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Fundamentals of

Transportation

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Fundamentals of Transportation

2

Fundamentals of Transportation

Fundamentals of Transportation

/About/

/Introduction/

/Economics/

/Geography and Networks/

/Planning/

/Trip Generation/

/Destination Choice/

/Mode Choice/

/Route Choice/

/Evaluation/

/Operations/

/Queueing/

/Traffic Flow/

/Queueing and Traffic Flow/

/Shockwaves/

/Traffic Signals/

/Design/

/Sight Distance/

/Grade/

/Earthwork/

/Horizontal Curves/

/Vertical Curves/

Other Topics

/Pricing/

/Conclusions/

/Analogs/

/Decision Making/

Fundamentals of Transportation/About

3

Fundamentals of Transportation/

About

This book is aimed at undergraduate civil engineering students, though the material may

provide a useful review for practitioners and graduate students in transportation. Typically, this would be for an Introduction to Transportation course, which might be taken by most students in their sophomore or junior year. Often this is the first engineering course students take, which requires a switch in thinking from simply solving given problems to formulating the problem mathematically before solving it, i.e. from straight-forward

calculation often found in undergraduate Calculus to vaguer word problems more reflective of the real world.

How an idea becomes a road

The plot of this textbook can be thought of as "How an idea becomes a road". The book begins with the generation of ideas. This is followed by the analysis of ideas, first

determining the origin and destination of a transportation facility (usually a road), then the required width of the facility to accommodate demand, and finally the design of the road in terms of curvature. As such the book is divided into three main parts: planning, operations, and design, which correspond to the three main sets of practitioners within the

transportation engineering community: transportation planners, traffic engineers, and

highway engineers. Other topics, such as pavement design, and bridge design, are beyond

the scope of this work. Similarly transit operations and railway engineering are also large topics beyond the scope of this book.

Each page is roughly the notes from one fifty-minute lecture.

Authors

Authors of this book include David Levinson [1], Henry Liu [2], William Garrison [3], Adam

Danczyk, Michael Corbett

References

[1] http://nexus.umn.edu

[2] http://www.ce.umn.edu/~liu/

[3] http://en.wikipedia.org/wiki/William_Garrison_(geographer)

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Fundamentals of Transportation/Introduction

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Fundamentals of Transportation/

Introduction

Transportation moves people

and goods from one place to

another using a variety of

vehicles across different

infrastructure systems. It does

this using not only technology

(namely vehicles, energy, and

infrastructure), but also

people’s time and effort;

producing not only the desired

outputs of passenger trips and

freight shipments, but also

adverse outcomes such as air

pollution, noise, congestion,

crashes, injuries, and

fatalities.

Figure 1 illustrates the inputs,

outputs, and outcomes of

transportation. In the upper

left are traditional inputs

(infrastructure (including

pavements, bridges, etc.),

Transportation inputs and outputs

labor required to produce

transportation, land consumed

by infrastructure, energy inputs, and vehicles). Infrastructure is the traditional preserve of civil engineering, while vehicles are anchored in mechanical engineering. Energy, to the extent it is powering existing vehicles is a mechanical engineering question, but the design of systems to reduce or minimize energy consumption require thinking beyond traditional

disciplinary boundaries.

On the top of the figure are Information, Operations, and Management, and Travelers’ Time and Effort. Transportation systems serve people, and are created by people, both the system owners and operators, who run, manage, and maintain the system and travelers who use it.

Travelers’ time depends both on freeflow time, which is a product of the infrastructure

design and on delay due to congestion, which is an interaction of system capacity and its use. On the upper right side of the figure are the adverse outcomes of transportation, in particular its negative externalities:

• by polluting, systems consume health and increase morbidity and mortality;

• by being dangerous, they consume safety and produce injuries and fatalities;

• by being loud they consume quiet and produce noise (decreasing quality of life and

property values); and

• by emitting carbon and other pollutants, they harm the environment.

Fundamentals of Transportation/Introduction

5

All of these factors are increasingly being recognized as costs of transportation, but the most notable are the environmental effects, particularly with concerns about global climate change. The bottom of the figure shows the outputs of transportation. Transportation is

central to economic activity and to people’s lives, it enables them to engage in work, attend school, shop for food and other goods, and participate in all of the activities that comprise human existence. More transportation, by increasing accessibility to more destinations,

enables people to better meet their personal objectives, but entails higher costs both

individually and socially. While the “transportation problem” is often posed in terms of congestion, that delay is but one cost of a system that has many costs and even more

benefits. Further, by changing accessibility, transportation gives shape to the development of land.

Modalism and Intermodalism

Transportation is often divided into infrastructure modes: e.g. highway, rail, water, pipeline and air. These can be further divided. Highways include different vehicle types: cars, buses, trucks, motorcycles, bicycles, and pedestrians. Transportation can be further separated into freight and passenger, and urban and inter-city. Passenger transportation is divided in

public (or mass) transit (bus, rail, commercial air) and private transportation (car, taxi, general aviation).

These modes of course intersect and interconnect. At-grade crossings of railroads and

highways, inter-modal transfer facilities (ports, airports, terminals, stations).

Different combinations of modes are often used on the same trip. I may walk to my car,

drive to a parking lot, walk to a shuttle bus, ride the shuttle bus to a stop near my building, and walk into the building where I take an elevator.

