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Escalator Handling Capacity: Standards versus Practice
Article in Elevator World · December 1996
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ESCALATOR HANDLING CAPACITY: STANDARDS VERSUS PRACTICE
Dr. Lutfi Al-Sharif
London Underground Ltd.
Note: Published in Elevatori, Part I: Elevatori July/August
1996; Part II: Elevatori, September/October 1996, [in English
& Italian]. Reprinted in: Elevator World, December 1996, with
permission.
1. INTRODUCTION
The nominal handling capacity of a 1000mm wide escalator running at 0.75 m/s is
quoted in EN 115: 1995 as 13,500 passengers/hour. This is based on a factor of two
passengers per step. Although it is well known that this capacity is not achieved in
practice, different sources have quoted differing values for the actual capacity
achieved.
This article describes some surveys carried out on seven escalators to establish
their peak handling capacity, and also relates the results and compares them with the
work carried out by others.
2. STEP DIMENSIONS AND PASSENGER DIMENSIONS
As mentioned in the last section, the nominal capacity of a 1000 mm wide escalator
running at 0.75 m/s is quoted in EN 115: 1995 (CEN, 1995) as 13,500
passengers/hour. This assumes two passengers standing on each step. However, it
has been known that this capacity is not achievable in practice.
In some premises, the reasons for not achieving this capacity is very low
passenger flow rates (e.g., department stores). However, even in highly loaded
environments, with high peak flow rate (e.g., transport terminals), the maximum
handling capacity of the escalator is still not achieved. This articles sets out to show
that in practice the reasons for not achieving this nominal handling capacity is not due
to low passenger flow rates, but because of the relationship between the physical
dimensions of the passengers in relation to the physical dimensions of the steps and
the escalator.
On observing passengers boarding an escalator during queuing conditions, it is
noted that passengers on the standing side (right side) will board every other step,
while on the walking side (left side) will occupy every third step.
This phenomenon is related to the so-called human buffer zone. This is the
area which surrounds a person, and leads people to avoid touching each other. As we
all know, it is very uncomfortable to be standing with one’s face on the next person’s
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back. The human buffer zone is larger than the area offered by the depth of one step 1.
This human buffer zone is a concept developed by Fruin, and represents the area
which people will try to keep free (unless forced to do so by crowding on a train for
example). It has also been termed as the human ellipse, and is shown in Figure 1.
Breadth
24''
(610mm)
Depth
18''
(457mm)
Figure 1: The human ellipse (reproduced from Fruin, 1987, p67).
We can compare this ellipse to the effective step projection, shown in Figure 2 and in
Figure 3. The effective depth of the step is smaller than the physical depth because of
the curvature of the step. It is clear from the two figures that the depth of the ellipse is
larger than the effective depth of the step. Moreover, the width of the step is not
sufficient to accommodate two passengers side by side. This explains why it is
uncomfortable to walk past standing passengers.
Sd
Se
30
Sh
Figure 2: Step dimensions, showing step depth (Sd), step height (Sh) and
effective step depth (Se).
1
When we talk about the depth of one step we should talk about the effective depth rather than the
literal depth. The step overlap causes the effective step depth to be 400 mm x cos 30° which is equal to
346 mm, and not 400 mm.
2
S e (364mm)
Sw
(1000mm)
Figure 3: The effective dimensions of a step.
Figure 4: The profile of two passengers side by side super-imposed on the step
projection.
Figure 4 shows the profile of two passengers side by side super-imposed on a number
of steps (the step projection shows the effective step depth). As seen from the figure,
if the buffer zone around the passengers is taken into consideration, then it is not
possible for passengers to comfortably stand side by side and on every step, or to
board consecutive steps.
3. WALKING ON ESCALATORS
The nominal capacity on an escalator usually assumes stationary passengers.
However, walking passengers will increase the flow rate on an escalator. This section
sets out to account for this effect by formulating a factor called the walking factor,
which can be used to arrive at the effective handling capacity of an escalator. This
factor depends on the speed of walking passengers and on their percentage compared
to the total number of passengers on the escalator. Moreover, this factor changes
throughout the day, as it depends on the percentage of passengers who walk and the
speed at which passengers walk in different periods of the day.
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3.1 Walking speeds on escalators
The average speed of a walking passenger on stairs is shown in Table 1, reproduced
from Fruin.
