Airport Pavement Roughness with Nighttime Construction

Gordon F. Hayhoe

Federal Aviation Administration, William J. Hughes Technical Center,
AAR-410

USA

Mingyao Dong

Galaxy Scientific Corporation, Egg Harbor Township, NJ

USA

Roy D. McQueen

Roy D. McQueen & Associates, Ltd., Oakton, VA

USA

# ABSTRACT

Surface elevation profiles were measured before and after overlay
operations on runways at two commercial airports in the USA. Each
airport had only one runway. All overlaying was done at night, with the
airports opened for normal operations during the day. The profiles were
measured with an inertial profiler having software compensation for
accelerometer errors. Pavement surface elevations measured with normal
surveying rod and level equipment are compared with the profiler
elevation measurements for one of the runways. With the exception of
some very long wavelength distortion in the profiler measurements,
correspondence between the two different methods is good. The profiles
were processed to provide measures of roughness from simulations of a
straightedge, a California Profilograph, and the Boeing Bump Criteria.
The roughness of the overlaid pavements is quantified and compared.
Measurements of the vertical response of an instrumented B-727 aircraft
on one of the runways are also presented. Transverse construction joints
are shown to be significant contributors to the roughness of the
pavements.

# INTRODUCTION

Pavement maintenance and rehabilitation at commercial airports has to be
performed with minimum disruption of aircraft service. For large
international airports, and for airports with only one runway, this
almost always means that major pavement work, such as overlaying and
rehabilitation, must be done at night in a series of short "pulls." The
pressure of rapid work, combined with frequent lateral construction
joints, can lead to runways which are not as smooth as can be achieved
when the runway is completely shut down and the work is done
continuously. In order to make a determination of the levels of
roughness which are achieved during intermittent construction, two
runway overlay rehabilitation projects were selected for study.

The first (referred to here as R1) was a flexible pavement which was
structurally sound but had suffered surface deterioration due,
primarily, to cracking and weathering. To restore the surface, a nominal
75-mm (3-inch) overlay was applied to controlled grade. The second (R2)
was a very old rigid pavement which had been lightly overlaid to seal
the surface until the runway could be rehabilitated. Rehabilitation
consisted of a crack-and-seat operation followed by application of a
nominal 200-mm (8-inch) thick overlay. Construction was phased, with
625-m (2,000-ft) sections at each end of the runway constructed during
the daytime using displaced thresholds. The 2,500-m (8,000-ft) center
section of the runway was then re-constructed at night in a series of
7-hour closures. During the nighttime operations on both of the runways,
the overlays were placed over the full width in a single night in pull
lengths of 100 to 150 m (300 to 450 ft).

Elevation profiles of the two runways were measured before and after the
construction operations using an inertial profiler. The profiler was
developed under FAA funding specifically for rapid

measurement of elevation profiles on airport runways and taxiways. The
equipment is portable so that it can be easily transported as aircraft
baggage. Distance to the pavement surface is measured with a small
spot-size laser sensor at a very high data rate so that lateral grooving
can be measured and, where necessary, correctly filtered out of the
profile. Vertical (inertial) position of the test vehicle is found by
open loop integration of the vertical accelerometer signal. Stabilizing
compensation is applied in the data processing software using a
least-squares minimization scheme. Errors in the vertical accelerometer
signal due to acceleration and braking of the test vehicle are also
compensated for as part of the minimization scheme. Use of the
compensation eliminates the need to stabilize the integration process by
high-pass filtering, as is normally done with highway profile
measurements (Pong, 1991). Distortion of the profile over long
disturbances is therefore reduced and it is easier to visually identify
specific disturbances in the measured profile. Rod and level survey
measurements made prior to overlaying runway R1 were also obtained from
the construction contractor.

Roughness indices were computed from the measured profiles to evaluate
the change in roughness from before to after the paving operations, and
to make a determination of the levels of roughness which were achieved
during the operations. Indices computed were 3.7 m (12-ft) straightedge,
California Profilograph, and an adaptation of the Boeing Bump Criteria
(DeBord, 1992).

## PROFILE MEASUREMENT

A typical inertial profiler consists of three major components: a sensor
to measure the distance from a point on the test vehicle to the pavement
surface; an accelerometer to measure the vertical acceleration of the
test vehicle; and a sensor for measuring the distance traveled along the
pavement.

