A Virtual travel survey:
evaluating the regional economic impact of Transit-based corridor development
The quantification in absolute values of the socio-economic consequences
of given regional growth strategy would be complex and highly subjective to the
beholder’s social, philosophical and political assumptions. A quantification in
dollar and cents the impact of each scenario would be impossible. Fortunately,
however, what we need is not an absolute value, but rather the relative value
among different scenarios.
Next, I will analyze principles of travel behavior and locational choice to develop a measure to compare different transportation/land-use scenarios.
HUMAN DECISION PROCESS, INTERACTION, ACTIVITIES AND TRANSPORTATION
All people engage daily in a variety of actions in response
to a number of desires, aspirations, and moral obligations, aimed at maximizing
perceived utility. Some courses of
action are chosen by thought, some by habit, some by instinct, but always with
the conscious or unconscious objective of maximizing overall perceived benefits
Urban space as maximixer of positive interactions
The utility of an interaction is dependent, among other things, on the proximity of interactor and interactees, and a preferred time of the interaction to take place. The following factors should be optimized to maximize utility:
Adequate Adjacency: “Interactor” and “Interactees” have to be within reach of each other, either through spatial adjacency or through virtual adjacency (telecommunications). A growing number of interactions are rich combinations of spatial and virtual communications that involve many senses and many “interactees”.
Adequate Timing: The level and positivity/negativity of the utility level varies with the time and duration at which it happens. Most interactions (or activities) have a time range within which the utility level remain somewhat constant, this allow for a scheduling flexibility of the “interactor”. Other interactions, like work, have specific peak times at which utility is maximized. In fact, I will have high utility only when arriving on time. This time range can consist of minutes (ex. catching a train) or days (ex. wash car) or weeks or months (ex. painting my bicycle).
Adequate connectivity and timing are obtained through timely movement of “interactor” and/or “interactees” to achieve spatial adjacency, and through telecommunications to achieve virtual adjacency.
The maximization of these utilities is the reason why people (“interactors”) move to certain places or travel to certain locations. In most cases the desire for travel is derived from the desire for a specific interaction, in rare cases it becomes both the means and the end (ex. a ride in the park).
Mostly, however, travel is a dis-utility we are prepared to sustain as a price to obtain a certain utility: it is a negative interaction we are prepared to sustain to be able to engage in a chosen activity.
The cost of providing adjacency to “interactor” and/or the “interactees” is borne by many different parties. For example, the cost of my driving to “interact” with people and tools at work is borne in part by the following: myself, by operating the car; my employer, by providing parking; society, by breathing the fumes.
Scheduling of activities and interactions
Both consciously and unconsciously, every person revises daily, weekly, monthly tentative schedules based on places they have/want to be, things they have/want to buy, people they have/want to meet, relatives they have/want to escort.
Since the utility of each activity varies through time in a different way, each can be defined by certain temporal characteristics:
· Duration: the duration of a certain activity is approximated in our “schedules”. Duration of activities might be more or less foreseeable. Its actual value is affected by a combination of external events and dynamic rescheduling.
· Priority Level & Time Range: Activities could be categorized as primary or discretional. Primary activities (work, study…) are those that have a very high utility attached to them. Our participation and/or timeliness in these activities have great impact on our utility levels. However, this simple classification does not describe precisely how the utility level of each activity varies in time. Some activities have a “time range”: a span of time (in hours, days, weeks, months) within which I can accommodate the activity maintaining equal utility; for example, grocery store hours are the time range for my grocery shopping activity. A single curve could represent all these factors by describing the utility/dis-utility of performing the activity at different time/dates.
A regional physical growth strategy should be based on the basis of how well it accommodates these “Wish/To-Do” Lists (i.e. how easy it is to participate in desires activities) of businesses and individuals.
Changes in regional transportation and/or land-use have
one major economic effect from which all other effects are derived: real estate
and land values.
