Geoscience Reference
In-Depth Information
transportation facilities, particularly constructing more and more highways (Boyce
and Kim
1987
). Planners frequently used transportation demand models that are
based on the “four-step” approaches for searching solutions for congestion. The
four-step models always result in more transportation facilities since the models
require the following inputs and trying to increase accessibility between origins and
destinations:
• Economic activities represented by land use.
• Number of households and/or housing units as origins for trips.
• Number of jobs and/or floor space of industries as destination for trips.
Once the number of origin and destination trips are exogenously given and then
ask for minimizing travel time between the two, one of the obvious and the most
frequently suggested solutions is the increase of transportation facilities to connect
the two activity sites. The four-step models also produce highway biased mode
choice since
• The mode choice algorithms are based on probabilities for choosing transporta-
tion mode by travelers,
• Probabilities are calculated based on the out-of-pocket trip cost, and
• The out-of-pocket cost does not represent the true social cost since gasoline price
in the USA does not represent the true economic cost.
In a typical analysis model for transportation demand such as in the four-step
models, modelers assume that travelers are rational and choose the alternative that
gives them the highest utility, frequently measures by travel time and out-of pocket
costs. Since travel time savings tend to be the largest element of benefits, the
alternative that gives the largest travel time saving is probably going to give the
largest benefit. In this process, automobile is usually perceived superior choice for
any given journey by the traveler since the door-to-door travel time is usually
shorter for automobile drivers due to a number of transfers, walking, and waiting
time which are a part of total travel time for mass transit. The optimal solution is
likely to be the one that attract more use of automobiles.
The fact that results from the trip generation step are used as given to the
consequence steps in mode choice, trip distribution and route choice implies that
transportation facilities should meet demand originating from residential areas
wherever and whenever developers choose to build. There is no policy variable
affecting the shape of urban form and structure in it nor there is any feed-back
mechanism how the four-step process results would affect land use decisions. In
fact, Boyce (
2002
) proved the counter-productivity of the four-step transportation
planning processes.
The inelasticity of travel cost with respect to the commuting distance (Litman
2013
) implies that people usually do not take the reduction in travel time as an
opportunity to spend the time saved in other activities: instead they tend to travel
further, sometimes as part of a long term decision about where to live. One could
argue that this has led to much greater benefits to those with high incomes than
those with low incomes and has contributed to the decentralization of urban areas
which makes it difficult to encourage people to switch from the car to alternative
modes. Thus, the conventional transportation planning model would most likely
recommend increase of highway capacities to connect the origin and destination,
