. . . are often touted as the answer to our transit woes. The idea is simple enough: When a transit vehicle approaches an intersection, the light changes to give it priority. Trouble is, there’s very little research to suggest it works and transit advocates such as Steve Munro continue to laud this technology without discussing its very dubious track record.
When you dig into the research you see that some cities who’ve implemented it have shown a roughly 6-10% reduction in travel times, which is not, I’ll admit insignificant. Trouble is, most transit riders are more concerned with wait times rather than total travel time (a point made explicit by the Transportation Research Board) and TSP has little impact on wait times.
The Transportation Research Board’s Transit Signal Priority Handbook is a good place to start learning about Transit Signal Priority. The document is very positive on the technology, but that should be viewed with severe skepticism. Of the 32 systems case studies, statistics are only offered for 7. Those seven claim a reduction in travel times, but their methods of evaluation are not reported.
This is an important issue because (as pointed out in another TRB study) most evaluations and studies have been based on computer simulations, rather than on hard, empirical data. The few independent studies that use real-world data show that TSP’s impact is inconsistent and negligible. In fact, in Portland, they experienced an increase in travel times on several routes where TSP was implemented.
I’m not going to say TSP doesn’t work, because I don’t know. I won’t mistake lack of evidence of worth for evidence of worthlessness. But I will ask why it is that cities around North America are spending tens of millions of dollars on a technology that has questionable effectiveness.
Cities throw money at worthless projects all the time, we know that. But wouldn’t it be better, instead, for a few of them to get together, each chip in a little bit of money and hire a legitimately independent and deeply skeptical research team to investigate the technology’s actual worth?
The team would be required not to use computer simulations. They’d have to actually go out and ride, measure and observe the systems in question and report without fear of political interference or reprisal. They’d have to use their own eyes and they’d have to be honest. And if after that we find that TSP is the messiah of transit, then I’ll be all for it. Until then, however, I think we all should be a little more suspicious about TSP’s actual value.
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