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controlled primarily by the thickness of the water film on the pavement surface, the design
guidelines focus on the prediction and control of ache depth of water flowing across the
pavement surface as a result of rainfall, often referred to as sheet flow.
Water film thickness on highway pavements can be controlled In three fundamental
ways, by:
I. Minimizing the length of the longest flow path of the water over We pavement and
thereby the distance over which the flow can develop;
2. Increasing the texture of the pavement surface; and
3. Removing water from the pavement's surface.
In the process of using PAVDRN to implement the design guidelines, the designer is
guided to (~) minimize the longest drainage path length of the section under design by altering
the pavement geometry and (2) reduce the resultant water film thickness that will develop
along that drainage path length by increasing the mean texture depth, choosing a surface that
maximizes texture, or using permeable pavements, grooving, and appurtenances to remove
water from the surface.
Through the course of a typical design project, four key areas need to be considered in
order to analyze and eventually reduce the potential for hydroplaning. These areas are:
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I. Environmental conditions:
2. Geometry of the roadway surface;
3. Pavement surface (texture) properties; and
4. Appurtenances.
Each of these areas and their influence on the resulting hydroplaning speed of the designed
section are discussed In detail In the guidelines (21.
The environmental conditions considered are rainfall ~ntensibr and water temperature,
which determines the kinematic viscosity of the water. The designer has no real control over
these environmental factors but needs to select appropriate values when analyzing the effect of
flow over the pavement surface and hydroplaning potential.
Five section types, one for each of the basic geometric configurations used In highway
design, are examined. These section are:
1. TaIlgent;
2. Superelevated curve;
3. Transition;
4. Vertical crest curve; and
5. Vertical sag curve.
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Pavement properties that affect the water fihn thickness mclude surface characteristics,
such as mean texture depth and grooving of Portland cement concrete surfaces, are considered
In the process of applying PAVDRN. Porous asphalt pavement surfaces can also reduce He
water film thickness and thereby contribute to the reduction of hydroplaning tendency and their
presence can also be accounted for when using PAVDRN. Finally, PAVDRN also allows the
design engineer to consider the effect of drainage appurtenances, such as slotted drain inlets.
A complete description of the various elements that are considered In the PAVDRN program is
illustrated In figure 40. A more complete description of the design process, the parameters
used in the design process, and typical values for the parameters is presented In the "Proposed
Design Guidelines for Improving Pavement Surface Drainage" (2) alla in Appendix A.
fIN1)INGS
The following findings are based on the research accomplished during the project, a
survey of the literature, and a state-of-the-art survey of current practice.
I. Model. The one~unensional mode} is adequate as a design tool. The simplicity
and stability of the one~imensional mode} offsets any increased accuracy afforded
by a two-d~mensional model. The one~mensional model as a predictor of water
fiDn thickness and How path length was verified by using data from a previous
study (11).
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No. of Planes
Length of Plane
Grade
Step Increment
Wdth of Plane
Cross Slope
Section T,rne
1) Tangent
2) Honzontal Curare
3) Transition
4) Vertical Crest
5) Vertical Sag
U=tS
1)U.S.
2) S. I.
Rainfall
Intenstity
~ , \
|Kinematic Viscosity
|Design Speed
Note:
PC = Point of Curvature
PI. = Point of Tangency
PCC = Portland cement
concrete
WAC = Dense graded
asphalt concrete
0GAC = 0pcn~raded
asphalt concrete
where OGAC
includes all types of
intentally draining
asphalt surfaces
GPCC = Grooved Ponland
cement concrete
Taneent
Pavement Type
Mean Texture Depth
1) PCC
2) DGAC
3) OGAC
4) GPCC
Horizontal Cun~c
Grade
Cross Slope
Radius of Cunran~re
Wdth
Pavement Type _ 2) DGAC
3) OGAC
4) GPCC
Mean Texture Depth
Step Increment
_
Transition
Length of Plane
Super Elevation
Tangent Cross Slope
Tangent Grade
width of Curve
Transition Width
Pavement Type_ 1) PCC
3) OGAC
4) GPCC
Mean Texture Depth
Step Increment
Horizontal Length
Cross slope
width
PC Grade
PI' Grade
Elevation: Pr-PC
Vertical Crest
Flow Direction
Step Increment
Pavement Type
1) PC Side I
2) PI. Side |
1)PCC
2) DGAC
3) OGAC
4) GPCC
Mean Tex~rc Depth
_ _ ~
Figure 40. Factors considered in PAVDRN program.
