URBAN ENVIRONMENTAL MANAGEMENT AND PLANNING

New transportation infrastructure can help shape land uses by increasing the accessibility of sites and the mobility of site users.1 For example, on a highway corridor through undeveloped land, a new interchange increases the accessibility of sites in the vicinity, enabling their development. In addition, the new interchange offers some existing users of the highway network time savings over their current routes and destinations, thereby increasing demand for new development on these sites. These pressures can result in land development, often at quite a distance from the interchange. While the new interchange may represent a transportation agency’s good-faith effort to fulfill its charge of improving mobility, it also produces powerful effects on land use. Other transportation investments produce “induced growth” in similar ways.2 That growth can then contribute to undesired environmental outcomes. If not managed properly, habitat loss from new greenfield development can interfere with ecosystem functions, including support of fish and wildlife populations. Impervious surface canquickly grow to the point of degrading surface and ground water quality. Losses in open space, increases in the heat-island effect, and greater air pollution from higher amounts of vehicle travel can all degrade human and environmental health and community quality.3 Of course transportation investment cannot produce growth absent demand. That demand, and the land use policies that affect it, drive land use and resulting impacts.

Local policies may produce new development, creating new travel demand and taxing the existing transportation network. As a result, the transportation agency may be unable to maintain its level of service standards, leading users and the locality to call for expanded capacity. Thus begins again the cycle of new transportation projects that encounter environmental issues.

Accessibility (or just access) refers to the ability to reach desired goods, services, activities and destinations (collectively called opportunities). Access is the ultimate goal of most transportation, except a small portion of travel in which movement is an end in itself (jogging, horseback riding, pleasure drives), with no destination. This perspective assumes that improved access benefits society, and mobility is one way to achieve this goal. This perspective considers vehicle traffic a subset of mobility, and mobility a subset of accessibility.

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 travel options such as Transit, Ridesharing and Nonmotorized Modes; mobility substitutes such as Telework and Delivery Services; and strategies to increase land use Accessibility such as Smart Growth and Location Efficient Development. 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 longer trips or faster modes if shorter trips and slower modes provide adequate access. It considers Walkability to be a particularly important mode, because walking provides Basic Access, including connections between modes and to destinations. 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 favor different types of accessibility. The distribution of destinations, land use mix, network connectivity and walking conditions all affect transportation system performance. The best location for public facilities has a combination of convenient proximity, 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 and more accessible land use.

Measurement

Accessibility is evaluated based on the time, money, discomfort and risk (the generalized cost) required to reach opportunities. Individuals often think of it in terms of convenience, that is, the ease with which they can reach what they want. Accessibility is relatively difficult to measure because it is affected by a variety of transportation, economic and geographic factors. For example, access to employment is affected by an individual’s physical and economic abilities, the quality and cost of travel options that reach worksites, the feasibility of telework (which may allow employment for a firm that is physically difficult to reach), and the geographic location of suitable jobs. Activity-based travel Models and integrated transportation/land use models using detailed travel survey data are most suitable for quantifying accessibility. 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). Improved techniques are being developed to better evaluate Transportation Diversity, Transit and NonmotorizedLand Use Factors that affect transport. The Accessibility chapter describes how to calculate an Accessibility Index

Mobility refers to the movement of people or goods. It assumes that “travel” means person- or ton-miles, “trip” means person- or freight-vehicle trip. It assumes that any increase in travel mileage or speed benefits society.

Users

From this perspective, transport users are mainly motorists, since most person- and ton-miles are by motor vehicle, but recognizes that some people rely on non-automobile modes, and some areas have large numbers of transit, rideshare and cycling trips. It recognizes that a significant portion of people 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 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. 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 most important, but transit and HOV access are also desirable in areas where density and demographics concentrate enough riders. The best location for public facilities has a combination of convenient roadway access, adequate parking, transit service, and cycling routes.

Transport Problems and Solutions

A mobility perspective defines transportation problems in terms of constraints on physical movement, and so favors solutions that increase motor vehicle system capacity and speed, including road and parking facility improvements, transit and ridesharing improvements, high-speed train, aviation and intermodal connections. It gives 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 benefit non-drivers is to improve motorized transport, including automobile, transit and taxi modes, with more modest consideration of walking and cycling.

Measurement

(1) Traffic

Definition

Traffic refers to vehicle movement. This perspective assumes that “travel” means vehicle travel and “trip” means vehicle-trip. It assumes that increased vehicle mileage and speed benefits society.

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, defined as members of households that do not own an automobile.

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 for motorist to access parking facilities or as a form of recreation, and so devotes little transportation funds to nonmotorized facilities.

Land Use

This perspective evaluates land use primarily in terms of proximity to highways and parking supply. The best location for a public facility is along a major arterial or freeway intersection, in an area with abundant parking supply. Downtown locations are undesirable due to excessive 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 traffic speeds, vehicle ownership, and the affordability of driving. From this perspective, the best way to benefit non-drivers is to help them become motorists, by making automobile and taxi travel convenient and inexpensive.

Measurement