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By Calvin Tribby

A friendly reminder to the Utah Transit Authority regarding a news story that appeared in The Tribune on July 11 headlined "SLC tops nation in transit connecting people and job": The Brookings Institution study on job accessibility by transit which came up with the ranking is but one measure of a transit provider.

Since this is a national, metropolitan-based comparison study, there are numerous simplifications at the local level, where the transit service is actually used. The aims of the study are to produce a supply-side-only assessment of the potential for transit to be used for commuting to work. To put the findings of the study — that the Salt Lake metro area is ranked first in the nation for connecting people with jobs — in context, a brief critique of the study is warranted to clarify some assumptions and limitations.

First, the assumptions of the study do not agree with current practice in transportation research. The 90 minute one-way commute time by transit to work overestimates the willingness of commuters to travel to work by transit. Nearly 75.6 percent of commuters using transit in SLC travel for 60 minutes or less, according to an American Community Survey (2006-2009).

Furthermore, the willingness to walk to a transit stop is also overestimated in the study: three quarters of a mile; accepted standards do not exceed a half mile.

Second, the area-based aggregation measures used to calculate jobs and population are arbitrary. For example, the population-weighted geographic center of a census block group was used to calculate the distance to the nearest transit stop, to categorize that population as having access to the transit network or not. This aggregation obscures the physical barriers to the nearest transit stop due to the neighborhood-built environment, such as cul-de-sacs and interstates.

The study also assumes that the closest transit stop will be useful for the entire block-group population, which, given the generous commuting time assumption, allows for many transfers between routes in the system. This is unrealistic, as transit riders seek to minimize transfers, with a substantial decrease in the likelihood of transit use as the number of transfers increases.

Lastly, this study focuses on the weekday, morning commute time (6 a.m. to 9 a.m.) when transit service is the most extensive. Some employment categories assessed in this study — shift work in the services industry, for example — do not adhere to this narrow window of time. Transit service at other times of day may be substantially less or nonexistent.

There are many sources of overestimation of accessibility to employment in this study, among them generous commute-time allowances, the length of assumed walking distances, and peak-hour transit service.

While the above limitations apply to all the metro areas studied, specific data on transit use does exist for comparison between metro areas. One measure of a transit provider's success is the actual split of the mode of commuting to work that the system attracts.

In the Salt Lake metro area, the UTA system attracts only about 3.1 percent. The Brookings hypothetical value is that 64.1 percent of jobs are able to be reached by transit. For comparison, Chicago metro had 11.7 percent of work trips by transit, but only received a hypothetical score of 22.8 percent.

So, is UTA more successful than the Chicago metro area? By the Brookings measure, yes, but by actual transit usage, no.

This highlights the limited applicability of the Brookings report. While national comparisons of transit systems are useful, misinterpretation or overstating the importance of the findings is troublesome. While the findings may be good for UTA publicity, the limitations and design of the study need to be considered when accepting these results.

Celebrations of UTA's rank are premature, and especially management's justification of policy decisions that led to such a ranking, while our actual transit commute mode share is dismal.

Calvin Tribby is in a doctoral program on transportation geography at the University of Utah.