Author Archive | Brian Davis

A Primer on Trip Generation

As a key factor in determining rates for Portland’s proposed street utility fee, the Institute of Transportation Engineers’ (ITE, henceforth) Trip Generation Manual has gotten a lot of love lately among local transportation wonks. It is worthwhile, then, to take a quick trip through the weeds of the manual to better understand where the opportunities and complications lie when it comes to using this data as the backbone of our fee structure.

First, a bit of context. The art/science/guesswork of predicting the trip generation of various land uses is the first of four steps undertaken in transportation forecasting. Along with the ensuing three steps—determining where, generally, the trips will originate and end; choosing which mode they will utilize; and identifying the time, route choice, and other properties of the individual trips—the goal is to understand the future needs of the transportation system based on current land use and development patterns. Because most jurisdictions have a concurrency requirement—a stipulation that roads and intersections must have adequate capacity to accommodate new demand concurrent with a proposed development—trip generation is of particular interest to folks in my line of work so that we might identify what developers must do to meet this requirement, blissfully ignoring any notion of induced demand.

To this end, ITE has been aggregating and disseminating trip generation data since the first edition of the manual was published in 1976 (the current edition is the ninth). The context manifests in the data in myriad ways. For any of the 172 land uses listed in the manual, the robustness of the dataset is likely a function of both how often that particular land use arises, and how much NIMBY-ism it’s likely to inspire. The well-known suburban bent of the data owes to the fact that most development over the last 40 years has occurred in the suburbs or exurbs, so this is where the vast majority of studies have been conducted.

The trips described by the manual are one-way trips, so what one might colloquially describe as “a trip to the grocery store” is actually two trips: the trip from home to the store, and the return trip home. This is important for analysis purposes—the “trip to the grocery store” will indeed traverse an intersection along the way twice—but results in quantities that are twice as high as what one might intuit. This means that in a closed system each trip is double counted, as both the home and the grocery store would be credited with generating both an inbound and an outbound trip in this example.

The manual provides two general mechanisms for determining the trip generation of a given land use. The first is a mathematical function derived through what’s called regression analysis, which attempts to fit the cleanest possible curve to a set of disparate data points. The second is the trip rate, often expressed as a number of trips per thousand square feet. But it’s important to recognize that square footage is often not the best (or even a viable) independent variable for predicting trip generation. For example, student enrollment is a much better predictor of trip generation for schools, employee count is a better predictor for offices, and the number of ‘fueling positions’ is a better predictor for gas stations.

Interestingly, there’s another predictor for trips generated by a gas station that works better than floor area: the amount of traffic using the street that it’s located upon. That’s because gas stations generate a large number of pass-by trips, which are trips that are ultimately headed to another destination (this destination is credited with generating the primary trip) but stop at a business located directly along the way. A similar type of trip—a diverted trip—is also a trip ultimately headed elsewhere, but in this case the pit stop entails a small amount of out-of-direction travel. There are also internal capture trips, which describe trips that take place entirely on roads and facilities located within a mixed use development. Note the suburban bias there; in the city, this would likely take the form of a person parking once and visiting several locations on foot, using the public streets.

And here we have arrived at the biggest failing of the Trip Generation Manual with regard to our purposes: The manual implicitly considers only vehicular trips. Assuming that only a nominal number of trips are non-automotive might work for the ‘burbs, but this often causes the stated trip rates to be wildly inaccurate in the city. Recent work by Professor Kelly Clifton’s research group at Portland State University confirms what we might have suspected: The more “urbany” a built environment, the more inaccurate the assumption that all trips are automotive is likely to be.

Thus, there is a need to distinguish between the vehicular trips quantified by the ITE manual and what are generally called person trips, which include all trips regardless of mode. Fortunately, as Clifton verifies, the latter seems to be relatively consistent regardless of the built environment. So perhaps by considering only vehicular trips, but doing so primarily in auto-centric locations, the manual has inadvertently provided a good proxy for estimating the differences in person trips generated from one land use to the next. There are exceptions, of course—the manual will understate the person trips generated by a school compared to other land uses, for example, due to the prevalence of buses in travel to and from schools. But it seems that basing a potential street fee on person trip rates inferred from Trip Generation Manual data is defensible and keeps with the spirit of the residential fee in being mode-independent. Basing the fee on vehicular trips, by contrast, would be far more complicated to implement and would leave unsolved many of the issues with the gas tax that Chris Smith wrote about last week.

The manual offers a lot of utility with regard to predicting trip generation, but really it’s just one piece of a puzzle that fits together differently from one land use to the next, and one business to the next. To accurately model the trip generation of a particular business requires a heck of a lot more than the published trip rate, which does not consider countless predictors and is often derived from a small sample size. While using these rates as the basis of the street fee would hardly be the first or most egregious misuse of the data, it seems inevitable that it will result in some businesses substantially overpaying and others substantially underpaying. As luck would have it, that seems to fit with the spirit of this fee quite well.

