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8 MODULE 8: TRANSPORTATION IMPACT ASSESSMENT

8.1 Definition

Transportation impact assessment (TIA) is an evaluation of the potential effects that a particular
development’s traffic will have on the transportation network in its impact area. Previously, called
traffic impact assessment, ‘traffic’ was changed to ‘transportation’ to represent a wider coverage of
the transportation system rather than be limited to traffic as implied. The magnitude of studies will
vary depending on the following:

• Type of development, which may refer to residential, commercial, industrial, recreational,

institutional or other as well as mixed;
• Size or density of development, which may refer to high, medium or low density of
development; and
• Location of development, which may generally refer to the central business district or city
center, suburb, rural area

8.2 Usefulness

How is a TIA useful? It generally answers or attempts to answer the following questions pertaining
to a proposed development or project:

1) What are the transportation improvements needed to serve the traffic generated by the new
development?
2) How much will the improvement cost be and who will pay for them?
3) Will the new project have impact on traffic on any existing residential streets and how will
those impacts be mitigated?
4) Will the new development aggravate any existing safety hazards or create new ones and,
if so, how can those hazards be corrected?
5) Can the proposed development be served by public transportation?
6) Is the design of the development friendly towards bicyclists and pedestrians who need to
access the development or who need to pass through or by the development?
7) Is the on-site parking sufficient or is there an opportunity to share parking with other
adjacent uses?
8) How many driveways are needed, what design should each driveway have and is there a
long enough throat for each driveway that is clear of parking spaces and other cross aisle
traffic?
9) If any driveway is proposed to be signalized, is the traffic signal really needed and can on-
site circulation handle the traffic that will be queuing to wait for a green light?

8.3 Applications of TIA

ATIA is typically employed in situations when there is a proposed development that is perceived to
generate trips that will have a significant impact on transportation. The National Center for
Transportation Studies (NCTS) identified the following situations:

• When a specified amount of area is being rezoned.

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Based on international studies, speed has serious consequences when a pedestrian is involved.
Faster speeds also increase the likelihood of a pedestrian being hit since motorists are less likely
to see and react to a pedestrian and are even less likely to be able to stop in time to avoid hitting
one.

Figure 9.7 shows that even at the speed of 30kph, there is about 5% chance pedestrian’s death
if hit by a motor vehicle. At 60kph, that probability of fatal crash is about 90%.

Source: U.K. Dept of Transport

Figure 9.7: Pedestrian’s chance of death if hit by a motor vehicle

9.2 Road Safety Action Plans

Since 2005, the Philippine government has crafted its own National road Safety Action Plans, the
first one was in 2005 as part of the ADB – ASEAN Regional Road Safety Program; the second one
was in response to the call of UN for a decade of action on road safety from 2011 to 2020; the third
one was an update to this plan for the period 2017 – 2022.

Source: Sigua, R.G.

Figure 9.8: Philippine Road Safety Action Plans

9.2.1 The Safe System Approach

The Philippine Road Safety Action Plan (PRSAP) 2017-2022 provides a long-term vision for the

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improvement of road safety in the Philippines based on the Safe System approach and a Vision
Zero, which envisions a Philippine Society with zero deaths on the road.

Guiding Principles:
• People make mistakes.
People will commit errors on the road, but these should not lead to death or injury.
• People are vulnerable. There is a limit to the impact that the human body can tolerate.

• Road safety is a shared responsibility. Those who design the roads and those who use
the roads are both responsible in preventing road crash deaths or injuries from
happening.

• All parts of the system must be strengthened. Even if one part fails, the road user must be
still protected.

The road system is designed to anticipate and accommodate human error and is based on the
vulnerability of the human body.

Four Core Safe System Pillars:

• Safe road users who are competent and follow traffic laws;

• Safe vehicles that have technology to help prevent crashes and safety features that
protect road users in the event of a crash;

• Safe roads that are self-explaining and forgiving of mistakes to reduce the risk of crashes
occurring and to protect road users from fatal or serious injury should a crash occur;

• Safe vehicle speeds that suit the function and the level of safety of the road to ensure that
crash forces are kept below the limits that cause death or serious injury.