The profiler that was used has a laser triangulation-type distance
measuring sensor with a nominal spot size of 1 mm (0.04 in), a
measurement range of ± 100 mm (4 in), a resolution of 12-bits (0.049 mm,
0.002 in), and a sample rate of 32 kHz. The normal test speed is 60 km/h
and the maximum spatial sampling distance is therefore 0.52 mm/sample
(0.02 in/sample), or one-half the spot size per sample. (There will also
be more than 10 samples taken while traversing a 6-mm groove.)

![](media/image1.wmf)        A high quality servo accelerometer measures
the vertical acceleration of the test vehicle and a non-contact
incandescent light distance sensor measures traveled distance (output is
one pulse every 2.5 mm (0.1 in)). Inertial profiling devices were
originally developed for highway use and measurements with these devices
are typically made at a constant travel speed. However, runways and
taxiways normally have closed ends and, in order to measure the profile
along the full length of a runway or taxiway, measurements must be made
while the test vehicle is accelerating or braking. This can introduce
extremely large errors into the profile measurement. (High-pass
filtering the profile will not remove the errors unless a very short
cutoff wavelength is used.)

        Figure 1 illustrates how the errors arise. The sensitive axis of
the accelerometer is usually inclined at some small angle *(θ)* to the
desired measurement axis (which is perpendicular to the pavement
surface). In addition, a change of inclination angle *(δ)* also occurs
whenever the test vehicle pitches under acceleration or braking. Because
of the inclination of the accelerometer to the pavement surface, a
component of the longitudinal acceleration of the test vehicle is
coupled into the sensitive axis of the accelerometer, causing
significant errors if the vehicle accelerates or brakes. Using the
nomenclature:

  ------------------------------------------------- ------------------------------------------------------------
  $$\theta$$                                        = initial accelerometer angle offset perpendicular to the
                                                    pavement surface.

  $$\delta$$                                        = vehicle pitch angle from initial offset position.

  $$\overset{¨}{z}$$                                = vehicle acceleration perpendicular to the pavement surface
                                                    (bounce).

  $$\overset{¨}{x}$$                                = vehicle acceleration parallel to the pavement surface
                                                    (acceleration and braking).

  $$\overset{¨}{z}\ \text{cos}(\theta + \delta)$$   = component of vertical acceleration along the sensitive
                                                    axis.

  $$\overset{¨}{x}\ \text{sin}(\theta + \delta)$$   = component of longitudinal acceleration along the sensitive
                                                    axis.
  ------------------------------------------------- ------------------------------------------------------------

The acceleration measured by the accelerometer along its sensitive axis
can be written as:

$${\overset{¨}{z}}_{M} = \overset{¨}{z}\ \text{cos}\ (\theta + \delta) - \overset{¨}{x}\ \text{sin}\ (\theta + \delta\ )$$

The initial offset and pitch angles are small and, using the small angle
approximations $\text{cos}\alpha \approx 1$
and$\text{sin}\alpha \approx \alpha$:

$${\overset{¨}{z}}_{M} = \overset{¨}{z} - \overset{¨}{x}\theta - \overset{¨}{x}\delta$$

If it is further assumed that the pitch angle of the vehicle relative to
the pavement surface is a linear function of longitudinal acceleration
relative to the pavement surface, then:

$$\delta = C\ \overset{¨}{x}\text{, and  \{}\overset{¨}{x}\delta = C\ {\overset{¨}{x}}^{2}$$

where *C* is a constant of proportionality with units of radians/m/s^2^.

Including an offset for gravity and drift in the instrumentation
electronics, ${\overset{¨}{z}}_{0}$, the measured acceleration is given
by:

$${\overset{¨}{z}}_{M} = {\overset{¨}{z}}_{0} + \overset{¨}{z} - \overset{¨}{x}\theta - C\ {\overset{¨}{x}}^{2}$$

and, rearranging the equation, an approximation of the true vertical
acceleration is:

$$\overset{¨}{z} = {\overset{¨}{z}}_{M} - {\overset{¨}{z}}_{0} + \overset{¨}{x}\theta + C\ {\overset{¨}{x}}^{2}$$