Transportation is usually considered to be between buildings (or from one address to

another), although many of the same concepts apply within buildings. The operations of an elevator and bus have a lot in common, as do a forklift in a warehouse and a crane at a port.

Motivation

Transportation engineering is usually taken by undergraduate Civil Engineering students.

Not all aim to become transportation professionals, though some do. Loosely, students in this course may consider themselves in one of two categories: Students who intend to

specialize in transportation (or are considering it), and students who don't. The remainder of civil engineering often divides into two groups: "Wet" and "Dry". Wets include those studying water resources, hydrology, and environmental engineering, Drys are those

involved in structures and geotechnical engineering.

Transportation students

Transportation students have an obvious motivation in the course above and beyond the

fact that it is required for graduation. Transportation Engineering is a pre-requisite to further study of Highway Design, Traffic Engineering, Transportation Policy and Planning, and Transportation Materials. It is our hope, that by the end of the semester, many of you will consider yourselves Transportation Students. However not all will.

Fundamentals of Transportation/Introduction

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"Wet Students"

I am studying Environmental Engineering or Water Resources, why should I care about

Transportation Engineering?

Transportation systems have major environmental impacts (air, land, water), both in their construction and utilization. By understanding how transportation systems are designed

and operate, those impacts can be measured, managed, and mitigated.

"Dry Students"

I am studying Structures or Geomechanics, why should I care about Transportation

Engineering?

Transportation systems are huge structures of themselves, with very specialized needs and constraints. Only by understanding the systems can the structures (bridges, footings,

pavements) be properly designed. Vehicle traffic is the dynamic structural load on these structures.

Citizens and Taxpayers

Everyone participates in society and uses transportation systems. Almost everyone

complains about transportation systems. In developed countries you seldom here similar

levels of complaints about water quality or bridges falling down. Why do transportation

systems engender such complaints, why do they fail on a daily basis? Are transportation

engineers just incompetent? Or is something more fundamental going on?

By understanding the systems as citizens, you can work toward their improvement. Or at

least you can entertain your friends at parties

Goal

It is often said that the goal of Transportation Engineering is "The Safe and Efficient Movement of People and Goods."

But that goal (safe and efficient movement of people and goods) doesn’t answer:

Who, What, When, Where, How, Why?

Overview

This wikibook is broken into 3 major units

Transportation Planning: Forecasting, determining needs and standards.

Traffic Engineering (Operations): Queueing, Traffic Flow Highway Capacity and Level of Service (LOS)

Highway Engineering (Design): Vehicle Performance/Human Factors, Geometric Design

Fundamentals of Transportation/Introduction

7

Thought Questions

• What constraints keeps us from achieving the goal of transportation systems?

• What is the "Transportation Problem"?

Sample Problem

• Identify a transportation problem (local, regional, national, or global) and consider

solutions. Research the efficacy of various solutions. Write a one-page memo

documenting the problem and solutions, documenting your references.

Abbreviations

• LOS - Level of Service

• ITE - Institute of Transportation Engineers

• TRB - Transportation Research Board

• TLA - Three letter abbreviation

Key Terms

• Hierarchy of Roads

• Functional Classification

• Modes

• Vehicles

• Freight, Passenger

• Urban, Intercity

• Public, Private

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Transportation Economics/Introduction

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Transportation Economics/

Introduction

Transportation systems are subject to constraints and face questions of resource allocation.

The topics of supply and demand, as well as equilibrium and disequilibrium, arise and give shape to the use and capability of the system.

Demand Curve

How much would people pay for a final grade of an A in a transportation engineering class?

• How many people would pay $5000 for an A?

• How many people would pay $500 for an A?

• How many people would pay $50 for an A?

• How many people would pay $5 for an A?

If we draw out these numbers, with the price on the Y-axis, and the number of people

willing to pay on the X-axis, we trace out a demand curve. Unless you run into an

exceptionally ethical (or hypocritical) group, the lower the price, the more people are

willing to pay for an "A". We can of course replace an "A" with any other good or service, such as the price of gasoline and get a similar though not identical curve.

Demand and Budgets in Transportation

We often say "travel is a derived demand". There would be no travel but for the activities being undertaken at the trip ends. Travel is seldom consumed for its own sake, the

occasional "Sunday Drive" or walk in the park excepted. On the other hand, there seems to be some innate need for people to get out of the house, a 20-30 minute separation between the home and workplace is common, and 60 - 90 minutes of travel per day total is common, even for nonworkers. We do know that the more expensive something is, the less of it that will be consumed. E.g. if gas prices were doubled there will be less travel overall. Similarly, the longer it takes to get from A to B, the less likely it is that people will go from A to B.

In short, we are dealing with a downward sloping demand curve, where the curve itself

depends not only on the characteristics of the good in question, but also on its complements or substitutes.

The Shape of Demand

What we need to estimate is the shape of demand (is it

linear or curved, convex or concave, what function best

describes it), the sensitivity of demand for a particular

thing (a mode, an origin destination pair, a link, a time

of day) to price and time (elasticity) in the short run and

the long run.

Demand for Travel

• Are the choices continuous (the number of miles

driven) or discrete (car vs. bus)?

