This is an interesting one. To be honest, its very unlikely to provide a good estimation if you dont have a good knowledge of the german highway system.

But here's my attempt.

First consider the country dimensions. Let's say it's about 900 kms long and 600 kms wide.

Then consider how far away from each other are highways. Let's say there's a highway every 100 kms. I pick this number because Germany is a densely populated country with an automobile tradition and known for its highways. I would probably pick 150 kms for Spain (lower population density, but modern road infrastructure) and 200 kms for Poland (density similar to Spain, but still building out its highway system). 

So for Germany that would mean 9 highways “horizontally” (each with 600 kms) and 6 “vertically” (each with 900 kms). But since Germany is not a perfect rectangle, 5 vertical would be more appropriate.

So that is: 9*600 + 5 * 900 = 5400 + 4500 = 9900

Now, highways have turns… so they are a bit wider and longer than our estimation. So let's consider an additional 20% for that, taking into consideration that there a long mountain ranges in the whole half south of Germany (meaning more turns)

So 9900 * 1.2 = 11880 kms (you can round this to 10000 * 1.2 = 12000kms)

Just out of curiosity, the real number is 13200. It's not really relevant if it is spot on or not. In this type of case probably being 50% or off (or more) is perfectly fine - the real issue is your logic).

Hope this helps.

Hi Theresa,

If you're able to ask this question in English more of us will be able to help you!

From Google Translate, I can see this is a market sizing question. 

You'll learn a lot more from this by trying it out yourself first! Why don't you post your approach here and we can provide commentary?

How to approach market sizing

It's very simple: Do the approach the is the easiest for you given the question.

Are they asking you to estimate something where you don't even know where to begin from the top (maybe you have 0 clue as to the market size of the industry, the GDP of that country, etc. etc.)? Then do bottom-up!

Alternatively, does it seem impossible to do a realistic from-the-ground-up estimation of something (perhaps it requires just far too many steps and assumptions)? Then do top-down!

Fundamentally, you need to take the approach that just makes the most sense in that circumstance. Quickly think about the key assumptions / numbers required and whether you 1) Know them or 2) Can reasonably estimate them. If you can, go ahead!

An Example

He's a Q&A for a great market sizing question here asking to estimate # of electric charging stations in a city in 10 years:

https://www.preplounge.com/en/consulting-forum/how-would-you-solve-this-market-sizing-question-from-roland-berger-7631

This one could be answered top-down (as I did) by estimating population of the city, # of drivers/ cars, etc. etc.

OR, it could be answered bottom-up by estimating # of stations you see per block (or # of gas/petrol tanks), % increase this might be over time (or # of EV stations that would be needed per gas tank given EV stations take 10 times as long), and # of blocks you'd estimate the city to have.

Take a look here for additional practice! https://www.preplounge.com/en/management-consulting-cases/brain-teaser/intermediate/taxis-in-manhattan-market-sizing-229