Table 1: Average walking speeds on stairs (Fruin, 1987, p 56).
Angle of inclination
32 degrees
27 degrees
Down direction
132 (ft/min)
152 (ft/min)
Up direction
100 (ft/min)
113 (ft/min)
If these figure are interpolated for an anle if inclination of 30 degrees, the resulting
figures, converted in m/s, are
Down: 0.71m/s
Up:
0.53 m/s
Andrews & Boyes (1977, p 36) in a study carried out at Victoria station, calculated the
following figures for walking speeds on 30 degree escalators:
Down: 0.66 m/s
Up:
0.63 m/s
3.2 Walking Percentage of passengers
Andrews & Boyes (1977, p27) also found that the percentage of walking passengers to
total passenger in off peak periods was 40% for down traffic, and 20% for up traffic.
During peak periods this rose to 60% for down traffic and 40% for up traffic. This is
summarised in the following table.
Period
Off-Peak period
Peak period
Down traffic
40%
60%
Up Traffic
20%
40%
3.3 Walking Factor
Using these figures, and assuming an escalator speed of 0.75 m/s, the walking factors
for various scenarios can be calculated as follows:
Table 2: Walking factors for various situations.
Off-Peak period
Peak Period
Down Traffic
0.74
0.66
Up Traffic
0.86
0.75
For simplicity, a constant factor of 0.7 can be assumed in all the calculation. To find
the effective capacity, multiply the capacity with passengers standing and divide it by
the factor above.
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4. THE SURVEYS
In order to validate the previous theoretical calculations, passenger surveys were
examined to compare to these figures. The surveys were actually carried out for a
completely different study.
Passenger surveys were only carried out on seven escalators, which were
classified as high usage (i.e., more than 11,000 passengers per day). The counts were
carried out in 30 seconds intervals, by one group of observers situated at one end of
the escalator (either the top or bottom depending on the physical constraint). A one
minute sampling interval was deemed sufficient to give good accuracy, as opposed to
the original proposition of using a 30 second interval.
Table 3 shows the number of passengers using each of the seven escalators per
day, along with the rise of each in metres. The results of the surveys are shown in
Table 4, which are the maximum peak flows recorded in one minute.
Table 3: Number of passengers per day using the seven escalators.
Escalator number
Escalator D
Escalator E
Escalator A
Escalator B
Escalator C
Escalator F
Escalator G
Rise (m)
7.623
7.623
14.630
14.630
14.630
17.221
17.221
Usage (pass/day)
22456 (U)
24910 (D)
27825 (U)
27825 (U)
52622 (D)
12179 (U)
17696 (D)
It general it can be seen that down escalators carry more passengers than up escalators.
Table 4: Maximum passenger flows measured on the seven escalators.
A
Actual maximum
measurement
(pass/min.)
Percentage of
theoretical capacity
B
C
D
E
F
G
101
104
140
122
123
86
92
45%
46.2%
62.2%
54.2%
54.7%
38.2%
40.9%
In general it can be seen that the actual maximum flow is around 55% of 13,500
passengers per hour, or 7425 passengers/hour which is the equivalent of 124
passengers/minute.
5. HANDLING CAPACITY
As discussed in the last section, even on escalators where queues are developing and
severe crowding is taking place at the landing, passengers will still board every other
step on the right (standing) side and board every third step on the left (walking) side.
Thus the standing side is 50% utilised, while the walking side is 33% utilised. This
leads to the important result:
5
1 1 1 1
× + ×
= 41. 7% = 5630 pass / hour
2 2 2 3
Thus, the maximum capacity of a 1000 mm wide 0.75 m/s escalator, is 41.7% of
13,500 passengers per hour, 5630 passengers/ hour or 94 passengers/minute. This is
underestimating the fact that passengers on the walking side are travelling faster than
0.75 m/s (because their speed is added to the speed of the escalator). In other words,
this is assuming stationary passengers and is not taking into account of the walking
factor mentioned previously.
To account for the walking factor, and assuming a constant factor of 0.7, the
effective capacity can be calulated as follows:
Effective capacity= 5630/0.7= 8042 passengers/hour, or 134 passengers/minute.
Maximum Actual Capacity =
This figure fits with the observed capacity on the seven escalators, taking into
consideration that the counts were carried out in peak times, and the group of
escalators included up as well as down running escalators.
