Adam Millard-Ball has a nice article on Phantom Trips. in Access Magazine
Traffic lies at the heart of many fears about new urban development. In some cases, cities require developers to scale back housing or retail proposals to alleviate concerns about congestion. In other cases, cities widen roadways, add turn lanes, or lengthen signal cycles to accommodate projected traffic volumes.
In both instances, planners and engineers wield considerable influence through their predictions of the number of vehicle trips that a proposed development will generate. This seemingly mundane process—trip generation analysis—profoundly shapes the physical form and financial feasibility of urban development. Estimates of trip generation help shape the road infrastructure, determine the amount that developers must pay for new roads and greenhouse gas mitigation, and sway local support or opposition to proposed development. Trip generation practices also help determine how much urban space cities dedicate to cars; the viability and character of transit-oriented and infill development; and whether a project proceeds at all.
How do we predict how much more traffic there will be? In the United States, the Institute for Transportation Engineers’ (ITE) Trip Generation Manual, now in its 9th edition, is the standard reference. It provides data on the number of trips generated by 172 different land uses, from “Baby Superstore” to “Cemetery.” Some of the land-use categories are remarkably specific, such as “Batting Cage” or even “Coffee/Donut Shop with Drive-Through Window and No Indoor Seating.”
Given the ubiquitous influence of the Trip Generation Manual on the built environment, it is important to understand the validity of its data and ITE’s recommended practices. Rather than accurately forecasting the impacts of new developments, I show in this article that ITE substantially overestimates trip generation rates. Moreover, I explain why ITE’s core premise, that development always generates new trips, is misleading in many circumstances. Because ITE rates do not fully consider how trips are reshuffled among destinations, they are often inappropriate for evaluating traffic, fiscal, and environmental impacts. In short, we are planning for “phantom trips” that never appear in reality.
This article is adapted from “Phantom Trips: Overestimating the Traffic Impacts of New Development,” originally published in the Journal of Transport and Land Use. [forthcoming 8(1)]
Accessibility, long considered a more robust measure of transportation system success than simple mobility, is moving out of research and into practice, according to panelists on an SSTI webinar.
Accessibility measures the ease by which travelers can reach desired destinations, or “opportunities.” Often, but not always, it is measured in terms of time. As such, it combines both mobility and proximity of land uses, bringing together two directly connected public policy concerns that are often poorly integrated in decision-making.
While accessibility is not a new concept, data limitations have made it difficult to measure. Now it is becoming practice-ready, panelists said.
The webinar, broadcast Dec. 4, featured Andrew Owen of the University of Minnesota’s Accessibility Observatory, Richard Kuzmyak of Renaissance Planning Group, and Kate Sylvester of the Maryland DOT. Slides and a recording are available on the SSTI website.
Owen, who cited commentary in the conservative National Review and libertarian Reason Foundation about the benefit of accessibility measures, has been working with Minnesota DOT and now is developing a pooled fund study to mainstream accessibility measures across the country. Kuzmyak has applied accessibility measures in the Washington, D.C., area, including in a project with Sylvester’s Maryland DOT.
While both efforts aim to make use of accessibility for better transportation and land use decision-making, the approaches are somewhat different.
Owen’s group uses a cumulative opportunities count, generally using jobs as the critical opportunities. They estimate the number of opportunities that can be accessed by car and transit from neighborhoods around the nation within a set time, say 30 minutes. …
“My dear guests, I am Mr. Roarke, your host. Welcome to Autonomy Island.”
Yes, here on Autonomy Island, all of the cars are autonomous. Your adventure will be to ride and drive in a place without fear of a human running you over.
When will an automaker (or collective of automakers, or government, or Google) buy all the cars on an island (and perhaps rent the government), replace them with new autonomous vehicles, and see what happens … to safety, to travel behavior, etc?
This is the kind of real world laboratory experiment that would be highly useful to understand the implications, the unintended side effects, the bugs and so on of robotic cars.
For instance, take the US Virgin Islands. St. Croix has a population of about 50,000 people. If it follows general US patterns, it has about 33,000 light vehicles. For about $1B [Less than the cost of a single NFL stadium] all of the cars could be replaced with autonomous vehicles at about $33,000 each. [This might be a stretch, but that would be a typical mass production cost.]