• Are we treating demand as an absolute or a probability?

index-9_1.png

Transportation Economics/Introduction

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• Does the probability apply to individuals (disaggregate) or the population as a whole

(aggregate)?

• What is the trade-off between money and time?

• What are the effects on demand for a thing as a function of the time and money costs of competitive or complementary choices (cross elasticity).

Supply Curve

How much would a person need to pay you to write an A-quality 20 page term paper for a

given transportation class?

• How many would write it for $100,000?

• How many would write it for $10,000?

• How many would write it for $1,000?

• How many would write it for $100?

• How many would write it for $10?

If we draw out these numbers for all the potential entrepreneurial people available, we

trace out a supply curve. The lower the price, the fewer people are willing to supply the paper-writing service.

Equilibrium in a Negative Feedback System

Supply and Demand comprise the economists view of

transportation systems. They are equilibrium systems.

What does that mean?

It means the system is subject to a negative feedback

process:

An increase in A begets a decrease in B. An increase B

begets an increase in A.

Example: A: Traffic Congestion and B: Traffic Demand

... more congestion limits demand, but more demand

creates more congestion.

Negative feedback loop

Supply and Demand Equilibrium

As with earning grades and cheating, transportation is not free, it costs both time and

money. These costs are represented by a supply curve, which rises with the amount of

travel demanded. As described above, demand (e.g. the number of vehicles which want to

use the facility) depends on the price, the lower the price, the higher the demand. These two curves intersect at an equilibrium point. In the example figure, they intersect at a toll of $0.50 per km, and flow of 3000 vehicles per hour. Time is usually converted to money

(using a Value of Time), to simplify the analysis.

index-10_1.png

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Transportation Economics/Introduction

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Costs may be variable and include users' time,

out-of-pockets costs (paid on a per trip or per distance

basis) like tolls, gasolines, and fares, or fixed like

insurance or buying an automobile, which are only

borne once in a while and are largely independent of

the cost of an individual trip.

Disequilibrium

However, many elements of the transportation system

Illustration of equilibrium between

do not necessarily generate an equilibrium. Take the

supply and demand

case where an increase in A begets an increase in B. An

increase in B begets an increase in A. An example

where A an increase in Traffic Demand generates more Gas Tax Revenue ( B) more Gas Tax Revenue generates more Road Building, which in turn increases traffic demand. (This

example assumes the gas tax generates more demand from the resultant road building than

costs in sensitivity of demand to the price, i.e. the investment is worthwhile). This is dubbed a positive feedback system, and in some contexts a "Virtuous Circle", where the "virtue" is a value judgment that depends on your perspective.

Similarly, one might have a "Vicious Circle" where a decrease in A begets a decrease in B

and a decrease in B begets a decrease in A. A classic example of this is where ( A) is Transit Service and ( B) is Transit Demand. Again "vicious" is a value judgment. Less service results in fewer transit riders, fewer transit riders cannot make as a great a claim on

transportation resources, leading to more service cutbacks.

These systems of course interact: more road building may attract transit riders to cars, while those additional drivers pay gas taxes and generate more roads.

One might ask whether positive feedback systems

converge or diverge. The answer is "it depends on the

system", and in particular where or when in the system

you observe. There might be some point where no

matter how many additional roads you built, there

would be no more traffic demand, as everyone already

consumes as much travel as they want to. We have yet

to reach that point for roads, but on the other hand, we

have for lots of goods. If you live in most parts of the

United States, the price of water at your house

probably does not affect how much you drink, and a

lower price for tap water would not increase your rate

of ingestion. You might use substitutes if their prices

Positive feedback loop (virtuous circle)

were lower (or tap water were costlier), e.g. bottled

water. Price might affect other behaviors such as lawn

watering and car washing though.

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index-11_2.jpg

Transportation Economics/Introduction

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Provision

Transportation services are provided by both the public

and private sector.

• Roads are generally publicly owned in the United

States, though the same is not true of highways in

other countries. Furthermore, public ownership has

not always been the norm, many countries had a long

history of privately owned turnpikes, in the United

States private roads were known through the early

1900s.

• Railroads are generally private.

• Carriers (Airlines, Bus Companies, Truckers, Train

Positive feedback loop (vicious circle)

Operators) are often private firms

• Formerly private urban transit operators have been taken over by local government from the 1950s in a process called municipalization. With the rise of the automobile, transit systems were steadily losing passengers and money.

The situation is complicated by the idea of contracting or franchising. Often private firms operate "public transit" routes, either under a contract, for a fixed price, or an agreement where the private firm collects the revenue on the route (a franchise agreement).

Franchises may be subsidized if the route is a money-loser, or may require bidding if the route is profitable. Private provision of public transport is common in the United Kingdom.

Thought questions

1. Should the government subsidize public

transportation? Why or why not?

2. Should the government operate public

transportation systems?

3. Is building roads a good idea even if it results in

more travel demand?

Sample Problem

Problem (Solution)

London Routemaster Bus

Transportation Economics/Introduction

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Key Terms

• Supply

• Demand

• Negative Feedback System

• Equilibrium

• Disequilibrium

• Public Sector

• Private Sector

Fundamentals of Transportation/

Geography and Networks

Transportation systems have specific structure. Roads have length, width, and depth. The characteristics of roads depends on their purpose.