Note that the term associated with initial pitch angle, *θ*, changes
sign with $\overset{¨}{x}$, whereas the term associated with pitch
change always has the same sign. Vertical velocity is now found by
integration:

$$\begin{array}{r}
\overset{˙}{z} = {\overset{˙}{z}}_{0} - \int_{}^{}{\overset{¨}{z}}_{0}\text{.}\text{dt} + \int_{}^{}{{\overset{¨}{z}}_{M}\text{.}\text{dt} + \theta\int_{}^{}{\ \overset{¨}{x}\text{.}\text{dt} + C\int_{}^{}{\ {\overset{¨}{x}}^{2}\text{.}\text{dt}}}} \\
{\overset{˙}{z}}_{0} - {\overset{¨}{z}}_{0}\ t + {\overset{˙}{z}}_{M} + \overset{˙}{x}\ \theta + {\overset{˙}{z}}_{S}C
\end{array}$$

where ${\overset{˙}{z}}_{0}$ = vertical velocity at *t* = 0 and
${\overset{˙}{z}}_{S} = \int_{}^{}{\ {\overset{¨}{x}}^{2}\text{.}\text{dt}}$.

All quantities are sampled at time increments of ∆ seconds and all data
processing is done digitally. Therefore, the equation for vertical
velocity can be rewritten in terms of the sample index, *i*, and
numerically integrated quantities, with the first sample numbered 0:

$${\overset{˙}{z}}_{i} = {\overset{˙}{z}}_{0} - i\Delta\text{.}{\overset{¨}{z}}_{0} + {\overset{˙}{z}}_{Mi} + {\overset{˙}{x}}_{i}\ \theta + {\overset{˙}{z}}_{Si}C$$

Adjusting ${\overset{˙}{z}}_{0}$, ${\overset{¨}{z}}_{0}$, *θ*, and *C*
so that ${\overset{˙}{z}}^{2}$ is minimized over the full length of a
digitized profile record proved to be a reasonable strategy for removing
the majority of the errors due to acceleration coupling as well as for
stabilizing the integration process. Therefore, following the normal
procedure for computing least squares coefficients (Press, 1992) gives:

$$\sum_{}^{}{\overset{˙}{z}}_{i}^{2} = \sum_{}^{}\left( {\overset{˙}{z}}_{0} - i\Delta\text{.}{\overset{¨}{z}}_{0} + {\overset{˙}{z}}_{Mi} + {\overset{˙}{x}}_{i}\ \theta + {\overset{˙}{z}}_{Si}C \right)^{2} = \text{minimum}$$

Differentiating with respect to ${\overset{˙}{z}}_{0}$,
${\overset{¨}{z}}_{0}$, *θ*, and *C* in turn and equating the resulting
expressions to zero gives the following matrix equation (where *N* = the
total number of samples):

$$\begin{pmatrix}
\ N & - \Delta \sum_{}^{}i & \sum_{}^{}{\overset{˙}{x}}_{i} & \sum_{}^{}{\overset{˙}{z}}_{Si} \\
 - \Delta \sum_{}^{}i & \Delta^{2}\sum_{}^{}i^{2} & - \Delta \sum_{}^{}{i\ {\overset{˙}{x}}_{i}} & - \Delta \sum_{}^{}{i\ {\overset{˙}{z}}_{Si}} \\
\sum_{}^{}{\overset{˙}{x}}_{i} & - \Delta \sum_{}^{}{i\ {\overset{˙}{x}}_{i}} & \sum_{}^{}{\overset{˙}{x}}_{i}^{2} & \sum_{}^{}{{\overset{˙}{x}}_{i}{\overset{˙}{z}}_{Si}} \\
\sum_{}^{}{\overset{˙}{z}}_{Si} & - \Delta \sum_{}^{}{i\ {\overset{˙}{z}}_{Si}} & \sum_{}^{}{{\overset{˙}{x}}_{i}{\overset{˙}{z}}_{Si}} & \sum_{}^{}{\overset{˙}{z}}_{Si}^{2}
\end{pmatrix}\begin{pmatrix}
{\overset{˙}{z}}_{0} \\
{\overset{¨}{z}}_{0} \\
\theta \\
C
\end{pmatrix} = \begin{pmatrix}
 - \sum_{}^{}{\overset{˙}{z}}_{Mi} \\
\Delta \ \sum_{}^{}{i\ {\overset{˙}{z}}_{Mi}} \\
 - \sum_{}^{}{{\overset{˙}{x}}_{i}{\overset{˙}{z}}_{Mi}} \\
 - \sum_{}^{}{{\overset{˙}{z}}_{Si}{\overset{˙}{z}}_{Mi}}
\end{pmatrix}$$

