How many km of roads are there in spain?

estimation Market sizing
New answer on Jan 15, 2020
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Anonymous A asked on Jan 11, 2020

This is a question I got from a consulting firm focused in infrastructure projects. By km of roads it included any kind of road.

What would be your approach to estimating this question?


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Content Creator
replied on Jan 11, 2020
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School


I would split Spain into 3 buckets and allocate % of the area:

  1. Urban areas
  2. Rural areas
  3. National parks / uninhabited areas

1. Urban - you take an average size of the block and find out the number of roads between them (e.g. total Urban length from East to West of 1000km, each block is 1 km, thus 1000 roads from E to W. Same with S and N)

2. Rural - you just assume much lower density than in Urban (e.g. 50x lower)

3. National Parks - will be even lower


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Oleksandr (Alex)
replied on Jan 11, 2020
Very experienced ex-McKinsey consultant with cross-country expertise

Hello there,

I used in my family to play with my own kid (who is 6) asking him similar questions. His brain looks like is being shaped in a right direction, even though he doesn't know precise answers, it's all about the approach.

This case or similar to this one is about how you find the route causes or the main parts, which impact the result. What is important when answering this question is how you think. Even if you have no clue on roads density.

I give you an analogy. How many bulbs one may put on a Christmas tree at max? For answering this question you need to understand:

* Number of tree branches

* Average lenght per branch

* Average size or diameter of the bulb

* And then - use your judgement to understand if the tree will be staying still

In answering your questions, the approach may be similar, although there is more than 1 approach:

1. Top down:

* Size of Spain (in km)

* Judgemental part of country covered by roads (in cities and outside)

* Multiple one by another

2. Bottom up:

* Number of residents & guests in the country (population)

* Part lives in cities and outside

* Time spent per 1 person in the roads

* Average speed of trip

* KM

3. Construction based

* Norm of construction of roads per year since 1900

* Annual growth (linked with: a) car growth, b) infrastructure spending growth or c) productivity growth

* Add some random roads among main hubs and junctions

* KM

4. Evolution-based

* Imagine that the entire territory of the country consists of roads, then - start taking off the number areas, which belong to cities, historical places, parks, mountains, etc. Because in fact - one can try to go through absolute variety of roads (meaning that if there is no road - it doesn't mean one can't go there).

5. Car based

* How many cars are in Spain

* How many KM are driven by car

* How often cars go the same/different direction

* What is the density on the road

* How large part of road had never being driven on (or let's say for the past x years)

* KM

PS. you may find some other x alternatives of answering this question. Pls don't be always simple and straight, show some of the imaginations. Esp in infrastructure projects in Spain!

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Content Creator
replied on Jan 15, 2020
McKinsey | MBA professor for consulting interviews

in order to calculate rural areas - in order to not overcomplicate the case - I would simply add a percentage on the total km of city and highway roads.


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Content Creator
replied on Jan 13, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut


The "academic" approach in this case would be splitting territory in buckets, estimate the km2 per each bucket and estimate the km of roads per bucket.

However, this can get very tricky and too many assumptions if you don´t know the country well (e.g., I wouldn´t be able to calculate the % of urban areas from other european countries accurately).

Hence, I would try to make analogies with a country with which you feel comfy, such as your own. You can estimate the km of roads connecting big, medium and small towns, and then make the analogy to Spain.

Hope it helps!



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Content Creator
replied on Jan 12, 2020
BCG |NASA | SDA Bocconi & Cattolica partner | GMAT expert 780/800 score | 200+ students coached


I would use the approach suggested by Vlad, splitting the country in Urban area, rural areas and national parks/uninhabited areas.
In addition to this,I would consider also the distance between the big cities in order to consider also the highways that can affect significantly the result.


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Vlad gave the best answer


Content Creator
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School
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