Roads

A road is a path connecting two points. The English word ‘road’ comes from the same root as the word ‘ride’ –the Middle English ‘rood’ and Old English ‘rad’ –meaning the act of

riding. Thus a road refers foremost to the right of way between an origin and destination. In an urban context, the word street is often used rather than road, which dates to the Latin word ‘strata’, meaning pavement (the additional layer or stratum that might be on top of a path).

Modern roads are generally paved, and unpaved routes are considered trails. The pavement of roads began early in history. Approximately 2600 BCE, the Egyptians constructed a

paved road out of sandstone and limestone slabs to assist with the movement of stones on rollers between the quarry and the site of construction of the pyramids. The Romans and

others used brick or stone pavers to provide a more level, and smoother surface, especially in urban areas, which allows faster travel, especially of wheeled vehicles. The innovations of Thomas Telford and John McAdam reinvented roads in the early nineteenth century, by

using less expensive smaller and broken stones, or aggregate, to maintain a smooth ride

and allow for drainage. Later in the nineteenth century, application of tar (asphalt) further smoothed the ride. In 1824, asphalt blocks were used on the Champs-Elysees in Paris. In

1872, the first asphalt street (Fifth Avenue) was paved in New York (due to Edward de

Smedt), but it wasn’t until bicycles became popular in the late nineteenth century that the

“Good Roads Movement” took off. Bicycle travel, more so than travel by other vehicles at the time, was sensitive to rough roads. Demands for higher quality roads really took off with the widespread adoption of the automobile in the United States in the early twentieth century.

The first good roads in the twentieth century were constructed of Portland cement concrete (PCC). The material is stiffer than asphalt (or asphalt concrete) and provides a smoother ride. Concrete lasts slightly longer than asphalt between major repairs, and can carry a heavier load, but is more expensive to build and repair. While urban streets had been paved with concrete in the US as early as 1889, the first rural concrete road was in Wayne

County, Michigan, near to Detroit in 1909, and the first concrete highway in 1913 in Pine Fundamentals of Transportation/Geography and Networks

13

Bluff, Arkansas. By the next year over 2300 miles of concrete pavement had been layed

nationally. However over the remainder of the twentieth century, the vast majority of

roadways were paved with asphalt. In general only the most important roads, carrying the heaviest loads, would be built with concrete.

Roads are generally classified into a hierarchy. At the top of the hierarchy are freeways, which serve entirely a function of moving vehicles between other roads. Freeways are

grade-separated and limited access, have high speeds and carry heavy flows. Below

freeways are arterials. These may not be grade-separated, and while access is still

generally limited, it is not limited to the same extent as freeways, particularly on older roads. These serve both a movement and an access function. Next are collector/distributor roads. These serve more of an access function, allowing vehicles to access the network from origins and destinations, as well as connecting with smaller, local roads, that have only an access function, and are not intended for the movement of vehicles with neither a local

origin nor destination. Local roads are designed to be low speed and carry relatively little traffic.

The class of the road determines which level of government administers it. The highest

roads will generally be owned, operated, or at least regulated (if privately owned) by the higher level of government involved in road operations; in the United States, these roads are operated by the individual states. As one moves down the hierarchy of roads, the level of government is generally more and more local (counties may control collector/distributor roads, towns may control local streets). In some countries freeways and other roads near the top of the hierarchy are privately owned and regulated as utilities, these are generally operated as toll roads. Even publicly owned freeways are operated as toll roads under a toll authority in other countries, and some US states. Local roads are often owned by adjoining property owners and neighborhood associations.

The design of roads is specified in a number of design manual, including the AASHTO

Policy on the Geometric Design of Streets and Highways (or Green Book). Relevant

concerns include the alignment of the road, its horizontal and vertical curvature, its

super-elevation or banking around curves, its thickness and pavement material, its

cross-slope, and its width.

Freeways

A motorway or freeway (sometimes called an expressway or thruway) is a multi-lane divided road that is designed to be high-speed free flowing, access-controlled, built to high

standards, with no traffic lights on the mainline. Some motorways or freeways are financed with tolls, and so may have tollbooths, either across the entrance ramp or across the

mainline. However in the United States and Great Britain, most are financed with gas or

other tax revenue.

Though of course there were major road networks during the Roman Empire and before,

the history of motorways and freeways dates at least as early as 1907, when the first

limited access automobile highway, the Bronx River Parkway began construction in

Westchester County, New York (opening in 1908). In this same period, William Vanderbilt

constructed the Long Island Parkway as a toll road in Queens County, New York. The Long

Island Parkway was built for racing and speeds of 60 miles per hour (96 km/hr) were

accommodated. Users however had to pay a then expensive $2.00 toll (later reduced) to

recover the construction costs of $2 million. These parkways were paved when most roads

Fundamentals of Transportation/Geography and Networks

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were not. In 1919 General John Pershing assigned Dwight Eisenhower to discover how

quickly troops could be moved from Fort Meade between Baltimore and Washington to the

Presidio in San Francisco by road. The answer was 62 days, for an average speed of 3.5

miles per hour (5.6 km/hr). While using segments of the Lincoln Highway, most of that road was still unpaved. In response, in 1922 Pershing drafted a plan for an 8,000 mile (13,000

km) interstate system which was ignored at the time.