Demographic Distribution & Equity Issues
People and businesses located on the affected
locations will directly suffer or enjoy those changes only if they own the
property or their rental agreements are somewhat “stabilized”. In fact,
in the case of leased property, the changed value of affected properties will
ultimately sustained by the owner through changes in demand. This change in
demand would result in an increase in the eventual rental rates to match new
LOCATION, LOCATION, LOCATION: EVALUATING a regional GROWTH STRATEGY THROUGH REAL ESTATE VALUES
Transportation and land-use spatial-temporal
relationships determine the availability and quality of any location time/place
· Regional Connectivity: It describes the relationship of a location to activity opportunities. A location has easy access to certain activity opportunities and uneasy to other. Regional connectivity is always a positive attribute; however, the connectivity to different activity type has different value to different demographics. The transportation system and land-use distribution in a regional area influence the potential utility of a location by determining the dis-utility levels that local residents (or “interactors”), have to endure to come into spatial adjacency of desired activities (or “interactees”).
· Local Proximity: It describes the relationship of a location with its immediate surroundings. It includes the effects of local connectivity, environmental impact and adjacency effects. Every location can sustain both utility and/or dis-utility from its local connectivity, proximity and adjacency to another. Therefore, local proximity is positive or negative. For example, being across from a house more beautiful than mine might increases the value of my own house; if that house were abandoned and decayed, instead, it would decrease it. In other instances, the relationship toward another activity could bring connectivity benefits and proximity dis-benefits. For example, being close to a convenience store might be convenient for access to shopping but might decrease household safety. The transportation system and land-use distribution affect the utility levels of locations by attaching to them specific positive or negative “interactees”. For example, a new transit system might “attach” a high level of noise to surrounding locations, or a new land-use reconfiguration might give condominium views of a park. In such case, the “interactors” using the site would have difficulties avoiding undesired interactions with noise or desired interactions with a good view.
However, transportation and land-use do not directly affect
the utility of interactors, but the utility of the locations where
interactors choose to locate. The “interactors”, in turn, choose a location
were quality of available interaction opportunities is highest to them,
relatively to its price.
MEASURING REGIONAL CONNECTIVITY OF PROPOSED URBAN GROWTH STRATEGY
To evaluate the effects of proposed transportation/Land-use
policies and investment planners have been using the “scenario” method:
different proposed alternatives, including a “no-change”, are compared by major
performance measures to assess their relative merits.
“Virtual activity survey”: a proposed connectivity measure for transportation/land-use scenarios
The connectivity benefits of a location are ultimately enjoyed
by the resident and businesses that locate there. Each individual and business
has different interaction needs, and therefore will take advantage of different
A new home location and new job location will be assigned to
each of the surveyed residents. A certain resident will be assigned a virtual
residential location, which mostly approximate his/her actual one in price,
connectivity and proximity profiles.
VIRTUAL vs. ACTUAL SURVEY
Next, virtual and actual activity surveys can be used to compare
the relative accessibility of each scenario. We can compare what are the
relative costs of providing a specific amount of spatial/temporal freedom to
participate in certain activities. Meaning, we can analyze the relative
costs in time and transportation expenses that the same individual occurs in
the two scenarios for the same time/place utilities.
· Weekly Total Difference by individual or group.
· Daily Total Differences by individual or group.
· Continuous charted weekly travel-time comparison.
· Comparisons across demographic groups.
· Comparisons across different activity types.
These measures can be used in the evaluation of a given
urban growth strategy, because they embed changes in regional and local
connectivity. These measures, supplemented by measures of proximity effects,
could give a comprehensive assessment of the impact of a certain strategy.
Data on actual survey, transportation networks and land-usage must be very detailed spatially and temporally for these methods to perform well. The location of both the traveler in time and of all potential destinations should be precisely defined and inserted in a GIS database.
Three data sets are needed:
Detailed Actual Activity Survey: Current Differential-GPS and cellular phone technologies allow tracking the movement of people within urban environments. Issues of accuracy, consistency, and privacy, are rapidly being confronted and resolved. Great commercial opportunities are pushing their developments.. In fact, a new Federal law requires that all cellular phone will be locatable within 125 meters by 2001 for 911-emergency service. USDOT will soon complete the installation of special radio transmitters that will allow the location of watch size D-GPS receivers within 4 ft. Within months these technologies might be precise enough to locate the exact establishment or land parcel where the traveler is at any given moment. Also, mode, time and duration of trip, as well as time and duration of activity would be automatically recorded. In fact, mode of travel can easily be established by the analysis of geocoded traveling speeds and patterns.. Comparing the traveler position with location of all suppliers we can establish if he is in a ice cream shop or a drugstore. To complement these data, the surveyed will be asked to confirmed tracking data and provide additional data, such as: name of place visited, detailed purpose of visit, company. Remote location would greatly diminish the burden on the surveyed individual, reducing the “non-response” problem.