122
~1
r -
. ,
Vertical Sad |
Horizontal Length |
Cross slope
Wldth
PC Grade
PI Grade
Elevation: PIE
Flow Direction
Step Increment
/ Stored :_
~ cats ~
1) PC Side |
2) PI Side |
.
Pavement Typed 1) PCC
3) OGAC
14) GPCC
Mean Texture Depth I I
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~ Stored data V ~
3
L
IN1T
For use with a second
nut using data from the
first run.)
, 1
EPRINT
(Echos input to output )
1
CONVERT
(Converts units to and
from SI and English.)
~ ,
ADVP
(Advances Page of
output.)
KINW
(Calculates Minning's
n, Water Film
Thickness (WEIR), and
Hydroplaning Speed
UPS).)
,
EDGE
(Determines if flow has
reached the edge of the
pavement.)
out roar
Figure 40. Factors considered in PAVDRN program (continued).
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2. Occurrence of Hydropl~r g. In general, based on the PAVDRN mode! and the
assumptions inherent in its development, hydroplaning can be expected at speeds
below roadway design speeds if the length of the flow path exceeds two lane
widths.
3. Water Film Thickness. Hydroplaning is initiated primarily by the depth of the
water film thickness. Therefore, the primary design objective when controlling
hydroplaning must be to limit the depth of the water film.
4. Reducing Water Film Thickness. There are no simple means for controlling water
John thickness, but a number of methods can effectively reduce water film
thickness and consequently hydroplaning potential. These include:
Optimizing pavement geometry, especially cross-slope.
Providing some means of additional drainage, such as use of grooved
surfaces (PCC) or porous mixtures (HMA).
Including slotted drains within the roadway.
5. Tests Needed for Design. The design guidelines require an estimate of the surface
texture (MTD) and the coefficient of permeability Porous asphalt only). The sand
patch is an acceptable test method for measuring surface texture, except for the
more open (20-percent air voids) porous asphalt mixes. In these cases, an estimate
of the surface texture, based on tabulated data, is sufficient. As an alternative,
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sand patch measurements can be made on cast replicas of the surface. For the
open mixes, the glass beads flow into the voids within the mixture, giving an
inaccurate measure of surface texture.
Based on the measurements obtained In the laboratory, the coefficient of
permeability for the open-graded asphalt concrete does not exhibit a wide range of
values, and values of k may be selected for design purposes from tabulated design
data (k versus air voids). Given the uncertainty of this property resulting from
compaction under traffic and clogging from contaminants and anti-skid material, a
direct measurement (e.g., drainage lag permeameter) of k is not warranted.
Based on the previous discussion, no new test procedures are needed to adopt the
design guidelines developed during this project.
6. Grooving. Grooving of PCC pavements provides a reservoir for surface water and
can facilitate the removal of water if the grooves are placed parallel to the flow
oath. Parallel orientation is generally not practical because the flow on highway
pavements is typically not transverse to the pavement. Thus, the primary
contribution offered by grooving is to provide a surface reservoir unless the
grooves comlect with drainage at the edge of the pavement. Once the grooves are
filled with water, the tops of the grooves are the datum for the Why and do not
contribute to the reduction in the hydroplaning potential.
