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Estimate The average number of cars passing through brooklyn bridge ? (Per Day )



The question asks for the number of cars passing through a certain day. It provides the following assumptions:

Length of the bridge= 10 km

Car length = 3 m

Spaces between cars = 2 m

Given this, I would assume that the upper limit for the number of cars at any moment will be 10 km / (5m).

How would I take into account the replacmenet concept ? so how can I actually calculate the rate at which the cars enter the bridge (per hour).

Thank you.

Vlad replied on 03/06/2018
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School


You should use the following framework:

Capacity / Throughput / Utilization


1) Capacity - it's the number of lanes, 2 different directions and several levels of the bridge (don't remember how exactly it works on Brooklyn)

2) Throughput - the number of cars entering the bridge per hour. You can calculate it by dividing the total number of cars on the lane (that you've already calculated) by the time it takes to cross the bridge (you can calculate it using the speed. E.g. if the speed is 60 km /hr, length is 10 km, ->it takes 10 min to cross the bridge or 0,167 hr)

3)Utilization - % capacity used at any given hour

Depending on the granularity you need, you can segment into peak / off-peak speed or segment into several groups depending on the time of the day (or day of the week) and calculate the weighted average



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