In Support of a Street Improvement Fee

On Thursday, I’ll be joining what I hope will be a large group of transportation enthusiasts and activists in attending PBOT’s Our Streets Town Hall. Motivated by a series of missed opportunities that have made our 2030 bicycle plan look more like a naïve aspiration than a realistic, achievable goal, and appalled by a recent spate of pedestrian deaths, I’ll offer this argument in support of the street fee.

Winston Churchill once described democracy as “the worst form of government, except for all those other forms that have been tried.” Similarly, a per-household fee may be the worst way of funding our transportation priorities except for all of the other ways that we’ve tried. I say this mindful that I’m fortunate enough to be able to pay the fee without it being too burdensome. For many Portlanders, this fee will hurt, and I hope we can find a way to soften the blow to them while preserving the idea that we all have ‘skin in the game.’ I also would have preferred to see us first take the step of charging fair market rates to those who store their private belongings on our streets by reforming parking throughout the city.  But it is defensible, I suppose, to ask all Portlanders to contribute something before asking those who demand more to contribute more, so long as it’s certain that the latter step will follow.

There’s no doubt that implementing this fee constitutes an improvement to our current funding system. What we’re trying to do at present—fund a multi-modal transportation system with revenues generated largely by motor vehicle travel—is equivalent to trying to fund a methadone clinic with a tax on heroin. It’s a Catch-22 where our ability to provide a solution depends upon the continuing severity of the problem. This new fee is an opportunity to reshape that vicious circle. As such, I expect to see it immediately and drastically change our funding priorities, placing much less emphasis on preserving access and capacity for motor vehicles, and much more on projects that focus on safety, particularly for the most vulnerable road users.

Make no mistake: With regard to demonstrating a commitment to active transportation, we are stagnating. We are stagnating. We have no bike sharing program, nor any concrete plans to deliver one nearly three years after Council voted to do so. And as I write, we are squandering a chance to improve bicycle access on 28th Avenue—a key component of the 2030 bicycle plan. It joins too long a list of recent missed opportunities that includes SW 12th Avenue, NE Holladay Street, and the NW Park Blocks, to name just a few. The news of plans to improve crosswalks along some of our most treacherous roads is welcome, but it’s a modest step. Portland’s walking and bicycling networks remain frustratingly—and often dangerously—incomplete.

I support this new revenue stream because it presents our best opportunity yet to end the stagnation. However the name that seems to have taken hold—“street maintenance fee”—misses the point. The goal here must be to improve our streets. The name of the fee should reflect that. I understand that the finances around street maintenance appear daunting at this moment. But if we were to invest in making our streets excellent public spaces—by holding safety paramount; by prioritizing walking, bicycling, and transit in practice as well as we preach it; and by recognizing that our streets are, as Jane Jacobs so eloquently stated, the setting of an intricate ballet that “never repeats itself from place to place, and in any one place is always replete with new improvisations”—I’d bet that those numbers would start to look a lot more manageable in a hurry.

In fact, I’d bet twelve bucks a month on it.

Shedding Some Light on “Be Seen, Be Safe”

Along with the shortening of the days and the return of the rain, it appears that the parade of retro-reflectivity brought about by campaigns such as Tri-Met’s “Be Seen Be Safe” is becoming an autumn tradition in these parts. The award-winning initiative, which encourages people walking and riding to dress for maximum visibility, probably sounds great to people who see their city primarily from behind a windshield—it would certainly simplify the driving task if everything you weren’t supposed to drive into started glowing and blinking. But for those of us who rely on some combination of walking, biking, and Tri-Met’s ever-diminishing service to move about town, there’s a patronizing naiveté in the implication that all of our anxious moments would abate if only we’d liven up our dour wardrobes with a few shades of traffic cone.

Perhaps a story can illuminate (ahem) my grievances: One recent evening, I find myself in a bit of an adventurous mood as I’m heading south through downtown, so I decide to take the “bicycle facility” on SW Broadway to enjoy the sights and sounds of one of my favorite streets. Ever the good soldier, my ride is fully loaded with front and rear dynamo lights and I’m sporting a hi-viz jacket with retro-reflective strips sewn into every seam. Alas, not more than a few pedal strokes onto Broadway, I notice that the car next to me is creeping closer. Looking over, I see a driver focused laser-like on the smartphone on her lap, and I brake just in time to place myself behind her as she drifts fully into the bike lane. Just as I’m getting back up to speed (12 mph FTW!), a car door swings into the lane in front of me and I have to break hard again. The surprised driver mutters something to me about slowing down as he exits his vehicle. There are a couple of other tense moments—some aggressive drivers and right-hook near misses. It’s all par for the course on the only continuous “bicycle facility” through downtown in America’s Best Cycling City™.

