information which may cause distraction by taking
too much reading time and causing vehicles to slow down.
Another identified difficulty of this strategy is the costs associated with VMS. The
acquisition, installation, and routine maintenance of variable message displays and
the data collection equipment can be very costly.
Appropriate Measures As mentioned previously, data collection is important to determine effective
and Data locations to install VMS. Measures and data appropriate to determine the
effectiveness of VMS at those locations include obtaining historical and current data
concerning speeding at locations where VMS is installed. Crash data concerning
speeding and various conditions such as weather and congestion are also important
to identify, if available. These data items should be observed for current and future
conditions after the VMS is installed, to determine the effectiveness of VMS.
Associated Needs A public information campaign may be needed to inform drivers of the intent of
VMS, especially if use of them in this manner is new to an area. A survey or other
method of obtaining feedback from drivers can be a good way to gain information
on the use, location, and other issues related to the signs.
Technology to detect adverse conditions (high winds, snow, rain, fog, etc.)
contributes to success in providing updated information displayed on variable
message signs.
Organizational and Institutional Attributes
Organizational, Policy guidance regarding the installation of VMS should be considered with the
Institutional and MUTCD as a reference.
Policy Issues
Issues Affecting Implementation time can vary depending on the process to identify proper locations
Implementation Time and type of VMS to install. The data collection process is likely the longest task for
this strategy. Acquiring and installing the VMS should not take long, especially if
there is infrastructure to accommodate the signs (e.g., power supply or bridge to
hang sign).
In addition, the installation of data collection equipment can vary based on the size
of the network observed and the technology selected.
Costs Involved Costs for this strategy can be moderate to high, due to the detection and
communication equipment needed. There are several different costs associated
with this strategy. The major costs include the acquisition, installation, and routine
maintenance of the VMS and data collection equipment. The costs are much higher
if infrastructure to mount the signs (such as a bridge overpass) and a power supply
does not exist.
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