The matrix equation is solved after all of the summations have been
computed over the full record length. The procedure is only applicable
for a record of reasonable length. (Other similar but more complicated
procedures are available for real-time processing of such signals. But
they would probably not be suitable for the present application because
of the comparatively short records and the rapid changes in conditions
(Stengel, 1994, and Press, 1992).) Integrating the corrected vertical
velocity, $\overset{˙}{z}$, adding the displacement sensor signal, and
applying a linear correction to give the start and end points the same
value (usually zero) completes the computation of the elevation profile
with respect to time. The profile is converted to a spatial record by
low-pass filtering and then eliminating all data points except for those
occurring closest to each tenth traveled distance pulse. Final sample
spacing is therefore 25 mm (1 in). A scheme in which the elevation
sample values are averaged between distance pulses is used when the
vehicle speed falls below the point where serious aliasing of the
decimated signal would occur.

As an example of the effects of the processing, figures 2 through 9
below show results for a profile measurement made 3 m (10 ft) to the
right of the center line of Runway R1 before the runway was overlaid.
The normal test procedure is to align the test vehicle at the runway
threshold, accelerate to the test speed, travel the majority of the
length of the runway under cruise control, and brake to a full stop at
the opposite threshold. But in this case a construction truck crossed
the runway during the measurement and the driver of the test vehicle was
forced to brake and then accelerate back to the test speed. With no
compensation applied to the accelerometer signal, except to force the
end-points of the velocity and position signals through zero, extreme
errors are apparent during the periods when the vehicle is accelerating
or braking. Also note the asymmetry of the errors in the velocity signal
caused by the combination of linear and squared terms in the error
equation, mentioned above.

The calculated total vertical motion of the vehicle is 6.2 m (20.4 ft)
compared to the corresponding distance measured by a rod and level
survey of 0.6 m (1.9 ft) (see figure 9). But after applying the
compensation scheme, the vertical velocity signal has a much smaller
range and the rapid changes associated with the acceleration and braking
of the test vehicle have been reduced to the extent that they cannot be
visually distinguished from the rest of the signal except, perhaps, at
the very end of the record. Calculated total vertical motion has been
reduced to 0.3 m (1 ft). This is less than was measured in the rod and
level survey; an effect caused by minimizing vertical velocity squared
about the straight line connecting the ends of the profile. Curves fit
through a few coarsely spaced points along the pavement can be used as
the minimization datum to generate detailed profiles much closer to the
true absolute profile.

![](media/image2.png){width="6.25625in" height="1.1409722222222223in"}

Figure 2.  Test vehicle speed, ft/s, total record length = 114.65
seconds. (CHO103R1.PRO)

![](media/image3.png){width="6.25625in" height="1.1409722222222223in"}

Figure 3.  Vertical velocity of the test vehicle at the accelerometer,
no compensation, in/s.

![](media/image4.png){width="6.25625in" height="1.1409722222222223in"}

Figure 4.  Vertical (inertial) position of the test vehicle at the
accelerometer, no compensation, in.

![](media/image5.png){width="6.25625in" height="1.1409722222222223in"}

Figure 5.  Vertical velocity of the test vehicle at the accelerometer,
full compensation, in/s.

![](media/image6.png){width="6.25625in" height="1.1409722222222223in"}

Figure 6.  Vertical (inertial) position of the test vehicle at the
accelerometer, full compensation, in.

![](media/image7.png){width="6.25625in" height="1.1409722222222223in"}

Figure 7.  Elevation profile with respect to time, full compensation,
in.

![](media/image8.png){width="6.25625in" height="1.1409722222222223in"}

Figure 8.  Elevation profile with respect to distance, full
compensation, in. Total length = 1,667 m (5,469 ft).

![](media/image9.png){width="6.25625in" height="1.1409722222222223in"}

Figure 9.  Rod and level survey, in, at 7.62 m (25 ft) spacing along the
centerline of the runway.

