Ugh... LA traffic
06.19.2020 - Today's market sizing exercise
Hello Case Dojo,
LA is known for its horrible traffic. Let’s try and guess how much the traffic signals have to do with that reputation. Good luck and have fun!
Reminders
Spell out your thinking process, state your assumptions, and evaluate your final answer. There are many valid approaches to each problem.
No calculators are allowed, so make the math easy for yourself.
Try to come to an answer within 3-4 minutes at the longest (here’s a timer).
Today’s Question
How many traffic lights are there in Los Angeles?
Our sample answer
How we broke things down
Let's arrive at the number by multiplying the number of intersections there are by the number of lights per intersection.
There are bigger intersections, which will have more number of lights per intersection, and smaller intersections, that have fewer lights per intersection.
Now we need the number of intersections, both big and small. We can estimate these figures based on each neighborhood and then the number of big and small intersections per neighborhood. We are only counting small intersections with traffic lights.
We can estimate the size of each neighborhood based on the population of LA.
Assumptions we made
LA population = 4M.
# of people in each LA neighborhood = 20K.
# of big intersections per neighborhood = 10 (let's say there are 2 main roads per neighborhood, and each main road has 2 intersections with highway exits/entrances, 3 intersections with local roads).
# of small intersections per neighborhood = 25 (from experience driving in the US, we generally encounter 2-3 smaller intersections with traffic lights every big intersection).
# of lights at big intersection = 8 (there are 4 roadways, each roadway sees 2 traffic lights).
# of lights at small intersection = 4 (4 roadways with 1 traffic light each).
Our evaluation
We arrived at 36K traffic lights in LA. This might be an overestimate because (1) the number of small intersections with traffic lights per neighborhood might be smaller than our figure because there might be stop signs or roundabouts that replace traffic lights.
Other potential approaches we like
Segment intersections into lights, roundabouts and stop signs.
Estimate the number of buildings in LA, and the number of buildings per intersection.
Actual answer
There are 4.5K intersections with traffic signals in LA, but no data on the actual number of lights themselves. We’re probably pretty close.
Extras
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🤠 Fun Fact
In 1928, Charles Adler Jr invented traffic lights that were activated by drivers honking, which were quickly abandoned when residents complained about the excessive honking noise.
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