Why Car Pool Lanes Make Everybody Worse Off

The fact that there are still car pool lanes in many major cities (also called HOV (High Occupancy Vehicle) lanes is a testament to the durability of government programs, even when they make no logical sense and make everyone worse off in net balance.

For those who are not familiar with car pool lanes, they are the left most lane of a highway or freeway which are reserved for vehicles with 2 or more passengers. They were designed to “reward” people who travel with friends, family and colleagues and to serve as an incentive for them to pair up for car trips, the theory being, “Hey, if you travel with someone instead of each of you taking your own cars, both of you will get to the destination faster.”

This is one of those times where something sounds fantastic in theory but when you actually think logically about it and put pencil to paper, you don’t need to have a PhD in mathematics to realize that almost everyone is worse off because there are car pool lanes.

Let’s take a look.

Assume for this example that a given highway has 5 lanes in total, and that the left lane has been designated a car pool lane. Now, from my personal experience in Los Angeles, less than 10% of the total cars on the road at a given time, have 2 or more people in them. So simple math leads one to the conclusion that 90% of the cars are crammed into 4 lanes instead of 5 lines, which is a 20% reduction in highway space. Which means that during rush hour when the roadways are very full and traffic moves slowly, we can estimate that the total trip time for someone not in the car pool lane will be approximately 12.5% longer than it otherwise would be in there were the full 5 lanes available. Here’s the math:

Option A with carpool lane: 90 cars in 4 lanes = 22.5 cars per lane

Option B with NO carpool lane: 100 cars in 5 lanes = 20.0 cars per lane.

So the regular lanes in Option A are 12.5% more crowded than they would be in Option B.

True, the 10% of cars in the car pool lane will travel much faster than the 90% of cars in the regular lanes, there will only be 10 cars per lane there, which is a 50% reduction from Option A, which is quite considerable for the people traveling together.

So the net balance is that 10% of the cars will travel twice as fast while 90% of the cars will travel 12.5% slower, and here’s the math for that:

10% of the cars x 2 = .20

90% of the cars x .875 = .7875

So on net balance the average time difference is .7875 + .20 = 0.9875, which is less than one and this means that on the whole, on average, everyone is 1.25% worse off with car pool lanes than they would be without them.

Now, it must be said at this time that if the existence of car pool lanes did actually incentive people to travel together who, in the absence of those lanes would otherwise travel alone, 1 person per car, then the argument could be made that there will be fewer cars on the road and that less traffic decreases travel times for everyone across the board. And this would be true IF, and only if, the existence of the car pool lanes really does incentive people to travel together.

But do they?

It’s hard to say for sure just by doing a “thought experiment,” but anecdotally, I can say with a straight face that I don’t know, and have never to my knowledge ever met, a person who is motivated by car pool lanes to pair up with another person simply in order to take advantage of the extra speed of car pool lanes. If you or someone you know is motivated to do so, please post this fact in the comments and if I hear from enough people that I’m wrong about my assertion, I will gladly revise my opinion on this subject.

If it’s true that car pool lanes don’t motivate a single person to adopt car sharing behaviors, then it is also true that there are the same number of cars on the road as otherwise would be in the absence of car pool lanes, and therefore society as a whole is spending more time in traffic than it otherwise would spend in the absence of such lanes.

True, some people at some times benefit from the existence of car pool lanes. 10% of the people at a given time, get to where they are going faster than otherwise. But these people are not always in the car pool lane and there are times that people can and time when people can’t travel in the car pool lane. So the same people will be benefited some times and disadvantaged other times, depending on the ratio of times they travel with friends to the times they travel alone.

Without belaboring the point, let’s summarize the thesis of this argument as follows: car pool lanes only make sense for a society if they incentivize enough people to travel with companions instead of driving alone. If they don’t incentivize anyone to do this, they make no sense and should be abolished. A well constructed survey of drivers in a given city could probably determine the answer to this puzzle quickly and conclusively.

Father of Five, Husband of One, Slayer of Dragons.