**BEFORE AND AFTER ON RUNWAY R1**

Profiles were also measured on Runway R1 after the overlay had been
placed. Figures 10 and 11 show the deviations from a simulated 3.6-m
(12-ft) straightedge computed for profiles measured 3 m (10 ft) from the
centerline of the runway. The deviations were computed once every 25 mm
(1 in) along the profile. The difference in the record lengths was
caused by construction signs which were erected prior to overlaying of
the pavement and which obstructed the ends of the runway. Probability
distribution functions were also computed (figure 12) and the 85th
percentile deviations (85%) determined. By these measures, the pavement
on that profile line became rougher as a result of the overlaying
operation. However, with one exception on the overlaid pavement, the
measurements are well within FAA advisory standards. The exception is a
computed deviation from the straightedge of approximately 17 mm (0.65
in). A zoomed view of the profile, with the straightedge and deviation

![](media/image10.png){width="6.25625in" height="1.1409722222222223in"}

Figure 10.  Straightedge before overlay, average = 1.4 mm (0.05 in), 85%
= 2.1 mm (0.083 in).

![](media/image11.png){width="6.25625in" height="1.1409722222222223in"}

Figure 11.  Straightedge after overlay, average = 1.9 mm (0.075 in), 85%
= 2.7 mm (0.11 in).

![](media/image12.png){width="2.6354166666666665in"
height="2.71875in"}![](media/image13.png){width="2.6347222222222224in"
height="2.71875in"}

line included, is shown in figure 13. The cause of the large deviation
is a change in elevation height of 14 mm (0.55 in) over a distance of
1.4 m (4.75 ft). (The extreme deviation occurs with the straightedge
further to the left, but the position in the figure shows the problem
area more clearly.) Visual inspection of the pavement showed that the
disturbance was caused by a poorly formed transverse joint extending
across about one quarter the width of the runway. Figures 14 and 15 show
computed displacements of the measuring wheel of a simulated 12-wheel
California Profilograph for the same profiles. A +/- 2.54 mm (0.1 in)
blanking band is also shown. The results are very similar to those for
the straightedge except that the relative magnitudes of the pavement
disturbances are, in some cases, quite different. (see ACPA, 1990, for
the definition of PI). The large indicated disturbance toward the left
end of the runway is due to a drop in the pavement of 28 mm (1.1 in)
over approximately 6 m (20 ft) followed by a shallower rise. These
distances along the pavement are longer than the straightedge length but
about the same order as the length of the profilograph. The disturbance
would therefore not be expected to be as prominent on the straightedge
record.

![](media/image14.png){width="6.25625in" height="1.1409722222222223in"}

Figure 13.  Zoomed profile corresponding to figure 11 and with
straightedge included.

![](media/image15.png){width="6.25625in" height="1.1409722222222223in"}

Figure 14.   Profilograph before overlay, PI = 2.3 in/mile.

![](media/image16.png){width="6.25625in" height="1.1409722222222223in"}

Figure 15.  Profilograph after overlay, PI = 4.7 in/mile. (CHO203R1.PRO)

**AFTER OVERLAYING ON R2**

Profile measurements were also made on Runway R2 before and after
overlaying. However, except to say that roughness increased somewhat on
this runway as well, only the roughness of the pavement measured after
overlaying will be discussed. Figure 16 shows a profile measured
approximately 1 m (3 ft) to the side of the centerline. Figures 17 and
18 show straightedge and profilograph plots respectively. The runway is
much rougher than Runway R1 except at the ends, which were completely
closed when that part of the runway was overlaid. The 85^th^ percentile
straightedge deviation, at 5.3 mm (0.21 in), is close to the FAA
advisory maximum. Over smaller sections, the limit may be exceeded,
although it should be said that the procedure for computing the 85^th^
percentile is quite different than the manual method and a correlation
between the two methods has not been made. The Boeing Bump criteria is
shown in figure 19 for comparison with an index which tends to favor
longer length disturbances (a pavement is rated unsatisfactory by the
Boeing criteria when the bump index exceeds a value of 1). Very distinct
disturbances are identifiable at the same positions on all of the plots.
These disturbances are typically associated with transverse joints.
Measurements were also made of the response of an instrumented
B-727-100QC aircraft operated by the FAA William J. Hughes Technical
Center. Figures 20 through 24 show the vertical accelerations and
vertical strut loads for a run made with a maximum speed of 100 knots.
The nose gear responses marked in figure 23 correspond with the pavement
disturbances marked in figure 17. Maximum accelerations measured at the
cg and the cockpit are both close to, or above, the generally accepted
maximums for aircraft ride quality. However, the measurements were made
at a sample rate of 240 Hz and were low-pass filtered with a cutoff
frequency of 10 Hz. Changing the filter frequency will make a
considerable difference to the magnitudes of the measured maximum
accelerations. Specifications for limits on allowable maximum
accelerations should include details on the intended bandwidth of the
aircraft responses to be measured and on the signal processing
requirements.

