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Escalators have been a fixture in stations for over a century, playing a vital role in their daily operations. Their ability to efficiently move large numbers of people is crucial for managing passenger flow and ensuring smooth station function. Beyond daily operations, escalators are also a key component of emergency evacuation plans, possibly the only building typology where prescriptive basis accepts this. Why is this the case?
Please read more below:
The above code of practices, (Inc. ones for other Cites, Countries) are good reference point. However, Mass Transit escalators, lift and moving walkway usually require a higher specification
Shit happens!
A skilled designer not only crafts exceptional spaces, but also prioritizes the safety of the occupants. For an architect, integrating safety measures and considering human factors are indispensable prerequisites.
Escalators often become hotspots for accidents within our buildings. One safe solution is to implement the relevant code of practice of the land.
However is that enough? For transit station the answer is not so, due to many reasons, some of which are tabulated below:
In transit systems, the whole escalator assembly will be fire rated. Why? This is because NFPA 130.5.2.4 allows the floors to be connected, however if the escalator and stairs are fire rated, then the chance of fire spreading from one level to another is limited. Plus, historically many escalators have caught fire and have caused loss of life.
Escalator parts:
Upper equipment room houses the motor (Right) that drives the escalator drive belt
If the escalator rise is not much, the mid span support (Shown) may not be required.
The lower equipment room may not be require as machines are not housed here. There is a dry sump pit, if the pit is flooded, the lowest point (Which is the sump) will be used to evacuate the water with portable pump
ESCALATOR TYPES AND SPECIFICATIONS
ESCALATOR TYPES AND SPECIFICATIONS
Commentary on Escalator Classifications. Here we take the classification used in the Hong Kong MTR, for ease of reference + classification.
All escalators will have the drive machines (Motor) inside the truss. Called Machine in Truss (MIT)
Escalator will have their control panel inside the truss. Only accessible from the top of the truss This is Machine inside Truss, Control Inside (MIT/CI)
For the MIT type, you could have the control panel outside, so you undertake maintenance or control remotely. This is MIT/CO (Controller outside)
For a more robust system, you can put the drive (Motor) in their own room (Not pit), so that this can be accessed and maintained while the escalator is in operation. This is Machine Outside Truss (MOT)
Some Discussion on escalator features:
30 degree escalator pitch, a very good balance between many factors such as walkability, safety, space optimisation, plus it also allows a reasonable stairs tread and riser on the side, which can be the same angle
The flywheel at the newel ends allows the escalator handrail to more effectively turn around the newel ends, reduces wear and tear, plus reduces maintenance.
The remote control from the Station Control Room, enables the escalator to be stopped, direction reversed, if required, during evacuation. This is one of the prerequisites in NFPA 130, if you want to have more evacuation capacity.
The escalator needs to be fire rated as they MAY be placed between two fire compartments, most importantly they are a vital egress evacuation element and the must not burn - both within the truss and from the outside (As has been proved many times in the past).
Variable drive may save power substantially, Escalators are essentially a power hungry machines that is rated around 25kW, lowering the speed will save energy.
What gives? Why are the capacity of the escalators so different? Why is the HK Standards so high? (Or is it high?)
FYI------>
BS EN 115, Table H.1 denotes a max capacity of 8200 persons/hour
Let's do a simple escalator capacity calculation!
Let's do a simple escalator capacity calculation!
Escalator Width = 1m (Two people, side by side)
Escalator Speed = 0.75 M/S
Hence Escal capacity = 2 Ppl X 0.75m/s X 60 Sec
= 90 Ppl/min *
Design Standards followed by Operators (PPl/min)
Design Standards followed by Operators (PPl/min)
London LUL = 100 (O),
Singapore MRT = 120 (O, -10% =108)
HK MTR = 150/120 (O), 135 (E)
NFPA 130 = 55.5 (E)
BS EN 9992 = 120
Where:
O = Operation
E = Emergency
The HK Numbers
Yup. People are very busy and have no time to waste! So one side has people walking up, the other side standing.
Standing side capacity = 0.75m/s, OR 45 Ppl/min
Walking side capacity = 0.75m/s + 0.75m/s (Escal) X 60 = 90 Ppl/min
HENCE Total Escal Cap = 45 * 90 = 135 Ppl/min*
* Ok! Let me burst your bubble!
The above way may not be the right way to calculate the capacity. There is another basis, stemming from the human cone version. Or assumes that on one step, there are two people, on the next step, there is only one person. That way you have a acceptable density that passengers are comfortable on. The net result is that this gives a max capacity of 150ppl/min. The HK Standards comes from the practical test in metro systems (UK) and above cone basis, where 150ppl/min was recorded. This was then reduced down to 135ppl/min for emergency and 120 people for an operation scenario.
Second bubble burst.
