Saturday, October 8, 2011

Background on the high-income transit riders

Eric Jaffe at the new Atlantic Cities blog picked up on my last post, and said some really nice things. Between him and a mention on the Streetsblog Network, I got a few useful questions.

1. Eric wonders about Torrington, Connecticut: "Cap'n Transit suggests it forms an outer ring of New York City; if that's the case, the commute should be longer than an hour, since it takes 45 minutes by bus to reach New Haven, which is still an hour and a half from New York on Metro North. Bus riders into Hartford may instead be the source the discrepancy."

There are a few things going on here. First of all, as Tim Evans commented on the Atlantic Cities post, Torrington is the city of 36,383 that lends its name to the Torrington Micropolitan Statistical Area, a census area that basically refers to Litchfield County. That means that we're talking about commuters from all over northwestern Connecticut, including people who live within a few miles of the Metro-North train stations at Danbury, Waterbury and Southeast. The ACS form (PDF) asks, "How did this person usually get to work LAST WEEK? If this person usually used more than one method of transportation during the trip, mark (X) the box of the one used for most of the distance." So if you drove 30 miles of a 61-mile commute, you would count it as a transit commute. Even if the 30 miles of driving took 45 minutes.

But if it takes two and a half hours to get from Waterbury to New York, and the Torrington ╬╝SA is a half hour from the Waterbury train station, including parking and padding, then how does the average commute time only come to 62 minutes? Well, there are probably quite a few people commuting to suburban job centers like Stamford, Hartford and White Plains. It may be people riding the bus that Eric mentions into Hartford, but I'd be surprised if that kind of demand-response service gets much use. If they're middle-class bus commuters to Hartford, they'd probably take the Bonanza, Peter Pan or Greyhound buses. They can also take Metro-North to some of the destinations.

2. In the comments to my own post, Rob Pitingolo asks, "Can you elaborate a bit on the methodology? Did you simply pull these numbers down from the American FactFinder? If so, can you please provide the table ID? Since the 2010 ACS microdata hasn't been released yet, I'm guessing that you used the tabular data, but would really like to confirm that this is the case."

Great question. Some of you have also asked to tweak the analysis in various ways, so let me tell you how I did it, and you can go right ahead and download your own data! First of all, here's my tabulation of the data, so you can pick it apart.

What I did was to download Table B08301 for the overall commute mode choices, B08121 for the earnings data, and B08136 for the aggregate travel time. I combined them into one Excel workbook and cross-referenced them using the Vlookup function. I calculated mean travel time by dividing aggregate travel time by the number of commuters, and I calculated the earnings and time ratios in a similarly straightforward way. I compared the absolute value of the difference in earnings to the margin of error in transit earnings as a check on the statistical significance of the sample.

So knock yourselves out! If you find something interesting, post a link in the comments here. I'm looking forward to seeing what you dig up.

2 comments:

George K said...

I think the person is told to calculate their entire commute, but only list the mode of transportation they used most.

So if a person drives 15 minutes to a rail station and spends 45 minutes on the train, they say that they take a train and spend 60 minutes on their commute.

I'm 99% sure that's how it works.

So the explantion for the short travel time is probably that a lot of people are working in offices in Stamford, Hartford, White Plains and other cities, and maybe they're driving to an area like Waterbury and taking the train in (since fares within Connecticut are fairly reasonable)

Alon said...

George, the ACS asks people to list the mode of transportation by which they traveled the greatest distance.