![](media/image17.png){width="6.25625in" height="1.1409722222222223in"}

Figure 16.  Profile on Runway R2 measured after overlaying.
(MD3101C1.PRO, copy to R2.PRO)

![](media/image18.wmf)Figure 17.  Straightedge on Runway R2, average =
3.5 mm (0.136 in), 85% = 5.3 mm (0.21 in).

![](media/image19.png){width="6.25625in" height="1.1409722222222223in"}

Figure 18.  Profilograph on Runway R2. PI = 21.3 in/mile over the full
length. For 300 m (1,000 ft) section lengths PI varies from 7 at the
ends to 34 for the section containing the largest disturbance.

![](media/image20.png){width="6.25625in" height="1.1409722222222223in"}

Figure 19.  Boeing Bump Index on Runway R2.

![](media/image21.png){width="6.25625in" height="1.011111111111111in"}

Figure 20.  B-727 aircraft speed, ft/s (1 ft/s = 0.3048 m/s). Target
speed was 100 knots (168 ft/s).

![](media/image22.png){width="6.25625in" height="1.011111111111111in"}

Figure 21.  B-727 aircraft: vertical acceleration at the center of
gravity (g), on the cabin floor.

(HRT100.DAT, before grind)

![](media/image23.png){width="6.25625in" height="1.011111111111111in"}

Figure 22.  B-727 aircraft: sum of left and right main gear strut
vertical loads.

![](media/image24.wmf)Figure 23.  B-727 aircraft: nose gear strut
vertical loads.

![](media/image25.png){width="6.25625in" height="1.011111111111111in"}

Figure 24.  B-727 aircraft: vertical acceleration at the cockpit floor.

**CONCLUSIONS**

Suitable procedures and equipment have been developed for rapidly
measuring airport pavement elevation profiles and computing roughness
indices from the measured profiles. The index variables (deviation from
a straightedge, for example), when plotted over the full length of a
runway or taxiway, provide a convenient means of identifying possible
rough areas and evaluating strategies for remediation.

Overlaying airport pavements during nightly closures can result in
rougher pavements than would normally be expected because of the large
number of lateral construction joints necessitated by this type of
schedule. Measurements were made on two asphalt overlay projects, with a
significant difference being shown between the roughness of the
resulting pavements. Construction practices used during the nightly
startup and close-down phases clearly play an important role in the
quality of the pavement surfaces. However, other differences between the
two projects, both structurally and procedurally, may play equally
significant roles and more evaluation is required before drawing further
conclusions. It should also be noted that the projects were selected for
evaluation before rehabilitation began.

**ACKNOWLEDGEMENTS**

The work described in this paper was conducted under FAA contract No.
DTFA03-93-C-00021, William J. Hughes Technical Center, Atlantic City,
NJ, USA, COTR Satish K. Agrawal.

**REFERENCES**

**Pong, Meau-Fu and Wambold, J.C.**, "Evaluation of Accelerometer
Established Inertial Profiling Reference Computation Methods," 71^st^
Annual Meeting of the TRB, Washington, DC, USA, 1991.

**Stengel, R.F.**, "Optimal Control and Estimation," Dover Publications,
Mineola, NY, USA, 1994.

**Press, H.P., Teukolsky, S.A., Vetterling, W.T. and Flannery, B.P.**,
"Numerical Recipes in FORTRAN," Cambridge University Press, 1992.

**ACPA**, "Constructing Smooth Concrete Pavements," Technical Bulletin
TB-006.0-C, 1990.

**DeBord, K.J.**, "Runway Roughness Measurement, Quantification, and
Application - the Boeing Method," Boeing Document No. D6-81746, Boeing
Commercial Airplane Company, USA, 1990.