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How many miles of road are there in the US?

estimation estimation market sizing guess-estimates Guesstimate Market sizing
New answer on Jun 29, 2020
2 Answers
6.7 k Views
PK asked on Mar 13, 2020
Director of Product at PayPal. Based in SF. Worked at Twitter, Yelp, Salesforce, Houzz in the past.

Estimate the number of miles of roads in the US?

Clarifying questions:

Are we talking about streets in the city or freeways or both?

Assuming it is both city streets and freeway

Assuming this is for the continental US and not Alaska and Hawaii as well.


Total road miles in the US: City Streets + Freeway - (a)

City Streets - Urban City Streets + Rural City Streets - (b)

Thus, Total road miles in the US: Urban City Streets + Rural City Streets + Freeway length. - (c)

The approach I will take is: Estimates of the miles total city in (b) and then estimate freeway length.

Total Area in the US: Length of US x Width of US

Width of US: 3000 miles (it takes 6 hours to fly across coasts)

Length of US: 1500 miles (take ~3 hours to fly from Seattle to San Diego)

Total Square miles in the US: 3000x1500 → 4.5M sq miles

Based on my travels across the US, I have seen 40% of the US as empty and unpopulated. So I am assuming roads are only int the remaining 60% populated parts of the US.

Square miles of area in the US that is populated → 0.6 * 4.5M sq miles ~ 2.7Msq miles of land area

Assuming, 20% of US city streets are in dense urban areas and 80% are not in very dense cities or rural cities

US City Streets cover → 0.2 *2.7M sq miles of US ~ 0.7M square miles

US Rural Streets cover → 0.8 *2.7M sq miles of US ~2M sq miles

Calculating how many miles of roads are there in the city

From my experience in a dense city like SF, I have seen about 10 blocks per mile and every block has a street running through it. So we can essentially imagine a square mile of city with 10 blocks across in length and 10 blocks across in width. So a square mile has 10 roads running in parallel across length and 10 miles across width, thus, it has 20 miles of road. SF is an extremely dense city so it is not a good representation of all the cities in the US and thus I will assume average major cities have 10 miles of road per square miles.

Assuming 1 sq mile of dense city has 10 miles of road

Thus, 0.7M sq miles will have → 7M mikes of road.

From my experience rural cities have almost 1/4th road density as a city. As a result, I will assume 1sq mile of rural city will have 2.5 miles of road.

Thus 2M sq mile of rural area will gave 5M miles of road …

Thus total city + rural road ~12M miles of road

The above number seems too high, given that I have not accounted for freeways yet. Any suggestions on where I went wrong or what a better strategy would be? May be some of my assumptions are wrong? Also, how do I estimate the number of miles of freeways in the US?


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


I agree with the overall approach, and it´s very detailed.

I agree the numbers end up being a bit high, but this would probably mean that some of the assumptions are overstated.

In any case, what the interviewer looks into here is the methodology, and this one is solid.

Furthemore, this problem is far too complex for an MBB interview.

Well done in any case!



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Anonymous replied on Jun 29, 2020


I would suggest that you should present your own approach and I would be happy to review.

Meanwhile please see below my approach to segmentation in market sizing as well as examples of solved cases:

-Demographics (Age, education, income, family size, race, gender, occupation, nationality)
-Behavioral (Purchasing behavior, customer journey stage, occasion & timing,
customer loyalty & interest, risk tolerance, user status)
-Psychographic (Lifestyle, personality traits, values, opinions, interests of consumers)
-Geographic (Geographical boundaries)

-Company characteristics (Industry, company size, number of employees)
-Geography (Geographical boundaries)
-Purchasing Approach (Occasion & timing, customer capabilities, nature of existing relationship)
-Personal Characteristics (Loyalty, risk attitude, user status)

-Demographics (Type of agency, size of budget, the amount of autonomy)
-Geographic (Geographical boundaries)
-Government Tier (Federal , State, Local, Quasi-governmental, International)
-Bid type (Closed, Open)

But sometimes you don’t need to segmentation. Here is an example of case that could be solved with high level top down approach - estimate the size of credit card market in the US:

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Clara gave the best answer


Content Creator
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut
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