This actual capacity is confirmed by other sources, as discussed in the following subsections.
5.1 Fruin’s “empty step” phenomenon
Fruin carried out an excellent analysis of escalator capacity (Fruin, 1987, p 96-105).
He attempted to explain the “Numerous observations have shown that 100 per cent
utilisation is never obtained, even with the heaviest traffic pressure and use by the
most knowledgable and agile pedestrians, including commuters.....Actual capacity is
considerably lower...and is generally one person per step on a 48 inch wide escalator
[nominal 40 inch or 1016 mm] (Fruin, 1987, p 97-98).”
Based on this one passenger per step observed capacity, He then quotes such
capacity as 90 passengers/ minute assuming one passenger per step on a 1000 mm
wide escalator running at a speed of 120 feet / minute (0.61 m/s) (Fruin, 1987, p98),
which if adjusted to a speed of 0.75 m/s, will come out as 111 passengers/ minute.
He then adds: “Although these nominal capacity ratings provide a useful
guideline for comparing escalator sizes and speeds, they do not explain the
phenomenon of empty steps that are often seen when escalators are under heavy use,
nor the wide variations in capacity that have been reported by various agencies....The
real deteminants of this use (i.e., escalator usage) are the arrival process, and boarding
characteristics of the uses. (p 99)”
He then uses the concept of the buffer zone between passengers to explain
empty step problem. “Personal area preference, therefore, provides a partial
explanation of the phenomenon of vacant steps on escalators in heavy traffic. When
boarding an escalator, a person has the option of choosing a step position directly
behind and beside another person, with the risk brushing against him or her, or letting
that step go by, thus obtaining a more comfortable personal space. This prospect of
leaving a gap would depend on the individual’s own buffer zone image, the physical
size of adjacent persons, or the presence of baggage or packages (p 100).”
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5.2 Other sources
London Underground Station Planning Guidelines quote a similar figure of 100
passengers/ minute for a 1000 mm wide escalator (and it implicitly assumes it is
running at 0.75 m/s) (London Underground Ltd., 1995, section 5.6.8).
Mayo showed that the optimum escalator speed to achieve a maximum
handling capacity was 0.75 m/s and that the maximum capacity achieved at that speed
was 135 passengers/minute, assuming a constant flow rate of 5500 passenger/hour
(Mayo, 1966, p58).
Relationship between escalator speed and
handling capacity.
135.00
Pass/min
130.00
125.00
120.00
115.00
100
110
120
130
140
150
160
170
180
Speed (ft/min)
Figure 5: Relationship between escalator speed and handling capacity (Mayo,
1966, p58).
6. CONCLUSIONS
The actual escalator handling capacity is 42% of the theoretical capacity quoted in BSI
and CEN standards. If the fact that passengers walk is taken into consideration, this
figure rises to around to a maximum of 60%. In order to account for the difference
between walking and standing, a walking factor has been derived which varies
between off peak and peak periods and between up and down directions. The value of
this factor is around 70% (i.e., 0.7).
The main reason for this theoretical capacity not being achieved, is the fact
that the human buffer zone (the so-called human ellipse) is larger than the effective
step dimensions.
BIOGRAPHICAL NOTES
The author graduated in electrical engineering in 1987, and then worked as an
electronic design engineer for lift logic and speed controllers for two years. He
received his M.Sc. in 1990, his Ph.D. in 1992 from UMIST, and his D.B.A. from the
University of Westminster in 1995. He joined London Underground in the Lift &
Escalator Department in 1992, and is currently Team Leader for Lift Projects and
Electrical Design. He writes regularly in Elevatori, Elevation and Lift Report, and is a
Chartered Electrical Engineer.
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REFERENCES AND BIBLIOGRAPHY
Andrews, J.M. & Boyes, J.V.J., 1977, “Pedestrian movement at Victoria
Underground station”, 1977/1978, University College London.
CEN, 1995, “Safety rules for the construction and installation of escalators and
passengers conveyors”, EN 115: January 1995.
Fruin, J.J., 1987, “Pedestrian planning and design”, Revised Edition, 1987, Elevator
World, Inc., Educational Services Division.
London Underground Ltd., 1995, “LUL station planning guidelines”, April 1995.
Mayo, A.J., 1966, “A study of escalators and associated flow systems”, M.Sc. Degree
Report, Imperial College of Science and Technology (University of London),
September 1966.
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