Rising gas prices never had much to do with people increasing their use of public transit. Some of it is simply that there are more options in more places now. Some of it is a change in preferences for where people want to live.
And, yes, there is an economic component. No damn jobs and no damn money encourage people to live where they don't need a car, and to live in places with more rental housing availability. Those generally match up fairly well.
While gas at $4-4.50 might nudge a few people to the park-n-ride, it'd take a much higher price than that for people, given their existing locations which mostly lack decent public transit, to switch modes in any significant number.
At $2.50, people will probably drive a bit more, but the difference between $2.50 and $4 isn't enough to make large numbers of people make significant lifestyle and location changes.
