Car Corner
How Many Cars Do We Need?

June 1, 2018
By Scott Lewis

This is not an article about how many cars I "think" I need (as many as I can care for without hiring someone to do that for me). I am talking about how many cars does the country, or even the world need.

If you will recall, in my article on autonomous cars I eventually got to the point that the biggest problem with autonomous cars was that we won't need that many cars to provide transportation for everyone.

This month I would like to explore that idea further. Elon Musk, if you are reading this contact me and we can iron out the details on how to make this work. I am confident that we can seriously reduce the number of vehicles in this country, and with your electric plans... we could do a lot to slow down Global Warming.

On to the numbers. I will only use estimates for this country. However, there is no reason this could not scale to all countries with an automotive infrastructure.

There were 268,799,080 (give or take 3 or 4) registered highway vehicles in the United States as of 2016. Source.

We have 327,831,452 people in the U.S. (plus a few as you take the time to read this; it went up by 3 just writing this sentence). Source.

To put those numbers to use, we need some idea of how much those 268.8 million cars are actually being used. The average car in the U.S. is parked for 95% of the time. This comes from a number of sources, but is well summed up here.

Let's assume for a moment that these 3 numbers are completely accurate. For the purposes of this article there is no reason to doubt them (remember, I said this would scale up).

Let's look at this as a giant average. We have 327+ million people requiring the need of 268+ million vehicles. Technically, that means each person only needs 80% of a car. I know, that's crazy... but not if we are talking about sharing cars. Let's plug in the amount of time a car is in use (the reverse of how much it is parked). Each car is in use for only 5% (on average).

At the extreme of people's needs (as a whole), with no regard for excess use... each person only needs 4% of a car. Yea, that is how little a car is actually needed.

That number does not work in reality.

Rush Hour

We need to look at rush hour traffic. A large percentage of people in this country drive during the hours of 6–10am and 4–8pm (source). The average commute in the US is 25.4 minutes (source). The average length of a commute is 12.6 miles (source).

I tried to find traffic information to see how much more cars are travelling during rush hour than not. That is hard to come by. So I will do what any good blogger would do... make something up.

Let's say during those "rush hours" that 50% of the 327.7 million people need to be moved an average of 12.6 miles, for 25.4 minutes. To have enough automotive coverage for that we need X cars running during those peak hours.

Let's solve for X.

We will round up the time to 30 minutes. This makes it possible for 1 car can make 8 trips during the 4 hours of peak traffic. That means 1 car should be able to provide transportation for 8 people (on average). We divide 164 million (rounding up from 50% of 327.7) by 8 and we should be able to transport everyone to and from work with 20.5 million cars. Let's round up again... let's round up a lot. Let's say we need 25 Million cars to provide transportation for 164 million people during the peak travel times across this country.

During non-peak times many of those cars would not be needed. If true, we really don't need more than 25 million cars (give or take 12 or 13 cars), to provide transportation to the entire country during all hours of the day. With over 4 million extra cars, we easily cover down time for maintenance, refueling (recharging), etc.

That is less than 10% the number of cars we currently have registered in this country. WOW!

How will this translate into how many cars will we need each year? That is impossible to determine. I suppose we could try and look at the life expectancy of taxis, because if we don't own cars and just use them, all cars are taxis. Regardless, in 2017 we had 17,241,387 car and light truck sales in the United States (source). We certainly don't need to replace 2/3 of all cars each year (17 million of 25 million in use).

Back to emissions. Having less than 10% of the number of cars does not reduce emissions by 90%. Each car is going to be travelling about 8 times more than a normal car was before. This is close to even. But what if all these cars are electric? Yes, I am talking to you, Elon. Granted, that does not completely remove emissions, it just transfers where the emission are generated. But if the recharging stations are solar powered... well that's interesting.

Since we are talking autonomous shared vehicles, considered the massive efficiency gains if people were willing to car pool. How hard would it be to map the most efficient way to transport 4 people at a time to work? How much does that reduce our needs further?


We really don't need that many cars in this country. We just need to share autonomous vehicles. If that can be done at a cost of less than owning a car... I am in.

What are we wafting for? Elon, give me a call. I'll gladly sit down with you and we can hash this plan out in more detail.

Granted, I still want my 68 Camaro for fun on the weekends.