I can wear all the shiny shit I want, but it won’t make me nearly as bright as a smartphone screen if that’s where a driver’s gaze is fixed. Nor will it bestow the power of backward vision upon anybody who doesn’t look for bicycles before swinging their car door into the bike lane. See, with bike lights, retro-reflective strips, and whatever other accouterments I scrape together, I can control whether I’m visible to the users I’m sharing the road with, but I cannot control whether or not I’m “seen.” That part is up to them.

Being maximally visible when it’s dark is a good idea, but there’s a fine line between offering this sound advice and conferring a disproportionate share of the responsibility for safe travelling upon the street’s most vulnerable users. Aside from a legally-required front white light and rear red light or reflector when riding a bicycle, one needs no “proper gear” to walk or bike, despite the campaign’s implication to the contrary. Legally, however, there is an important burden placed upon motorists through the Basic Speed Rule, which requires that drivers maintain “reasonable and prudent” speeds “having due regard for…weather, visibility, any other conditions then existing.” Thus, during the dark, rainy commutes of the Portland winter, the law actually directs motorists to slow down accordingly. How slow? For starters, any speed where you can’t spot and stop for pedestrians regardless of their attire doesn’t sound “reasonable and prudent” to me.

Of course, there’s no mention of the Basic Speed Rule on the “Be Seen, Be Safe” website. Nor are drivers reminded to make sure their car lights are turned on and properly functioning, though one would presume this is just as important for the two-ton, really fast thing as it is for the 200-lb, 12-mph thing. There’s no appeal for drivers to plaster “reflective stickers or tape” all over their vehicles (though that’d certainly be entertaining to see). There is an admonition against distracted driving worded several different ways, but the title shows that the focus of the campaign is elsewhere, which is perhaps why that message isn’t resonating. That’s a shame—“Look Up, Slow Down” would be a better message that properly places the burden on the most dangerous road users (in addition to using objectively more interesting action verbs).

“Be Seen, Be Safe” is a symptom of an auto-centric worldview where if a pedestrian or bicyclist is unseen by a driver then they must have been unseeable. They must have “come out of nowhere.” While it’s an obvious tacit admission that our law enforcement efforts are inadequate and our facilities are growing obsolete, it does little to protect riders and walkers from the myriad of dangers that result. Until we stop trying to put high-viz vests onto straw men and address the real safety issues, I offer in lieu of “Be Seen, Be Safe” the following bit of more practical advice: Do whatever you can to avoid situations where you rely on a motorist’s sobriety, attentiveness, or lawfulness to ensure your safety. Ride or walk like you’re invisible.

If it fits your sense of style, feel free to dress the part too.

A Walktober Tour of Portland’s Crosswalks

I’m joined in assembling this post by Kirk Paulsen, who took the photos within and contributed many great ideas.

It’s October, or as your local walking advocacy group Oregon Walks has branded it for the last two years, “Walktober.” I agree wholeheartedly with the sentiment—there really isn’t a better time to go for a stroll than right now, at the peak of the spectacular northwestern autumn.

Of course, life in the motor vehicle age means that one cannot walk far in the city without soon needing a path across the vehicular part of the road. Hence, crosswalks. Playing the role of the forgettable sidekick to sidewalks, they’re an underappreciated part of the pedestrian infrastructure—the part of the walking trip that is to merely be tolerated, not enjoyed. In turn, crosswalks have come to be one of the most misunderstood pieces of transportation infrastructure.

None of these things is what a crosswalk is.

None of these things are what a crosswalk is.

In celebration of Walktober, we thought it might be fun and worthwhile to take a tour of Portland’s crosswalks, looking at the relationships between location, treatment, and quality. Click through to be whisked away to the best crosswalk in Portland, where we’ll start.

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Meet the “P Design Vehicle”

It is often said of traffic engineers that we’re an auto-centric bunch. I’m sure you’re aware of the list of sins—designing everything to minimize auto delay during the busiest 15 minutes and all that jazz. But what specific auto, pray tell, is at the centre of our auto-centrism?

That would be what we in the biz call the “P Design Vehicle.” The “P” is a creation of the American Association of State Highway and Transportation Officials. Though it doesn’t actually exist, it’s more important than most cars that do, as it is intended to be the standard passenger vehicle that roads and facilities are designed around. Want to build a drive-through access to your business? It has to accommodate the “P.” Want to include some on-site parking with your 40-unit apartment building (and if not, you’re out of luck!)? You’ve got to design it so the “P” can park. Building an adorable little Shared Court [pdf] to enhance the sense of community in your residential development? The “P” has to be able to comfortably navigate it.

Let’s go below the jump for a closer look.

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