The US Highway System was a set of paved and consistently numbered highways sponsored

by the states, with limited federal support. First built in 1924, they succeeded some

previous major highways such as the Dixie Highway, Lincoln Highway and Jefferson

Highway that were multi-state and were constructed with the aid of private support. These roads however were not in general access-controlled, and soon became congested as

development along the side of the road degraded highway speeds.

In parallel with the US Highway system, limited access parkways were developed in the

1920s and 1930s in several US cities. Robert Moses built a number of these parkways in

and around New York City. A number of these parkways were grade separated, though they

were intentionally designed with low bridges to discourage trucks and buses from using

them. German Chancellor Adolf Hitler appointed a German engineer Fritz Todt Inspector

General for German Roads. He managed the construction of the German Autobahns, the

first limited access high-speed road network in the world. In 1935, the first section from Frankfurt am Main to Darmstadt opened, the total system today has a length of 11,400 km.

The Federal-Aid Highway Act of 1938 called on the Bureau of Public Roads to study the

feasibility of a toll-financed superhighway system (three east-west and three north-south routes). Their report Toll Roads and Free Roads declared such a system would not be

self-supporting, advocating instead a 43,500 km (27,000 mile) free system of interregional highways, the effect of this report was to set back the interstate program nearly twenty years in the US.

The German autobahn system proved its utility during World War II, as the German army

could shift relatively quickly back and forth between two fronts. Its value in military

operations was not lost on the American Generals, including Dwight Eisenhower.

On October 1, 1940, a new toll highway using the old, unutilized South Pennsylvania

Railroad right-of-way and tunnels opened. It was the first of a new generation of limited access highways, generally called superhighways or freeways that transformed the

American landscape. This was considered the first freeway in the US, as it, unlike the

earlier parkways, was a multi-lane route as well as being limited access. The Arroyo Seco Parkway, now the Pasadena Freeway, opened December 30, 1940. Unlike the Pennsylvania

Turnpike, the Arroyo Seco parkway had no toll barriers.

A new National Interregional Highway Committee was appointed in 1941, and reported in

1944 in favor of a 33,900 mile system. The system was designated in the Federal Aid

Highway Act of 1933, and the routes began to be selected by 1947, yet no funding was

provided at the time. The 1952 highway act only authorized a token amount for

construction, increased to $175 million annually in 1956 and 1957.

The US Interstate Highway System was established in 1956 following a decade and half of

discussion. Much of the network had been proposed in the 1940s, but it took time to

authorize funding. In the end, a system supported by gas taxes (rather than tolls), paid for 90% by the federal government with a 10% local contribution, on a pay-as-you-go” system, was established. The Federal Aid Highway Act of 1956 had authorized the expenditure of

Fundamentals of Transportation/Geography and Networks

15

$27.5 billion over 13 years for the construction of a 41,000 mile interstate highway system.

As early as 1958 the cost estimate for completing the system came in at $39.9 billion and the end date slipped into the 1980s. By 1991, the final cost estimate was $128.9 billion.

While the freeways were seen as positives in most parts of the US, in urban areas

opposition grew quickly into a series of freeway revolts. As soon as 1959, (three years after the Interstate act), the San Francisco Board of Supervisors removed seven of ten freeways from the city’s master plan, leaving the Golden Gate bridge unconnected to the freeway

system. In New York, Jane Jacobs led a successful freeway revolt against the Lower

Manhattan Expressway sponsored by business interests and Robert Moses among others. In

Baltimore, I-70, I-83, and I-95 all remain unconnected thanks to highway revolts led by now Senator Barbara Mikulski. In Washington, I-95 was rerouted onto the Capital Beltway. The pattern repeated itself elsewhere, and many urban freeways were removed from Master

Plans.

In 1936, the Trunk Roads Act ensured that Great Britain’s Minister of Transport controlled about 30 major roads, of 7,100 km (4,500 miles) in length. The first Motorway in Britain, the Preston by-pass, now part of the M-6, opened in 1958. In 1959, the first stretch of the M1 opened. Today there are about 10,500 km (6300 miles) of trunk roads and motorways in

England.

Australia has 790 km of motorways, though a much larger network of roads. However the

motorway network is not truly national in scope (in contrast with Germany, the United

States, Britain, and France), rather it is a series of local networks in and around

metropolitan areas, with many intercity connection being on undivided and non-grade

separated highways. Outside the Anglo-Saxon world, tolls were more widely used. In Japan, when the Meishin Expressway opened in 1963, the roads in Japan were in far worse shape

than Europe or North American prior to this. Today there are over 6,100 km of expressways (3,800 miles), many of which are private toll roads. France has about 10,300 km of

expressways (6,200 miles) of motorways, many of which are toll roads. The French

motorway system developed through a series of franchise agreements with private

operators, many of which were later nationalized. Beginning in the late 1980s with the

wind-down of the US interstate system (regarded as complete in 1990), as well as intercity motorway programs in other countries, new sources of financing needed to be developed.

New (generally suburban) toll roads were developed in several metropolitan areas.

