The document discusses factors that determine the demand for constructing a new highway between two cities. It analyzes three approaches: (1) land use, which considers how trips are generated and attracted based on land use types; (2) gravity model, where traffic flow increases with population size and decreases with distance; (3) competition with other modes like rail and air. The key reasons for a new highway are to reduce congestion, travel time and costs between the cities and increase interaction. The document estimates demand under each approach and identifies routes where highway demand would be highest.

1. TL1011
Assignment 2
Name: Thushan Dharmawardana
Index no: 101414G
Submission date: 22/11/2010

2. What is the objective of constructing a new highway?
Transport is an activity that is needed to attain some other work. Because of this reason we affirm
transport is a derived demand. With the rising population the demand for transport increases
proportionally. Assume that there are two cities A and B where the two cities are connected by a road
which doesn’t have enough capacity to accommodate the vehicle flow. Because of this there occurs lot
of issues about transportation. The issues can be stated as follows.
o Heavier traffic congestion.
o Larger travel, waiting and transfer time.
o Higher cost and opportunity cost.
o Lower utility level of passengers.
o Less interaction among the cities.
To overcome these issues a new highway can be constructed.
The demand for that highway can be estimated using following theories.
a. Land use approach
b. Gravity model
c. Economic theory
For instance assume that there are two cities A and B where those differ from each other when
considering socioeconomic cultural and other parameters.
A B
a) Land use approach
This theory mainly explains how the trips are made between different land uses. Every terrain of land
has some use. Mainly land is used in agriculture, industrial, commercial and residential purposes. The
amount of trips generated and attracted differs according to land use. For example commercial area
attracts more trips than a residential area.
1. The reason for total trips
This depends mainly on the different land uses. For example assume A as city of Colombo and B as city
of Kandy. Colombo is more a commercial city and Kandy is more likely a cultural city. In this case
Colombo is the highest trip attractor because it is a commercial city vice versa Kandy is the highest trip
generator. The attraction and generation rate vary from each other and the models have to be calibrated
according to follows.
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3. The trip generation
Quantity number of persons
Quality distribution of population
Intensity Income, ownership of vehicles
The trip attraction
This differs according to the purpose of the trip
Trip attraction to an office in Colombo depends on
Quantity number of employees
Quality number of employees with own vehicles
Intensity nature of the business
Trip attraction to a cultural zone in Kandy depends on
Quantity number of persons willing to visit cultural zones
Quality number of people with own vehicles
Intensity the value of the cultural zone
As described above there are many causes for trip attraction and generation. As per the land use theory
the trip attraction and generation models should be calculated for each and every aspect of travel before
implementing a high way.
2. The reason for restraints to trips
As mentioned earlier land use approach is based on the trip end. If we consider a barren land the total
trips attracted and generated by that zone will be around zero. If a land is used for some antisocial
activity the trips attracted to that zone will be very low
No trip A land
without any
attraction or
A B use to the
generation society
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4. As we can observe from the above graph the undeveloped and unused lands are a restraint for total trips
between two zones. A highway definitely not joins a barren land and a land with use.
3. The competition with railways and air travel
Assume that there is a railway line and a highway newly built between Sri Lanka and India. Then there
would be a definite competition between these three modes. We can identify Sri Lanka as a more
recreational island where India is more religious and commercial city.
Sri Lanka India
Small population Large population
Low income levels of people High income levels
Higher price of goods Lower price
Less tourist destinations (religious) More tourist destinations
Higher value for trip generation model Higher value for trip attraction model
As shown above there would be more trips towards India that the density of travel desire lines would
increase for that side. So there would be more travel demand from Sri Lanka to India. There would be a
higher competition between the three modes from Sri Lanka to India. Usually air travel is more
expensive so Indians would demand for air travel while Sri Lankans would demand for highway and
railway. There would be a more competition between the high way and railway among Sri Lankan
population.
b) Gravity model
This theory illustrates how the traffic flow between two travels zones increases with the population mass
and the distance between two zones.
D12
City 2, pop 2
City 1, pop 1
The theory states that the traffic flow between two zones (generators and attractors) increases
multiplicatively with the population mass of travel zones and the traffic flow increases when two zones
are closer to each other.
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5. Functions of transport Page 5