Land/Space Utilization: Location and attributes of all activity opportunities should be recorded for actual and proposed scenarios. Bulkier, more expensive and more precise remote location receivers are used to geocode buildings, land parcels and transportation infrastructures. Their accuracy is important to be able to match it with travelers’ data to determine “hits”, or visits. Activity suppliers are geocoded and classified in essentially-substitutable categories. Suppliers in a same category offer very similar interaction opportunities (or similar goods and services).
In reality, no two suppliers are truly substitutable because of different quantity and/or variety (I might go to McDonald for their particular kind of junk food, not only because it is just another fast-food restaurant). We will assume, however, that these subjective preferences within essentially substitutable categories of suppliers are relatively weak (i.e. if I cannot access a McDonald, I will settle for a Burger King without much distress).
For example, grocery stores might be classified as “Big Box”, “Mum & Pa” or “gourmet” reflecting different clienteles.
Transportation Network: Network topology and performance should be defined for current and proposed scenarios. For the ACTUAL SURVEY, Topology can easily be acquired through remote location technologies and, for the most part, is already available for US urban areas.
Network performance (or estimated speed at a given time) is, instead, might be hard to measure.
In fact, the speed of auto links changes by hour of day, by day of the week, by season, by weather conditions, and so on. The main cause of this is the fact that flow in an auto-facility is restricted by high Volume/Capacity ratios: the number of cars on a given street at a given moment (when high enough) affects the level of flow at that same moment.
For the greatest majority of links, however, flow is fairly constant because Volume/Capacity is fairly low. Therefore, their speed through time can be reasonably approximated.
Other streets are affected by regular and/or occasional congestion, and a number of flow measurements might be required at different time of day, and day of week.
Therefore, data on current auto-links performance can be acquired; its precision will depend on the number of measurement performed, which in turn is bound to a data acquisition budget.
For the VIRTUAL SURVEY, the creation of a network performance for the proposed scenario is required. It requires that we predict the effects of given land-use and transportation changes on roads flow. This has traditionally been a very unlikely endeavor because of the many dynamic involved in the Volume/Capacity ratio and Down’s “Triple Convergence” effect.
It would be impossible to predict travel times and classify locations in order of connectivity, because the flow on each transportation segment could not be predicted.
If, instead, we are considering the impacts of a strongly non-auto-based Transportation/Land-use scenario,
our ability to simulate the actual survey is greatly improved.
We are able to measure changes in regional connectivity through the speeds of separate-ROW Transit, pedestrian and bicycling. They can be predicted because their Volume/Capacity ratio rarely reaches critical highs. With these modes, speeds can be defined given transit system design, schedules and frequencies, average walking and bicycling speeds. In fact, when transit enjoys a separate ROW, traffic signal preemption or a combination of short routing and traffic prioritization, their speeds in time can precisely be ascertained (see Fig. 1).
Such transit-based strategy should have as major outcome an increase in regional connectivity, for certain areas near transit nodes, through various intermodal combinations (transit/walk, car/transit/walk, bike/transit, etc.). Also, certain road links should improve their flow because of diminished car ownership and usage. For the “Triple Convergence” effect and other reasons, I would assume these changes in car flow to be a relatively minor connectivity improvement, and therefore can be just roughly approximated.
Given a the complete set of topological and attribute data, GIS computer software allows to precisely calculate the shortest paths between any given destination. Proximity and accessibility can be simulated. That can, in turn, be related with existing and proposed land utilization to define the spatial/temporal relationship of different locations.
This information can be combined in a number of ways to communicate the transit/pedestrian accessibility (i.e. the freedom to participate in desired activities). Exact time costs can be calculated for each potential trip, trip chain, trip tour.
All essential tools to perform our VIRTUAL ACTIVITY SURVEY are presently included in GIS software; some programming will be needed to automate many procedures.
Following is part of the spreadsheet model I have developed to automatically calculate the time needed to move through a transit/pedestrian network within GIS. Any change in the following attributes of the transit systems would automatically update the time costs associated with each link:
Figure 1: This GIS-based transit/pedestrian link time cost calculator enables to assess precisely the amount savings in traveling times brought by a high quality and frequent transit system
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