There are other two scenario, in Hong Kong and many other systems, the tread width is 1m, however the tread depth is 0.4m and the height is 0.21m (Inclination of 30deg). In busy stations, there will be two passenger on each tread. Take a guess what is the overall capacity then?More than 214 ppl/min.
Now if you have person walking on one side, then the overall capacity is even higher, even if you provide a suitable reduction in the overall number.
So, from the bubble burst series on the left, or the above HK MTR guide to the passenger, what is the correct version or capacity for an escalator?
Many operators (Including HK MTR) consistantly ask for passenger NOT to walk on the escalators, to reduce not only to accidents on the escalator, but I assume to reduce the overall wear and tear. In the case of HK MTR, if socitally the passengers are happy to be closer on the escalator, not walking, then the design capacity and the operational capacity is closely matching.
However the London Tube has the highest escalator safety incidence compared to most systems. They also have one of the lowest escalator design capacity. So how does one define escalator safety?
Fig. Comparison of escalator capacity between different system and standards
ESCALATOR SAFETY
ESCALATOR SAFETY
SO ! Why does the Hong Kong MTR have such different standards?
That is a good question, it has many reasons:
Much more patronage than other systems. Pound per pound, the stations carries much more passengers.
Train headway is high, so escalators needs to work much more harder, to get the passengers off the platform, before the next headway.
Worse case emergency evacuation capacity high, escalator helps evacuation capacity calculation
People walk on escalator. For all of the above reasons, plus rise between floors in typical platform/concourse is ~6-7m, which is walkable.
People carry loads on the escalators (In the past 5 years, bollards have been installed, to stop this from happening, the cost of escalator maintenance + service disruption is too much), etc.
WHY DO YOU HAVE A QUEUING /RUNOFF IN FRONT OF AN ESCALATOR?
We walk at a speed of ~1.3m/s
Escalator speed = 0.75m/s
So, when you get on the escalator, you slowdown from 1.3m/s to 0.75m/s
when you get off an escalator, you need to reverse the speed, speed up.
Or if you are walking on the escalator, your resultant speed will be over 1.7m/s that you need to slow down.
Plus, there are many variables such as older people, mother & child, people with trolley, etc. using the escalator, which provides an impediment to smooth passenger movement, hence accidents happen, particularly on the escalator top areas.
The extended, clear run off in front of escalators help to give you that extra area, so that you have lots of areas to prepare to get on and off the escalator and then safely transition to a safe walking
ARE RUNOFF DISTANCE SAME IN DIFFERENT COUNTRIES? Nope!
UK = 8M**
SINGAPORE = 8M
HK = 12M
**(The UK TFL also requires additional dimension for variable length, say medium or high flow)
WHY ARE MOVING FLAT STEPS REQUIRED AND HOW MANY?
As noted above, to transition from walking to a moving steps, to a vertical movement of the escalator, & vice versa, the top & the bottom of the escalators in transit stations have extra steps, enhancing passenger safety & transition time
HK STANDARD REQUIRES 5 STEPS AT TOP AND 4 AT THE BOTTOM. (GLOBALLY AROUND 4, 4)
BTW! Transit station escalator have a high fire safety specs. Firstly, due to many historical fires both on, and inside the escalator. Further, to stop fire spread from the lower zone to the above!
Mind the Gap!
Ah! The gap between the escalator and the wall is another important safety issue.
One that is potentially a huge issue design if you want to keep the station width as narrow as possible. Particularly when VE bites and you want the escalator as tight as possible to the walls, etc......
Have a look at the below video to illustrate the issue and then work out what your city, country or their standards try and address this?
Or how you would address this, to bypass this.
FYI. All standards in many countries, including ASME A17.1 (U.S.) and EN 115 (EU) for escalators, including the above noted BS 5652-2, the Hong Kong EMSD CoP for Lift and Escalators,etc. all address the mininimum dimensional requirement between the handrail of the escalator and the side wall of the escalator, if they are not met, then one will need to install the ugly triangular head warning plastic deflectors.
SMARTER STATION PLANNING WITH BETTER VT SPREAD
SMARTER STATION PLANNING WITH BETTER VT SPREAD
Finally, on the escalator section, we do need to discuss the Vertical Transport (VT) disposition and the HK standard compared to other systems.
The top diagram is the HK Typology. ~8 cars, 4 banks of VT, all heading to the concourse above The uber patronage numbers, generally equal spread of the VT, including the mirrored VT configuration, the enhanced required runoff, the additional capacity of the escalators, all makes this transit system work much more efficiently to take the passengers on & off the platform.
Bottom diagram. Lesser number of cars, patronage, etc. Lower design standard may mean more escalator, however the higher headway, etc. allows for the disposition of these VT to work
Fig. Hong Kong MTR Platform VT disposition
Fig. Alternate Platform VT disposition. Escalator disposition entrance loaded
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