If that is true, and the marginal car does not much change the traffic situation, why isn’t there boundless demand for the road with slightly worse traffic, increasing congestion now?
Other people have gestured towards explanations that involve changing the timing or length of trips, but let me make an analogy that I think makes sense, but abstracts those things away.
When current is going through a diode, the marginal increment of current changes the voltage so little that we model it as constant-voltage for many purposes. Despite that, the change must be nonzero, or the feedback mechanism wouldn’t work at all. It’s just so small we can often ignore it.
One might similarly imagine that an enormous increase in traffic volume creates a tiny increase in congestion, or vice versa that a tiny increase in congestion discourages an enormous amount of traffic. Then one could say that there is more or less unlimited demand for travel at approximately the current level of congestion—the freeway is a constant-congestion device much as a diode is a constant-voltage device.
(The analogy breaks down at a certain point—if you keep adding cars to the freeway you will eventually get congestion collapse, and the flow of cars per unit time will be reduced rather than increased; whereas if you keep adding voltage to a diode you will rapidly set your diode on fire. I suppose that does reduce the flow of current.)
Beyond the analogy, I wonder what your question is really getting at—it sounds like a general argument that looks at the current equilibrium of congestion vs trips, and asks why the equilibrium isn’t higher, without specific reference to what the current level is. Obviously demand isn’t truly boundless. At some point people must decide the traffic is too bad and stay home. I am reluctant to take a trip that Google Maps colors red, which can mean an estimated travel time more than twice the traffic-free time.
Other people have gestured towards explanations that involve changing the timing or length of trips, but let me make an analogy that I think makes sense, but abstracts those things away.
When current is going through a diode, the marginal increment of current changes the voltage so little that we model it as constant-voltage for many purposes. Despite that, the change must be nonzero, or the feedback mechanism wouldn’t work at all. It’s just so small we can often ignore it.
One might similarly imagine that an enormous increase in traffic volume creates a tiny increase in congestion, or vice versa that a tiny increase in congestion discourages an enormous amount of traffic. Then one could say that there is more or less unlimited demand for travel at approximately the current level of congestion—the freeway is a constant-congestion device much as a diode is a constant-voltage device.
(The analogy breaks down at a certain point—if you keep adding cars to the freeway you will eventually get congestion collapse, and the flow of cars per unit time will be reduced rather than increased; whereas if you keep adding voltage to a diode you will rapidly set your diode on fire. I suppose that does reduce the flow of current.)
Beyond the analogy, I wonder what your question is really getting at—it sounds like a general argument that looks at the current equilibrium of congestion vs trips, and asks why the equilibrium isn’t higher, without specific reference to what the current level is. Obviously demand isn’t truly boundless. At some point people must decide the traffic is too bad and stay home. I am reluctant to take a trip that Google Maps colors red, which can mean an estimated travel time more than twice the traffic-free time.