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7. Porous Pavements. These mixtures can enhance the water removal and Hereby
reduce water film tHch~ess. They merit more consideration by highway agencies
In the United States, but they are not a panacea for eliminating hydroplaning. As
with grooved PCC pavements, the internal voids do not contribute to the reduction
of hydroplaning; based on the field tests done In this study. hv~ronImiina can be
if, , , ~
expected on these mixtures given sufficient water fiLn thickness. Other than their
ability to conduct water through internal flow, the large MTD offered by porous
asphalt is the main contribution offered by the mixtures to the reduction of
hydroplaning potential. The high-void ~ > 20 percent), modified binder mixes used
In Europe merit further evaluation in the United States. They should be used In
areas where damage from freezing water and the problems of black ice are not
likely.
8. Slotted Drains. These fixtures, when installed between travel lanes, offer perhaps
the most effective means of controlling water film thickness from a hydraulics
standpoint. They have not been used extensively In the traveled lanes and
questions remain unanswered with respect to their installation (especially in
rehabilitation situations) and maintenance. The ability to support traffic loads and
still maintain surface smoothness has not been demonstrated and they may be
susceptible to clogging from roadway debris, ice, or snow.
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RECOMMENDATIONS AND CONCLUSIONS
The following recommendations are offered based on the work accomplished during
this project and on the conclusions given previously:
I. Implementation. The PAVDRN program and associated guidelines need to be field
tested and revised as needed. The program and the guidelines are sufficiently
complete so that they can be used in a design office. Some of the parameters and
algorithms will I~ely need to be modified as experience is gained with the
program.
2. Database of Material Properties. A database of material properties should be
gathered to supplement the information contained in PAVDRN. This information
should Include typical values for the permeability of porous asphalt and topical
values for the surface texture (MTD) for different pavement surfaces to include
toned Portland cement concrete surfaces. A series of photographs of typical
pavement sections and their associated texture depths should be considered as an
addition to the design guide (21.
3. Pavement Geometry. The AASHTO design guidelines (~) should be re-evaluated
In terms of current design criteria to determine if they can be modified to enhance
drainage without adversely affecting vehicle handling or safety.
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4. Use of appurtenances. Slotted drams should be evaluated In the field to determine
if they are practical when Installed In the traveled way. Manufacturers should
reconsider the design of slotted drains and their Installation recommendations
currently In force to maximize them for use In multi-lane pavements and to
determine if slotted drains are suitable for installations In the traveled right of way.
5. Porous Asphalt Mixtures. More use should be made of these mixtures, especially
the modified high a~r-void mixtures as used In France. Field trials should be
conducted to monitor HPS and the long-term effectiveness of these mixtures and to
validate the MPS and WDT predicted by PAVDRN.
6. Two-D~mensional Model. Further work should be done with two~mensional
models to determine if they improve accuracy of PAVDRN and to determine if
they are practical from a computational standpoint.
ADDITIONAL STUDIES
On the basis of the work done during this study, a number of additional items warrant furler
study. These Include:
1. Full-scale skid resistance studies to validate PAVDRN in general and the
relationship between water film thickness and hydroplaning potential in particular
are needed in light of the unexpectedly low hvdronlanin~ speeds predicted during
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this study. The effect of water infiltration into pavement cracks and loss of water
by splash and spray need to be accounted for In the prediction of water fihn
Sickness. Surface Irregularities, especially rutting, need to be considered in the
prediction models.
2. Field trials are needed to confirm the effectiveness of alternative asphalt and
Portland cement concrete surfaces. These include porous Portland cement concrete
surfaces, porous asphalt concrete, and various asphalt m~cro-surfaces.
3. The permeability of porous surface mixtures needs to be confirmed with samples
removed from the field, and the practicality of a simplified method for measuring
in-situ permeability must be investigated and compared to alternative
measurements, such as the outflow meter.
4. For measuring pavement texture, alternatives to the sand patch method should be
investigated, especially for use with porous asphalt mixtures.
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Representative terms from entire chapter:
portland cement
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