An exception to the dearth of urban freeways is the case of the Big Dig in Boston, which relocates the Central Artery from an elevated highway to a subterranean one, largely on the same right-of-way, while keeping the elevated highway operating. This project is estimated to be completed for some $14 billion; which is half the estimate of the original complete US

Interstate Highway System.

As mature systems in the developed countries, improvements in today’s freeways are not so much widening segments or constructing new facilities, but better managing the roadspace that exists. That improved management, takes a variety of forms. For instance, Japan has advanced its highways with application of Intelligent Transportation Systems, in particular traveler information systems, both in and out of vehicles, as well as traffic control systems.

The US and Great Britain also have traffic management centers in most major cities that

assess traffic conditions on motorways, deploy emergency vehicles, and control systems like ramp meters and variable message signs. These systems are beneficial, but cannot be seen as revolutionizing freeway travel. Speculation about future automated highway systems has Fundamentals of Transportation/Geography and Networks

16

taken place almost as long as highways have been around. The Futurama exhibit at the

New York 1939 World’s Fair posited a system for 1960. Yet this technology has been twenty years away for over sixty years, and difficulties remain.

Layers of Networks

The road is itself part of a layer of subsystems of which the pavement surface is only one part. We can think of a hierarchy of systems.

• Places

• Trip Ends

• End to End Trip

• Driver/Passenger

• Service (Vehicle & Schedule)

• Signs and Signals

• Markings

• Pavement Surface

• Structure (Earth & Pavement and Bridges)

• Alignment (Vertical and Horizontal)

• Right-Of-Way

• Space

At the base is space. On space, a specific right-of-way is designated, which is property where the road goes. Originally right-of-way simply meant legal permission for travelers to cross someone's property. Prior to the construction of roads, this might simply be a

well-worn dirt path.

On top of the right-of-way is the alignment, the specific path a transportation facility takes within the right-of-way. The path has both vertical and horizontal elements, as the road rises or falls with the topography and turns as needed.

Structures are built on the alignment. These include the roadbed as well as bridges or tunnels that carry the road.

Pavement surface is the gravel or asphalt or concrete surface that vehicles actually ride upon and is the top layer of the structure. That surface may have markings to help guide drivers to stay to the right (or left), delineate lanes, regulate which vehicles can use which lanes (bicycles-only, high occupancy vehicles, buses, trucks) and provide additional

information. In addition to marking, signs and signals to the side or above the road provide additional regulatory and navigation information.

Services use roads. Buses may provide scheduled services between points with stops along the way. Coaches provide scheduled point-to-point without stops. Taxis handle irregular

passenger trips.

Drivers and passengers use services or drive their own vehicle (producing their own transportation services) to create an end-to-end trip, between an origin and destination.

Each origin and destination comprises a trip end and those trip ends are only important because of the places at the ends and the activity that can be engaged in. As transportation is a derived demand, if not for those activities, essentially no passenger travel would be undertaken.

With modern information technologies, we may need to consider additional systems, such

as Global Positioning Systems (GPS), differential GPS, beacons, transponders, and so on

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Fundamentals of Transportation/Geography and Networks

17

that may aide the steering or navigation processes. Cameras, in-pavement detectors, cell phones, and other systems monitor the use of the road and may be important in providing

feedback for real-time control of signals or vehicles.

Each layer has rules of behavior:

• some rules are physical and never violated, others are physical but probabilistic

• some are legal rules or social norms which are occasionally violated

Hierarchy of Roads

Even within each layer of the

system of systems described

above, there is differentiation.

Transportation facilities have

two distinct functions: through

movement and land access.

This differentiation:

• permits the aggregation of

traffic to achieve economies

of scale in construction and

operation (high speeds);

• reduces the number of

conflicts;

• helps maintain the desired

quiet character of

Hierarchy of roads

residential neighborhoods

by keeping through traffic away from homes;

• contains less redundancy, and so may be less costly to build.

Functional Classification

Types of Connections

Relation to Abutting

Minnesota

Property

Examples

Limited Access (highway)

Through traffic movement

Limited or controlled access

I-94, Mn280

between cities and across

highways with ramps and/or

cities

curb cut controls.

Linking (arterial:principal

Traffic movement between

Direct access to abutting

University Avenue,

and minor)

limited access and local

property.

Washington Avenue

streets.

Local (collector and

Traffic movement in and

Direct access to abutting

Pillsbury Drive,

distributor roads)

between residential areas

property.

17th Avenue

Fundamentals of Transportation/Geography and Networks

18

Model Elements

Transportation forecasting, to be discussed in more depth in subsequent modules, abstracts the real world into a simplified representation.

Recall the hierarchy of roads. What can be simplified? It is typical for a regional forecasting model to eliminate local streets and replace them with a centroid (a point representing a traffic analysis zone). Centroids are the source and sink of all transportation demand on the network. Centroid connectors are artificial or dummy links connecting the centroid to the

"real" network. An illustration of traffic analysis zones can be found at this external link for Fulton County, Georgia, here: traffic zone map, 3MB [1]. Keep in mind that Models are abstractions.

Network

• Zone Centroid - special node whose number identifies a zone, located by an "x" "y"

coordinate representing longitude and latitude (sometimes "x" and "y" are identified using planar coordinate systems).