Source: PRSAP 2017

Figure 9.9: Safe system 4 pillars

9.2.2 Strategies for improving road safety for specific vulnerable road users

This section discusses the different strategies in improving the road safety of vulnerable road users.
Table 9.5 is intended for pedestrians. Depending on the extent of challenges facing the pedestrians,
strategies are listed to meet the four key objectives. It may be observed that the strategies revolve
around the 3 ‘E’s, namely, engineering, enforcement, and education.

a. Improving Pedestrian Safety

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Table 9.5: Strategies for improving road safety of pedestrians

Source: Sigua, R.G.

Exclusive phase for pedestrians

Aside from allowing pedestrians to move simultaneously with the vehicular traffic, the provision of
‘scramble’ phase can offer more level of safety to pedestrians. During this phase, vehicles in all
directions are required to stop to allow pedestrians to cross in all directions, including diagonally.

Figure 9.10: Scramble Phase for pedestrians

Pedestrian footbridges

Pedestrian overpass(footbridge) or underpass is oftentimes in the list of recommendations to

separate/eliminate conflicts between pedestrian and vehicular traffic. However, such
structure/facility creates difficulties to the physically challenged pedestrians.

Photo taken by author

Figure 9.11: Pedestrian footbridge

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Table 9.7: Audit Criteria based on DPWH Road Safety Audit Manual (2004)

Source: DPWH.

Qualifications of Road Safety Auditors based on the DPWH Road Safety Audit Manual
RSA must be performed by a team of people who have sufficient experience and expertise in the
areas of road safety engineering, accident investigation and prevention, traffic engineering and
road design. Having a team offers the following advantages:
• Diverse backgrounds and different experience of people in the team;

• Cross fertilization of ideas which can result from discussions; and

• Advantages of having more knowledge available.
Successful Road Safety Auditor must have experience in road safety engineering and an aptitude
for road crash investigation and prevention techniques.
The experience of a Road Safety Auditor should also be linked with an understanding of:
• Traffic engineering and traffic management;
• Road design and construction techniques; and
• Road user behavior
At present, these requirements of the DPWH Road Safety Audit Manual cannot be fulfilled due to
a lack of qualified (internal and external) experts. There is therefore a need for more RSA
practitioners at the DPWH in charge of national roads; at the local government units in charge of
local roads; and in corporations/agencies operating the expressways.

Road crash reduction

Figure 9.14 shows the general process flow of conducting blackspot studies.

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Source: Sigua, R.G.

Figure 9.14: General process flow of conducting blackspot studies

Blackspot Definition

The current DPWH Accident Blackspot Investigation Handbook (2004) has the following criteria for
identifying blackspots for road sections:

“Average of 3 major accidents per year per kilometer of road length over the past 2 to 3 years”

For intersections or short segments of 500 meters, the same number of accidents/road crashes is
used.
The Handbook was used in conjunction with the Traffic Accident Recording and Analysis System
(TARAS) Database.

9.3 Funding and Support for Road Safety

The last key area is funding and support for road safety. Road safety is only one of the many
competing demands for our scarce resources, but it is essential that it is not overlooked in
developing plans and policies. Road safety is everyone’s responsibility, and it is not enough to rely
on the government alone. It is important to tap the resources of the private sector as well.

9.4 Assessment of Road Safety

The state of road safety of a country or a region is normally gauged by the frequency of occurrence
of accidents. Key indicators are number of accidents (fatal, injured, or property damage) and
accident rates. The rates are normally used instead of actual numbers for comparison studies.

This section provides discussion on some tools to assess road safety situation of an area or region,
as well as specific locations such as intersections or road sections.

Accident rate per 100,000 population

One measure of accident rate is per 100,000 population like the one utilized in the health sector.
For instance, if a certain town, city, or region has N accident occurrences in 1 year and has a
population P, then:
Ap = 根100,000

The following figures and table show such rates are used for the purpose of comparing road safety

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situations.

Source: WHO

Figure 9.15. World fatality rates

Source: PSA, 2017

Figure 9.16: Number of road deaths and death rate per 100,000 population

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Table 9.8. Fatality rates in ASEAN and selected countries (2013)

Source: WHO

Accident per registered vehicles

Another measure of accident rate is per 10,000 registered vehicles. Again, if there are N accidents
in one year and the number of registered vehicles for the same year is V, then:
Av = 根10,000

For specific locations, such as intersections or road segments, the following rates may be utilized:

Accident Rates for Intersections

When analyzing traffic accidents at intersections, the total entering traffic volume usually in AADT
is considered. The equation below is used to compute the accident rate per million entering vehicles
(mev). The factor of 1,000,000 is applied for convenience to obtain values of Ai within 2 to 3 digits.