6. 1. The reason for total trips
Consider the three countries A, B and C. The trips between these zones are as follows.
C
A
B
PA> PB > PC P - Population of each country
DAC <DBC =DABD- Distance between countries
TAC >TAB> TBC T- Traffic flow between countries
As shown in the graph the population in A is the highest. Because A and C are the closest as per the
gravity model the traffic flow between these two countries are the highest. The traffic flow between B
and C is the lowest according to the gravity model.
Assume that a new highway is built merging these three countries. The total trips between country A and
C are the highest so the demand for a new highway is higher between A and C countries.
2. The reason for restraint to trips
Low population
More restraint for
High distance between two travel trips
zones
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7. If we consider the above example of three countries it is clearly visible that when the distance between
two countries increases the traffic flow between those countries decreases conversely. When the
population decreases the traffic flow tends to decrease. The implementation of a new high way should
never be between two countries which are far away and with lesser population.
According to the gravity model distance and population are not only the measures of separation of two
travel zones regarding the restraint to mobility. The restraint to travel is usually measured by the time
and cost.
Assume that a person who uses the normal road which connects A and B have to spend a 1 hour and
Rs.30 for the completion of the journey.
Generalized cost = α + 30
1 hour and Rs.30
A B
α-value per an hour
Because it is necessary to convert these two units into one unit the concept of generalized costmakes
these two units to a one unit by giving a value to the time.
Assume that A, B are connected together by a new highway the time and cost would change.
If the new values are ½ an hour and Rs. 25 the generalized cost would be follows.
Generalized cost = α/2 + 25
½ an hour and Rs.25
A B
It is evident that α/2 + 25 < α + 50. That means the implementation of a highway would make the
generalized cost lower and the restraints for total trips lower and make the passengers utility level high.
3. The competition with railways and air travel
Assume the example of three countries above when estimating the travel demand the population and the
distance between each country should be considered. The demand between the three modes would differ
from route to route. As shown above there would be a higher demand for the highway and railway
between the countries A and C because those countries are very adjacent and the generalized cost is
lower. There would be a higher demand for air travel in the routes AB and BC. The reason for that is the
countries A and C are distant from country B and the generalized cost between routes AB and BC lower
in air travel because the travel is at a low level.
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8. c) Economic theory
This theory is a cost based approach to travel demand. This is based on the observation that transport is a
derived demand.
The demand for mode of transport available for the same trip has described by the above theory as mode
choice and the demand for travel via two or more routes to the destination has described by the route
choice.
1. The reason for total trips
As declared earlier transport is a thing use to attain some other work. Every person has needs, to fulfill
them they should transport from place to place.
Let us consider a very possible example of two cities A and B where city A produces tea and the citizens
of city B consumes tea.
Tea Tea
producer consumer
A B
The tea production has to be transported from A to B. If there isn’t a better connectivity between these
two cities the consumers of B have to pay a higher price for that commodity because the additional
transport cost added to the selling price. Also the vendors from city A cannot sell a large amount
because the demand for that good is lower. The execution of a new highway linking these two cities
would make the transport cost lower and the price of tea would decrease consequently the demand for
that commodity increases and the producers would also be stimulated to increase their production.
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9. As shown above the price will decrease and the supply will increase with the implementation of a new
highway.
2. The reason for restraint to trips
Assume that there are two cities P and Q where there is only English speaking population in city P. The
city Q consists of Sinhala speaking population. The cities are located very close to each other but the
demand for travel is at a low level because of the language variation there is a restraint for total trips
between cities P and Q so construction of a highway joining these two cities would not be a good idea.
If there is a market at point A all the people close to the market would come to purchase commodities
from that market. But the transport cost restraints people coming to that market. So there is a particular
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10. range where the customers spread around.
The range of
customers
before the
construction of
highway
The range of
customers after
the construction
of highway
As shown above that range of customers would increase by diminishing the restraint to travel if a new
highway is constructed.
3. The competition with railways and air travel
Railway
A High way B
Air travel
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11. As illustrated above there are 3 modes to travel from A to B. Each mode would give the user a different
utility level. The utility level is calculated by the fare for the mode, travel time for the mode and the
access time for the mode.
A person can travel from A to B by bus, train or airplane. If the model share for train and airplane is
high then there would be a lower demand for the highway.
Implementation of a new high way should be done if the model share for a vehicle on the high way is
high considering the railway and air travel.
As per the above three theories we can estimate the travel demand for a highway.
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