• Node (vertices) - intersection of links , located by x and y coordinates

• Links (arcs) - short road segments indexed by from and to nodes (including centroid

connnectors), attributes include lanes, capacity per lane, allowable modes

• Turns - indexed by at, from, and to nodes

• Routes, (paths) - indexed by a series of nodes from origin to destination. (e.g. a bus route)

• Modes - car, bus, HOV, truck, bike, walk etc.

Matrices

Scalar

A scalar is a single value that applies model-wide; e.g. the price of gas or total trips.

Total Trips

Variable

T

Vectors

Vectors are values that apply to particular zones in the model system, such as trips

produced or trips attracted or number of households. They are arrayed separately when

treating an zone as an origin or as a destination so that they can be combined into full matrices.

• vector (origin) - a column of numbers indexed by traffic zones, describing attributes at the origin of the trip (e.g. the number of households in a zone)

Trips Produced at Origin Zone

Origin Zone 1

Ti1

Origin Zone 2

Ti2

Origin Zone 3

Ti3

• vector (destination) - a row of numbers indexed by traffic zones, describing attributes at the destination

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Fundamentals of Transportation/Geography and Networks

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Destination Zone 1

Destination Zone 2

Destination Zone 3

Trips Attracted to

Tj1

Tj2

Tj3

Destination Zone

Full Matrices

A full or interaction matrix is a table of numbers, describing attributes of the

origin-destination pair

Destination Zone 1

Destination Zone 2

Destination Zone 3

Origin Zone 1

T11

T12

T13

Origin Zone 2

T21

T22

T23

Origin Zone 3

T31

T32

T33

Thought Questions

• Identify the rules associated with each layer?

• Why aren’t all roads the same?

• How might we abstract the real transportation system when representing it in a model

for analysis?

• Why is abstraction useful?

Variables

- Total Trips

- Trips Produced from Origin Zone k

- Trips Attracted to Destination Zone k

- Trips Going Between Origin Zone i and Destination Zone j

Key Terms

• Zone Centroid

• Node

• Links

• Turns

• Routes

• Modes

• Matrices

• Right-of-way

• Alignment

• Structures

• Pavement Surface

• Markings

• Signs and Signals

• Services

• Driver

• Passenger

• End to End Trip

Fundamentals of Transportation/Geography and Networks

20

• Trip Ends

• Places

External Exercises

Use the ADAM software at the STREET website [2] and examine the network structure.

Familiarize yourself with the software, and edit the network, adding at least two nodes and four one-way links (two two-way links), and deleting nodes and links. What are the

consequences of such network adjustments? Are some adjustments better than others?

References

[1] http://wms.co.fulton.ga.us/apps/doc_archive/get.php/69253.pdf

[2] http://street.umn.edu

Fundamentals of Transportation/Trip

Generation

Trip Generation is the first step in the conventional four-step transportation forecasting process (followed by Destination Choice, Mode Choice, and Route Choice), widely used for

forecasting travel demands. It predicts the number of trips originating in or destined for a particular traffic analysis zone.

Every trip has two ends, and we need to know where both of them are. The first part is

determining how many trips originate in a zone and the second part is how many trips are destined for a zone. Because land use can be divided into two broad category (residential and non-residential)<footnote>There are two types of people in the world, those that divide the world into two kinds of people and those that don't. Some people say there are three types of people in the world, those who can count, and those who can't.</footnote> we have models that are household based and non-household based (e.g. a function of number

of jobs or retail activity).

For the residential side of things, trip generation is thought of as a function of the social and economic attributes of households (households and housing units are very similar

measures, but sometimes housing units have no households, and sometimes they contain

multiple households, clearly housing units are easier to measure, and those are often used instead for models, it is important to be clear which assumption you are using).

At the level of the traffic analysis zone, the language is that of land uses "producing" or attracting trips, where by assumption trips are "produced" by households and "attracted" to non-households. Production and attractions differ from origins and destinations. Trips are produced by households even when they are returning home (that is, when the household is a destination). Again it is important to be clear what assumptions you are using.

Fundamentals of Transportation/Trip Generation

21

Activities

People engage in activities, these activities are the "purpose" of the trip. Major activities are home, work, shop, school, eating out, socializing, recreating, and serving passengers (picking up and dropping off). There are numerous other activities that people engage on a less than daily or even weekly basis, such as going to the doctor, banking, etc. Often less frequent categories are dropped and lumped into the catchall "Other".

Every trip has two ends, an origin and a destination. Trips are categorized by purposes, the activity undertaken at a destination location.

Observed trip making from the Twin Cities (2000-2001) Travel

Behavior Inventory by Gender

Trip Purpose

Males

Females

Total

Work

4008

3691

7691

Work related

1325

698

2023

Attending school

495

465

960

Other school activities

108

134

242

Childcare, daycare, after school care

111

115

226

Quickstop

45

51

96

Shopping

2972

4347

7319

Visit friends or relatives

856

1086

1942

Personal business

3174

3928

7102

Eat meal outside of home

1465

1754

3219

Entertainment, recreation, fitness

1394

1399

2793

Civic or religious

307

462

769

Pick up or drop off passengers

1612

2490

4102

With another person at their activities

64

48

112

At home activities

288

384

672

Some observations:

• Men and women behave differently, splitting responsibilities within households, and

engaging in different activities,

• Most trips are not work trips, though work trips are important because of their peaked nature (and because they tend to be longer in both distance and travel time),

• The vast majority of trips are not people going to (or from) work.

