The way we quantify how well our roads are (or aren’t) working isn’t something that tends to get a whole lot of play outside of the transportation wonkery, but it has a drastic effect on policies and livability. The most commonly used metrics to describe our system, including the infamous level-of-service metric, are drawn from something called the Highway Capacity Manual. See how the name of the manual doesn’t really imply that it’d be terribly useful for designing safe, welcoming local streets? Most jurisdictions don’t, and that is one of the main reasons why too many urban streets have become de facto highways.
Over the last several years, traffic engineers have increasingly been letting go of their long-held fondness for LOS and other traditional performance metrics, and in many cases are even leading the charge against them. The inadequacy of LOS as a primary measure of performance is perhaps most clear in California, where the state’s all-powerful Environmental Quality Act buttressed the importance of the metric by (ironically) requiring that environmental analyses consider LOS when evaluating the impacts of a project. So perhaps it’s not surprising that California has struck the most major blow to date to LOS, with new guidelines that evaluate projects based not on how much they will increase auto delay but instead on how much vehicular traffic they induce.
It’s hard to overstate how radically that this departs from the status quo. For many jurisdictions, an over-reliance on capacity-based metrics have produced policies that favor anything capable of moving one more car. California’s new standards appear to turn this idea on its head, favoring policies and land uses that create one fewer trip (or one fewer vehicular mile traveled). Thus, it would appear that analyzing a particular idea with California’s VMT-based methodology—whether to widen an intersection approach to include a turning lane, for example—might lead to the opposite conclusion as analyzing it with traditional metrics. Though the turning lane would certainly reduce delays and thus improve LOS, there’s plenty of evidence to suggest that it would also induce new traffic and thus be undesirable (or impermissible, even?) based on the VMT-based metric. That’s huge!
The VMT-based metric is neither perfect nor wholly complete. Success of the methodology relies heavily upon our ability to estimate the number of trips a project may generate which, as I described here, is something of an inexact science. The need to include trip length in these projections serves to widen the gulf between the data that’s needed and the data that’s available. And the state’s guidance [pdf] for utilizing the new methodologies do not appear to significantly improve upon the half-hearted methodologies engineers currently employ to evaluate safety ramifications of a given project. Finally, a scathing white paper [pdf] from UCLA’s School of Public Affairs suggests that the VMT-based methodology may not even be all that great at its purported goal of teasing out the environmental impacts of a project, although I’d hasten to challenge some of the assumptions their analysis is based upon.
Despite its shortcomings, the new VMT-based methodologies represent a big step forward and I’ll be curious to see how they’re applied by colleagues in California. Those of us who favor a multi-modal and safety-oriented approach are regularly stymied by traditional metrics that concern themselves with only capacity and delay, only as they pertain to autos, and only during the busiest 1% of the day. Though it leaves important considerations unaddressed, California’s new methodologies offer a way to overcome these hurdles. Time will tell what effects this will have, but there’s plenty of reason for optimism.
So what does this mean for Portland? That’s a good question. It’s now been two years since the city launched a project to update our performance standards, but sadly this effort seems to have disappeared into the same memory hole as bike share. Keeping with a storyline that’s becoming too familiar, others innovate while Portland waits.2 Comments