Yesterday I put together some maps showing some results culled from google maps on how effective Edmonton Transit is vs driving in your own car. It looked pretty grim for the 'burbs, with average transit times being 20-30min longer than the equivalent trip by car (almost twice as long!). But I didn't really answer whether or not this any impact on actual transit ridership. Intuitively we think it should, but there are lots of other factors as well, such as economics. If you got no money you're still to take the bus (because it is cheaper than driving, slightly) even if it takes you hours.
One way of testing this is to look at the last city census and pull out the transit usage data from that. I goofed off with the census earlier and pulled out transit usage there. As a reminder this is the fraction of the population in a given neighbourhood that use transit as their primary mode of transport (i.e. to get to work and such).
In the following I plot the transit usage against the mean difference in travel times between ETS and Driving for each neighbourhood (in minutes). As you can see for most neighbourhoods taking ETS takes about 10-30 minutes longer than driving. There are many neighbourhoods out in the long tail, though, with transit taking up to 70min longer (i.e. turning what would be a 30min. drive into a 1hr 40min test of patience).
Anyways the big take home is that there is a strong negative correlation between the excess time on transit and transit ridership.
It is also clear from the transit usage map, below, that people who live along the LRT (which is pretty fast) are more likely to use transit than people who are far from the LRT. Which fits with our intuitions, if transit is easy and relatively painless people will take transit.