1. Introduction

Management experts often say that, "you can't manage what you can't measure." What is measured, how it is measured, and how data are presented often affects how problems are defined and solutions evaluated. A particular solution may appear best when measured one way, but undesirable when measured another way.

For example, baseball performance can be evaluated based on batting averages, base hits, runs batted in, and ratio of wins to losses, not to mention various defense statistics that depend on position. Performance statistics can be calculated per at-bat, per inning, per game, per season, or for a total career. A player can be considered outstanding according to one set of statistics but inferior by another.

This is one examples of how different measurement methods can affect how things are evaluated. Often, there is no single method or unit that conveys all the information needed for evaluation. Different measurement units represent different perspectives and highlight different features. Decision-makers may need to consider a variety of different statistics. It is important that people using such information understand the different perspectives and assumption implicit in the units they use.

This chapter discusses different methods used to measure urban transportation, the different perspectives they represent, and how the selection of one or another method tends to affect transportation and land use planning decisions.

2. Traffic, Mobility and Accessibility Perspectives

Transport systems can be evaluated using different techniques that reflect different perspectives about the nature of transportation, the definition of problems and which solutions can be considered best. Three perspectives, referred to as “traffic,” “mobility” and “access,” are described and compared below in terms of how they view users, modes, land use, transport problems and solution, and how they are measured.

Traffic

Traffic refers to vehicle movement. This perspective assumes that “travel” means motor vehicle travel and “trip” means vehicle-trip.

• Users. From this perspective, transportation users are primarily motorists (including drivers, passengers and businesses that rely on commercial deliveries). Non-motorists are considered a relatively small and unimportant minority, since in most communities the majority of households own motor vehicles, most travel is by motor vehicle, and motorists pay the majority of transport taxes.
• Modes. This perspective focuses on automobile travel. It places little value on transit and cycling, since they represent a small portion of vehicle-mileage. It considers walking primarily as a way to connect destinations with vehicle parking facilities, or as a form of recreation, and so devotes minimal transportation funds to nonmotorized facilities.
• Land Use. This perspective considers convenient access to major highways and abundant parking the most important land use factors. The most desirable location for major activity centers is directly off a major highway or arterial, at the urban fringe, in the center of a large lot of unpriced parking. A downtown location is undesirable due to roadway congestion and parking costs.
• Transport Problems and Solutions. This perspective defines transportation problems in terms of costs, barriers and risks to motorists. It favors solutions that increase road and parking capacity, roadway design speeds, vehicle ownership, and minimize the cost of driving. From this perspective, the best way to address the barriers facing non-drivers is to help them become motorists, by making automobile use and taxi service convenient and affordable.

Vehicle traffic is relatively easy to measure. Most jurisdictions have data on motor vehicle registrations, drivers licenses, and vehicle mileage. Performance indicators include traffic volumes, average traffic speeds, roadway Level of Service (LOS), congestion delay, parking supply, vehicle costs and crash rates.

Mobility

Mobility refers to the movement of people or goods. It assumes that “travel” means person or freight travel and “trip” means person or freight-vehicle trip. It assumes that longer trips provide greater value to society than shorter trips, and faster modes are superior to slower modes. It supports an integrated view of the transportation system, with attention to connections between different modes. For example, it recognizes that most transit trips involve at least one walking link, and so walking and transit are complementary travel modes.

• Users. From this perspective, transport users are mainly motorists, since motor vehicles provide the majority of personal-miles and freight transport, but on some corridors there are enough transit users, rideshare passengers and cyclists to justify special consideration. It recognizes that a significant minority of residents use non-automobile modes at least occasionally.
• Modes. This perspective considers motor vehicles most important, but also values transit and ridesharing on congested corridors, and recognizes that walking and cycling may be important in areas such as college towns and resort communities. It supports an integrated view of transportation systems, with attention to connections between modes. It justifies devoting a modest portion of transport funding to transit, HOV and cycling.
• Land Use. From this perspective, convenient highway access and parking is considered most important, but transit and HOV access are also desirable in areas where density and demographics concentrate enough riders. The best location for major activity centers is where there is a combination of convenient roadway access, adequate parking, and transit service, and a central business district can be accommodated by emphasizing transit.
• Transport Problems and Solutions. A mobility perspective favors solutions that increase transport system capacity and speed, including highway improvements, transit improvements, ridesharing, intermodal passenger and shipping facilities, high-speed train and aviation. It tends to give little consideration to walking and cycling except where they provide access to motorized modes, since they represent a small portion of person-miles. From this perspective, the best way to address the barriers facing non-drivers is to improve mobility options, including automobile, taxi, transit and nonmotorized transport modes.

Mobility is measured in person-miles, ton-miles, and travel speeds. Mobility is sometimes measured door-to-door, taking into account each link of a trip, including walking to a parking lot or transit stop. This is relatively difficult to measure because it requires tracking people and goods, rather than just vehicles, including each link and waiting period in each trip (such as walking to a vehicle and waiting for a bus). In recent years transportation engineers have developed standardized methods for calculating pedestrian, cycling and transit Level of Service, just as they do for automobile traffic [IHT, 2000; FDOT, 2002).

Accessibility

The ultimate goal of most transportation is Accessibility (or just access), the ability to reach desired goods, services, activities and destinations (collectively called opportunities). The exception is a small portion of travel in which movement is an end in itself (historic train rides, horseback riding, jogging), but even recreational travel usually has a destination, such as a resort or a camp site. This perspective considers vehicle traffic a subset of mobility, and mobility a subset of accessibility. Accessibility is evaluated based on the time, money, discomfort and risk (the generalized cost) required to reach opportunities. Individuals often think of it as convenience, that is, the ease with which they can reach what they want.

