Why I created the “PLAI Score” — a simple way for homebuyers to judge lift adequacy in high-rise buildings

Over the past few months, I’ve seen (and personally experienced) how painful life becomes in high-rise societies once they’re fully occupied — especially in Hyderabad and Bangalore.

Long waiting times for lifts. Crowded lobbies during office hours. Frustration that no one warned buyers about this.

That’s what inspired me to create the PLAI (Passenger Lift Adequacy Index) — a simple score that helps homebuyers quickly gauge if a building has enough and fast enough lifts for its height and density.

Inspiration also came from this insightful post by @HydSpeaks — which highlights how many under-construction projects ignore lift planning even in 40–60 floor towers.

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💡 The problem

Most homebuyers never ask:

“Are there enough lifts for all these floors and flats?”

By the time they realize it — years later — the society is full, lift waiting time is 10+ minutes, and nothing can be changed.

As cities like Hyderabad, Bangalore, and Pune move toward 40–60 storey projects, lift adequacy is not a luxury issue anymore — it’s a daily convenience issue.

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⚙️ The PLAI formula (works well for 30+ floor towers comparison)

To make lift adequacy measurable, I created a simple formula that balances key factors:

Where:

• L = Number of lifts in the building

• C = Capacity of each lift (number of people) (mentioned officially in the lift)

• v = Lift speed in meters per second

• F = Total number of floors

• f = Flats per floor

• What this formula captures

  ✅ Penalizes height linearly (via F)
  Taller buildings naturally need more or faster lifts. The formula applies a direct penalty with F — doubling the number of floors roughly halves your score (if everything else stays constant).

  ✅ Penalizes density moderately (via √f)
  If more flats share the same set of lifts, wait times and crowding go up. But the penalty is moderate (using the square root) — doubling flats per floor doesn’t double the penalty.

  ✅ Rewards speed, size, and number of lifts — with more weight on lift count
  Lift count (L) now has a slight exponent of 1.1, which means every additional lift contributes more than linearly to the score.
  This reflects reality — adding an extra lift often improves experience disproportionately, especially in tall or high-density towers.
  It reduces waiting time, congestion, and crowding far more effectively than just making existing lifts faster or larger.

  ✅ Keeps the formula compact and interpretable
  Each component plays a clear role. The formula balances simplicity with realism — good enough to compare buildings meaningfully, without requiring simulation-level complexity.

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📊 Examples — How PLAI Reflects Real-World Lift Adequacy

These are not hypothetical calculations — they’re based on actual building configurations from modern residential towers across India.

These are not theoretical values — they correspond closely to real building designs across India.

Each example illustrates how PLAI translates physical parameters into an intuitive adequacy score.

• Tower A (32 Floors, 8 flats/floor, 8 lifts, 3 m/s, 12-person capacity) → PLAI = 3.92 → Excellent

  A well-planned high-rise with ample lift capacity and speed, ensuring smooth traffic flow even during peak times.

• Tower B (32 Floors, 5 flats/floor, 4 lifts, 3 m/s, 12-person capacity) → PLAI = 2.31 → Good

  Balanced configuration with reasonable waiting times; performs well for its scale.

• Tower C (31 Floors, 8 flats/floor, 4 lifts, 2.5 m/s, 14-person capacity) → PLAI = 1.83 → Moderate

  Adequate for typical usage, but some delays may occur during high traffic hours.

• Tower D (29 Floors, 5 flats/floor, 3 lifts, 3 m/s, 10-person capacity) → PLAI = 1.55 → Poor

  Under-lifted for the number of residents; noticeable congestion during rush periods.

These examples highlight how the PLAI model dynamically adjusts for both tower height and lift provisioning, giving a realistic sense of user experience across a variety of designs.

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🧩 The Service Lift Reward Function

In many premium buildings, service lifts play an important role in overall experience.
They handle movement for:

• Housekeeping staff

• Pets and bicycles

• Deliveries, maintenance, and logistics

Having multiple service lifts doesn’t just help convenience — it reduces load on passenger lifts.
However, since service lifts are often slower, their contribution shouldn’t overpower the main score.

✅ When to Apply the Reward

You should apply the Service Lift Reward Function only when:

• The building has more than one service lift, and

• The ratio of service lifts to flats per floor is greater than 0.2 (i.e., 1 service lift per 5 or fewer flats).

In such cases, a small 5% reward is added to the PLAI score to reflect improved real-world experience.

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⚙️ Reward Function Formula

This ensures that:

• Projects with genuinely supportive service lift infrastructure get a small bump

• Those with none or one aren’t penalized

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🎯 PLAI Rating Guide

The PLAI score translates into five intuitive rating levels:

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🧭 How to use this as a home buyer

1. Get these details from the builder’s specs:

   • Total floors (F)

   • Flats per floor (f)

   • Number of lifts (L)

   • Lift capacity (C, usually 8–14 persons)

   • Lift speed (v, typically 1.5–3.5 m/s)

2. Plug them into the formula or this Google Sheets formula:

    =(POWER(C2,1.1)*E2*D2)/(A2*SQRT(B2))
   

   Compare the PLAI score with the rating guide above.
   If your building’s score is below 1.7 → ask tough questions before booking!

3. Rating Assignment:

    =IF(F2>=3.2,"Excellent",
     IF(F2>=2.1,"Good",
      IF(F2>=1.7,"Moderate",
       IF(F2>=1.3,"Poor","Very Poor"))))
   

   (Where F2 contains the computed PLAI value)

4. if you want to add a service lift reward function :

    =IF(AND(G2>1, G2/B2>0.2), F2*1.05, F2)
   

   (Where G2 contains the number of service lifts, B2 contains total flats per floor)

5. You can then apply the same PLAI rating system to the resulting PLAI_final.

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🏗️ What PLAI doesn’t cover (yet)

PLAI is designed to give a practical first-level indication, not an engineering-grade simulation.
Some real-world factors it doesn’t model yet:

• Actual floor height (affects travel time slightly).

• Flat size & population density (large 4BHKs vs 1BHKs).

• Zoned or express lifts that serve only a subset of floors.

• Reward function for shared lobbies

Still, for under-construction projects or early evaluation, PLAI gives a much better comparative view than just “number of lifts”.

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💡 Why this matters

In Indian metros, developers often prioritize amenities or facade over vertical mobility efficiency.
But as towers rise to 40–60 floors, lift adequacy directly impacts your quality of life — from morning rush hours to late-night returns.

A well-designed lift system is not just convenience — it’s core infrastructure.

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🧩 Final thoughts

The Pankaj Lift Adequacy Index (PLAI) is a simple attempt to bring rational thinking into high-rise evaluation.
It encourages buyers and builders alike to quantify lift adequacy, not leave it to guesswork.

Next time you visit a project brochure or marketing office, just ask:

“What’s your PLAI score?” 😄

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