The advantages of an island are that it is a closed system, it can be fully mapped, no one can drive on or off. The advantages of a real island with real people are the ability to see how these interactions might actually occur in use.
Autonomous vehicles interacting with only autonomous vehicles should be much easier to design than autonomous vehicles in mixed traffic, as the environment is less variable. People, animals, weather, and so on are still potential confounding factors, but should be simpler to manage than a person in a car.
Using detailed travel surveys conducted by the Metropolitan Council of the Minneapolis/Saint Paul region for 1990, 2000-2001, and 2010-2011, this study analyses journey-to- work times, activity allocation and accessibility. The analysis shows a decline in the time people spend outside of their homes as well as the time people spend in travel over the past decade. Although distances per trip are increasing, the willingness to make trips is declining, resulting in fewer kilometers traveled and less time allocated to travel. This study finds accessibility to be a significant factor in commute durations. Accessibility and commute duration have large effects on the amount of time spent at work therefore activity patterns are influenced by transportation and the urban environment.
In 1863, the Metropolitan Railway of what came to be known as the London Underground successfully opened as the world’s first subway. Its high ridership spawned interest in additional links. Entrepreneurs secured funding and then proposed new lines to Parliament for approval, though only a portion were actually approved. While putative rail barons may have conducted some economic analysis, the final decision lay with Parliament, which did not have available modern transportation economic or geographic analysis tools. How good were the decisions that Parliament made in approving Underground Lines? This paper explores the role accessibility played on the decision to approve or reject proposed early London Tube Schemes.
Many planners argue for greater integration of transportation and land use policy. In the US, many argue that separated policy realms contributed to the system of automobility and low density cities that exist, in part because transit investment isn’t able to capitalize real estate benefits. This is different than the historical connections between streetcar companies and real estate development in nascent suburbs. In recent years transport planning, and transit planning in particular, has attempted to reshape the urban landscape through new infrastructure investment. A common refrain is that real estate developers love the “permanence of rail” when it comes to making location decisions about where to build. Another way strong connections between transportation and land use are promoted are through value capture mechanisms for road or transit projects. Overall, the contemporary debates about infrastructure tend to revolve around “how much” change to the built environment will be caused by new investment. This assumes a strong and measurable relationship between transportation and land use. Better questions may be: 1) whether the relationship is strong enough to affect change at all, and 2) are the connections between transportation and land use strengthening or weakening?
A weakened connection between transportation and land use is not a new idea. Gen Giuliano, for one, wrote about it in the 1990s. Marlon Boarnet argued more recently that changes in transportation will be a much bigger deal than changes in density moving forward. In short the argument is that ubiquitous automobility has reduced the onetime spatial advantages due to proximity to a limited number of transit options. At present there are good reasons to improve our understanding of how transportation and land use interact. Broadly speaking, there are two current approaches to transportation. First, there is massive public investment in a limited number of infrastructure projects. Such projects—light rail, commuter rail, streetcars, road expansion, etc.—represent a form of spatial planning where favored locations are gifted desirable infrastructure as amenities, with some expected transportation improvement that is mostly measured in travel time. Second, there are countless private firms working on selling personalized mobility. Taxi companies, tech-taxi companies, private bus companies, commuter shuttle services, vanpools, shared vehicles and others are all competing for passenger travel business. These companies are reacting to existing land use development and taking advantage of existing infrastructure to improve access by personalizing mass transit. Plus existing and new automakers are adapting their cars and business models to current and future consumer preferences and trends, and of course self-driving cars are coming as well.
The public model of large investment in a limited space stands in contrast to the private model of many alternatives working to customize transit to maximize accessibility across regions. The public clearly believes that the transportation and land use connections are strengthening, and the private firms are indifferent or they see a weak connection moving forward, which is why “real time data” is so important to everyone. A weaker transportation and land use connection suggests that spatial planning through infrastructure (see here for an Australian report on this issue, though this applies globally) will be ineffective, which has implications for local land use policy and transportation finance.