The Arizona Republic had another of its cheerleading articles on light rail this morning. In it was a chart that, contrary to the intent of the article, summarized exactly why Phoenix light rail is doomed. Below is a chart of the employment density (top chart) and population density (bottom chart) at each stop along the first rail route. Note that this line goes through what passes for the central business district of Phoenix and the oldest parts of town, so it was chosen to run through the highest density areas - all future extensions will likely have lower numbers. Unfortunately, they do not reproduce this chart online so here is a scan:
Take the population density chart. As a benchmark, lets take Boston. The average density for all of the city of Boston is 12,199 people per square mile. Phoenix's light rail line cut through the highest density areas of town has only one stop where density reaches this level, and most stops are less than half this density. And this is against Boston's average, not against the density along its rail routes which are likely much higher than the average.
Rail makes zero sense in a city like Phoenix. All this will do is create a financial black hole into which we shift all of our bus money, so the city will inevitably end up with a worse transportation system, not a better one. Cities that build light rail almost always experience a reduction in total transit use (even the great God of planners Portland) for just this reason - budgets are limited, so since rail costs so much more per passenger, other transit is cut back. But the pictures of the train will look pretty in the visitor's guide.
Postscript: Phoenix's overall average density is around 2,500 per square mile. Assuming that the 12,000 in the chart above is one of the densest areas of Phoenix, this gives a ratio of about 5:1 between peak and average density. This same ratio in Boston would imply peak density areas of 60,000 per square mile. This may be high, but indicates how much higher route densities on Boston rail should be. Oh, and by the way, Boston rail is losing a ton of money.
Other city densities here from 1990. People think of LA as spread out, but LA has a density over three times higher than Phoenix!