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How many cars across a local bridge (like Golden Bridge) a hour/day?


Dear All,

I found an interesting estimation case as in the title. Any thoughts/stragegies to solve it?

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Anonymous A replied on 09/18/2017

I'd look at the population surrounding the bridge, e.g. 2 cities from each side of the bridge

then * % adult * % with drivers license * % with car * % travels to work * % travel to work through this bridge * 2 as way/back * 5 days a week = a total car number per week / 7 = avg per day

You can extrapolate this number to add another 10-20% to account for business trucks, tourists and other visitors.

I don't think this question is constrained by the 'supply' of the bridge, as the cars that want to drive through it will be able to do so. UNLESS it is specifically specified that there are traffic jams there.

Vlad replied on 09/18/2017
McKinsey / Accenture / More than 300 real MBB cases / Collected all Big 3 offers / Harvard Business School


Your question is a bit unclear ("a hour/day?").

Let's say you mean the number of cars on the bridge during the Peak Hour.

  1. First of all, make an assumption on how long does it take to cross the Golden Gate bridge and what is the average speed in the peak hour.
  2. Calculate the bridge length with the basic distance formula
  3. Total number of cars = Lenth of a bridge / (Length of a car + assumed space between the cars) * number of lanes in each direction * two directions

If you need an average number of cars on the bridge during the day - calculate both peak and off-peak hours and find the weighted average.

If you mean the average number of cars crossing the bridge per hour - make an assumption about the number of cars entering/exiting the bridge per minute and multiply by the 2 directions, number of lanes, and 60 min. Similarly, calculate separately peak and off-peak and then find the weighted average

Good luck!