The argument of induced demand goes that way: if more lanes of highway are added, it will initially ease congestion, but more traffic will be generated to take advantage of this new capacity and the highway will reach capacity again in a few years, now with more traffic and without having solved congestion.
Here is what the argument misses: this demande wasn’t induced by the new capacity, the demand was there, but there was no supply. People had trips to make, which they could not because the highways and roads were at capacity, so they did not make these trips.
There is a certain amount of potential maximum demand for different trips in a certain city, and if the supply of roadway is under that level of demand, then inevitably when you add a lane it will immediately fill up and it will have looked like nothing changed. But something changed, more people are using the highway, and that is a good thing, these are trips that people wanted to do and now they can.
What that means is that if you increase the capacity past the level of the demand, and with a good safety margin, then you won’t congest anymore, but you have to reach that point. That is why cities that have very high highway capacity per capita don’t have a lot of congestions compared to cities who don’t (I’d suggest looking it up it’s a very clear correlation).
So yes, more highway capacity does fix traffic, it is just not apparent until the capacity exceeds the supply.
Now I know the argument of public transportation as an alternative to more highway capacity is coming, and to that I say yes, go public transportation. These are not mutually exclusive. I have lived in Paris London and Berlin, cities with great public transportation, and in all these cities people still drive when they can because for a lot of trips driving is simply much faster when it is not congested. Great public transportation is amazing, and my post shouldn’t be understood as an argument against it. Public transportation not only relieves pressure from the roads but also add options for low income users and adds options for everyone. It also allows for denser use of space when necessary.
But highways are not the source of all evil, and a blanket opposition against highways because “induced demand dah” is a mistake, it is a misunderstanding of induced demand. Materialized demand would be a better term.