Every person is unique. Every day is unique. Every trip is unique. As a result, an efficient and equitable transportation system must be diverse, so people can choose the best option for each trip. For example, today you might prefer to walk or bicycle, but tomorrow find it best to use public transit or drive.
There are many aspects of transportation diversity (also called "transportation choice" or "transportation options"). It can include various modes (walking, cycling, ridesharing and public transit), pricing options (such as the ability to rent a vehicle by the hour, or pay for insurance by the mile), services (taxis, carsharing, bike rentals, store delivery, etc.), service quality (such as premium public transportation services, so travelers can choose to pay extra for additional amenities such as on-board refreshments and Wi-Fi), and locations (such as being able to find an affordable home in a transit-oriented neighborhood, not just in an automobile-dependent suburb).
One benefit of transportation diversity is what economists call this Option Value, which refers to the value that consumers place on having an option available, even if they do not currently use it. For example, many people value having public transit service in their community because they might need it in the future. A diverse transportation system is resilient, allowing people to respond efficiently to unexpected change. For example, a multi-modal transportation system (where people can walk, bicycle, ride public transportation as well drive) allows people to maintain mobility even if they are disabled and unable to drive, if fuel prices increase making automobile travel expensive, or if an accident prevents driving on a particular roadway.
The value of transportation diversity is reflected in many ways. Residents of communities with multi-modal transport systems tend to experience less traffic congestion, lower accident rates, spend a smaller portion of their household budget on transportation, exercise more and are less likely to be overweight than residents of automobile-dependent communities.
A recent study by the U.S. Congressional Budget Office, Effects of Gasoline Prices on Driving Behavior and Vehicle Markets measured consumer responses to rising fuel prices. It found that when fuel prices increase motorists reduce traffic speeds, purchase more fuel efficient vehicles, drive less, and if they have access to high quality alternatives, will shift modes. The researchers measured Southern California freeway traffic volumes. They found that vehicle trips declined on freeways that had parallel rail transit service and transit ridership on the corresponding rail systems increased by a commensurate amount, but no such traffic reductions were found on freeways that lack rail transit service. Overall, a 10% increase in fuel prices reduces fuel consumption by 0.6% in the short run and 4% over the long run.
Other studies find similar effects with regard to traffic congestion. Highways with parallel high quality, grade separated public transit service tend to experience less traffic congestion than highways that lack alternatives, because as congestion increases a portion of travelers shift mode, lowering the point of congestion equilibrium. Congestion never disappears (that would require road pricing), but it is significantly lower than what would otherwise occur.
Travelers who lack suitable options are trapped. They are forced into modes and destinations that do not really reflect their preferences. For example, if walking and cycling conditions are poor and public transit service is inferior, commuters will continue to drive even if traffic congestion is terrible and fuel prices surge, but if better options exist they can choose the combination that best meets their needs. This makes consumers better off overall.
This has important implications for all sorts of planning decisions. Over the last century we have developed an excellent roadway system that allows motorists to drive nearly everywhere with reasonable comfort and convenience, except under urban-peak conditions when they face congestion. It now makes sense to diversity our transport system so travelers have viable alternatives, particularly under urban-peak conditions. This will allow individuals to choose the option that best meets their needs for each trip.This is not simply a debate between motorists and non-motorists. Drivers have every reason to support alternative modes because a more diversified transportation system reduces their traffic and parking congestion, accident risk, pollution exposure, and their need to chauffeur non-driving family and friends. It also offers options that they may eventually find useful.
Unfortunately, conventional planning ignores most benefits of transportation diversity. Conventional traffic models evaluate transport system efficiency based primarily on travel speeds, and so they assume that travel shifted from automobile to slower modes (such as walking, cycling and public transit) makes travelers worse off. This assumption is wrong. If consumers shift mode in response to a positive incentive, such as improved travel options or a financial reward such as parking cash out, they must be better off overall, taking into account all of their costs and benefits, or they wouldn't make the shift.
To their credit, many planning professionals and public officials support efforts to improve transportation system diversity much more than is justified by their own economic models. They know intuitively that there are significant benefits to a multi-modal transportation system which are difficult to measure. However, the do this despite rather than with the support of existing transportation models and evaluation tools.
In a typical community, 20-30% of the population has significant constraints on their ability to drive due to age, disability, low income or some other problem. It therefore makes sense that anybody involved in transportation decision-making (planners, city councilors, transportation agency executives) should be required to spend 20-30% of their days without being allowed to drive, so they can experience the transportation system from a non-drivers' perspective. Hopefully, that will help decision-makers understand the value of transportation diversity, and help them identify new ways to create a truly integrated transport system.
For more information see:
Todd Litman (2001), "You Can Get There From Here: Evaluating Transportation Choice," Transportation Research Record 1756, Transportation Research Board, pp. 32-41; at www.vtpi.org/choice.pdf.
K.H. Schaeffer and Elliot Sclar (1980), Access for All, Columbia University Press (New York).