People engage in activities in sequence, and may chain their trips. In the Figure below, the trip-maker is traveling from home to work to shop to eating out and then returning home.

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Fundamentals of Transportation/Trip Generation

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Specifying Models

How do we predict how many trips will be generated by a zone? The number of trips

originating from or destined to a purpose in a zone are described by trip rates (a

cross-classification by age or demographics is often used) or equations. First, we need to identify what we think are the relevant variables.

Home-end

The total number of trips leaving or returning to homes in a zone may be described as a

function of:

Home-End Trips are sometimes functions of:

• Housing Units

• Household Size

• Age

• Income

• Accessibility

• Vehicle Ownership

• Other Home-Based Elements

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Fundamentals of Transportation/Trip Generation

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Work-end

At the work-end of work trips, the number of trips generated might be a function as below: Work-End Trips are sometimes functions of:

• Jobs

• Square Footage of Workspace

• Occupancy Rate

• Other Job-Related Elements

Shop-end

Similarly shopping trips depend on a number of factors:

Shop-End Trips are sometimes functions of:

• Number of Retail Workers

• Type of Retail Available

• Square Footage of Retail Available

• Location

• Competition

• Other Retail-Related Elements

Input Data

A forecasting activity conducted by planners or economists, such as one based on the

concept of economic base analysis, provides aggregate measures of population and activity growth. Land use forecasting distributes forecast changes in activities across traffic zones.

Estimating Models

Which is more accurate: the data or the average? The problem with averages (or

aggregates) is that every individual’s trip-making pattern is different.

Home-end

To estimate trip generation at the home end, a cross-classification model can be used, this is basically constructing a table where the rows and columns have different attributes, and each cell in the table shows a predicted number of trips, this is generally derived directly from data.

In the example cross-classification model: The dependent variable is trips per person. The independent variables are dwelling type (single or multiple family), household size (1, 2, 3, 4, or 5+ persons per household), and person age.

The figure below shows a typical example of how trips vary by age in both single-family and multi-family residence types.

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Fundamentals of Transportation/Trip Generation

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The figure below shows a moving average.

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Fundamentals of Transportation/Trip Generation

25

Non-home-end

The trip generation rates for both “work” and “other” trip ends can be developed using

Ordinary Least Squares (OLS) regression (a statistical technique for fitting curves to

minimize the sum of squared errors (the difference between predicted and actual value)

relating trips to employment by type and population characteristics.

The variables used in estimating trip rates for the work-end are Employment in Offices (

), Retail (

), and Other (

)

A typical form of the equation can be expressed as:

Where:

- Person trips attracted per worker in the ith zone

- office employment in the ith zone

- other employment in the ith zone

- retail employment in the ith zone

- model coefficients

Normalization

For each trip purpose (e.g. home to work trips), the number of trips originating at home must equal the number of trips destined for work. Two distinct models may give two

results. There are several techniques for dealing with this problem. One can either assume one model is correct and adjust the other, or split the difference.

It is necessary to ensure that the total number of trip origins equals the total number of trip destinations, since each trip interchange by definition must have two trip ends.

The rates developed for the home end are assumed to be most accurate,

The basic equation for normalization:

Sample Problems

Problem (Solution)

Variables

- Person trips originating in Zone i

- Person Trips destined for Zone j

- Normalized Person trips originating in Zone i

- Normalized Person Trips destined for Zone j

- Person trips generated at home end (typically morning origins, afternoon

destinations)

- Person trips generated at work end (typically afternoon origins, morning

destinations)

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Fundamentals of Transportation/Trip Generation

26

- Person trips generated at shop end

- Number of Households in Zone i

- office employment in the ith zone

- retail employment in the ith zone

- other employment in the ith zone

- model coefficients

Abbreviations

• H2W - Home to work

• W2H - Work to home

• W2O - Work to other

• O2W - Other to work

• H2O - Home to other

• O2H - Other to home

• O2O - Other to other

• HBO - Home based other (includes H2O, O2H)

• HBW - Home based work (H2W, W2H)

• NHB - Non-home based (O2W, W2O, O2O)

External Exercises

Use the ADAM software at the STREET website [1] and try Assignment #1 to learn how changes in analysis zone characteristics generate additional trips on the network.

End Notes

[1] http://street.umn.edu/

Further Reading

• Trip Generation article on wikipedia (http://en.wikipedia.org/wiki/Trip_generation)

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Fundamentals of Transportation/Trip Generation/Problem

27

Fundamentals of Transportation/Trip

Generation/Problem

Problem:

Planners have estimated the following models for the AM Peak Hour

Where:

= Person Trips Originating in Zone

= Person Trips Destined for Zone

= Number of Households in Zone

You are also given the following data

Data

Variable

Dakotopolis

New Fargo

10000

15000

8000

10000

3000

5000

2000

1500

A. What are the number of person trips originating in and destined for each city?

B. Normalize the number of person trips so that the number of person trip origins = the

number of person trip destinations. Assume the model for person trip origins is more

accurate.

Solution

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Fundamentals of Transportation/Trip Generation/Solution

28

Fundamentals of Transportation/Trip