Access can be evaluated at many different geographic scales.

• At a very fine-grained scale, accessibility is affected by the quality of the pedestrian conditions and the clustering of activities within a site, mall, campus or small district. For example, strip commercial development tends to be less accessible than a commercial center because customers, clients and employees can walk between businesses rather than needing to drive to each destination.
• At the neighborhood level, accessibility is affected by the quality of sidewalks and bicycle facilities, street connectivity, geographic density and mix. For example, a more accessible neighborhood will tend to have shops and public services (e.g., schools) within or adjacent to residential areas so some errands can be made by walking, cycling, transit, or short car trips.
• At the regional level, accessibility is affected by street connectivity, transit service, geographic density and mix. A more accessible region will have a network of many roads (rather than just a few major arterials) and efficient transit service that makes it convenient to travel within the region by car or transit.
• Interregional accessibility refers to the quality of highways, air service, bus and train service, and shipping services.

The major perspective are:

• Users. From this perspective, transportation users consist of any person or businesses that wants to reach a good, service, activity or destination. It recognizes that most people use a variety of access options.
• Modes. This perspective considers all access options as being potentially important, including walking, cycling, public transit, telecommunications that substitutes for physical movement, and more accessible land use. It supports an integrated view of transportation and land use systems, with attention to connections among modes and between transport and land use patterns. It values modes according to their ability to meet users’ needs, and does not necessarily favor faster modes over slower modes. It supports the broadest use of transport funding, including mobility management and land use management strategies if they increase accessibility.
• Land Use. From this perspective, land use is as important as mobility in the quality of transportation, and different land use patterns offer different types of accessibility. Land use clustering, mix, network connectivity and pedestrian conditions all affect accessibility, as discussed below. The best location for major activity centers is where there is a combination of convenient roadway access, transit service, and walkability.
• Transport Problems and Solutions. Accessibility-based planning expands the range of transport problems and potential solutions that can be considered. From this perspective, transport problems include any cost, barrier or risk that prevents people from reaching desired opportunities. Solutions can include traffic improvements, mobility improvements, mobility substitutes, (such as telecommuting and delivery services), and more accessible land use.

Accessibility is most difficult to measure because it is affected by the quality of various transport modes and land use factors. For example, employment accessibility must take into account the number of suitable jobs residents can reach within a reasonable commute time, by travel options that are adequately comfortable, affordable and safe. Although access is a well-recognized concept in the disciplines of geography and urban economics, it is a new concept for many transportation practitioners. In recent years transportation professionals have started exploring the implications of basing transport planning on access rather than traffic or mobility [BTS, 2001].

But only if transportation is defined in terms of accessibility rather than mobility can the full benefits of alternative modes and land use accessibility improvements be fully recognized. As long as mobility is considered an end in itself, rather than a means to an end, faster modes and more dispersed land use patterns will be favored over slower modes and more clustered land use in transportation planning and investment decisions.

3. The Role of Different Modes

Different transport modes play different roles in providing mobility and accessibility. For example, nonmotorized modes serve shorter-distance trips and motorized modes serve longer-distance mobility. Some modes are more suitable for people with physical disabilities or low incomes. Some modes are particularly important for certain industries.

Standard transport statistics indicate that motor vehicles are by far the most important form of transport, implying that other modes do little to provide accessibility. Travel surveys indicate that in most North American communities more than 90% of households own an automobile, and that more than 90% of trips are made by automobile, while only about 5% of trips are made by nonmotorized modes and less than 2% are made by transit. This suggests that the only way to significantly improve transport is to improve automobile travel, and that 90% or more of transport funding should be devoted to automobile-oriented improvements.

But the high priority given automobiles and the low priority given other modes is partly an artifact of how data are collected and presented. Most travel surveys only count the primary mode used between relatively large Transportation Analysis Zones (TAZs), and some only count peak-period travel or commute trips. As a result, they undercount shorter trips (those occurring within a TAZ), nonmotorized links of motorized trips, off-peak trips, non-work trips, travel by children, and recreational travel. Although only about 5% of trips are made exclusively by nonmotorized modes, about four times as many involve at least some walking or cycling on public right-of-way. For example, most surveys would not count a 5-minute walk from a parking space to a worksite, or a 10-minute walk from work to a nearby diner for lunch. If a traveler cycles 10 minutes to a bus stop, rides a bus for five minutes, and takes another 5-minute walk to their destination, this bike-transit-walk trip is usually coded simply as a transit trip, even though the nonmotorized links take more time than the motorized link.

Although most households own an automobile, many members of automobile-owning households cannot drive or must share a vehicles with other drivers. Motorists often use alternative modes when their automobile is unavailable due to a mechanical failure or other problems, and an increasing portion of travelers are choosing to walk, bicycle or use transit for personal or financial reasons, even if they have the option of driving. Although only about 2% of total trips are made by public transit, about 5% of US adults report that they rely primarily on public transit for transport, and 12% used public transit at least once during the previous two months. On busy urban corridors where traffic problems are greatest, transit often carries a significant portion of urban-peak travel.

In most communities, driving is relatively convenient and inexpensive except under urban-peak conditions, or for circulation within neighborhoods and commercial centers. These are exactly the situations in which transit and nonmotorized modes can be most effective. As a result, transit and nonmotorized improvements are often the best way to reduce current transport problems.