1,000,000 根 N
Ai =
365 根 T 根V

where: N – total number of accidents in time T

T – time frame of analysis, year
V – AADT or annual average daily traffic

Road Crash Rates for Road Sections

For segments of highways, accident rates are computed based on total vehicle-kilometers of travel.
The equation below is used to compute the accident rate per 100 million vehicle-kilometer (mvk).
Again, the factor of 100 million is applied for convenience.

100,000,000 根 N
As =
365 根 T 根V 根 L

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where: N – total number of accidents in time T

T – time frame of analysis, year
V – AADT or annual average daily traffic
L – length of section in km.

9.5 Identifying hazardous locations or blackspots

There are several methods of identifying blackspots or hazardous locations. Two methods will be
discussed based on statistical analysis.

Classic Statistical Method

The method assumes that the number of accidents at locations of interest follows a standard normal
probability distribution. The method flags a location as hazardous if it satisfies the following
inequality:

Xi > X + K 根 S
where: Xi - accident frequency or rate at location i
X - mean frequency or rate for all locations under consideration
K – constant corresponding to a certain level of confidence
S – sample standard deviation for all locations.

Table 9.9 provides a guide on the appropriate values of K for a given level of confidence.

Table 9.9: Commonly used levels of confidence and K values.

Level of K values
Confidence, %
90 1.282
95 1.645
99 2.327

Rate Quality Control Method

This is a variation of the classic statistical method. Instead of a normal distribution, the method
assumes that the number of accidents at a set of locations follows a Poisson distribution. Also, the
method applies only to rates and not frequencies. It compares the rate of a particular location to
the mean rate at similar locations rather than at all locations.

The method flags a location as hazardous if it satisfies the following inequality:

( Y )0.5 1
Yi > Y + K 根||（ )|| +
Vi 2Vi

where: Yi - accident rate observed at location i

Y – mean accident rate for all locations with characteristics
similar to those of location i
V – volume of traffic at location I, in the same units as the
accident rates are given
K – same as in classic method

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9.6 The Role of Enforcement in Road Safety

Based on WHO report, the following have been identified as key risk factors (Source: Road Safety:
Basic Facts, WHO)
Motorcycle helmets
Seatbelts
Drink & driving
Speed
Child restraints
Mobile phones

Some of the facts are enumerated based on the effects of the above-mentioned key risk factors:
• Drinking and driving, with BAC level of over 0.05 g/dl greatly increases the risk of a crash
and the possibility that it will result in death or serious injury.

• Wearing a seatbelt can reduce fatalities among front-seat passengers by up to 50% and
among rear-seat car passengers by up to 75%.

• Wearing a standard motorcycle helmet correctly can reduce the risk of death by almost
40% and the risk of severe injury by over 70%.

• Child restraint systems decrease the risk of death in a crash by about 70% for infants and
up to 80% for small children.

• In high income countries, speed contributes to about 30% of road deaths, while in some
low- and middle-income countries speed is the main factor in about half of road deaths.

Based on studies in different countries, enforcement has shown to be very effective in addressing
the key risk factors.
• Drinking and driving: enforcement through random breath-testing checkpoints is highly
cost-effective and can reduce alcohol-related crashes by approximately 20%.
• When helmet laws are enforced, helmet-wearing rates can increase to over 90%.

• Public awareness campaigns, mandatory seatbelt laws and their enforcement have been
highly effective in increasing the rates of seatbelt wearing.

• Mandatory child restraint laws and enforcement are effective in increasing the use of child
restraints.
When planning for an awareness campaign or for stricter enforcing of the lawas part of the activities
of a safety program, Table 9.10 provides information which may help in the preparation prior to
implementation.

Table 9.10: Preparation prior to implementation.

Source: Sigua, R.G.

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Post assessment is necessary to determine whether measures introduced are effective. For
instance, compliance rate must increase; the number of apprehensions must decrease; and overall,
the number of road crashes by severity must also decrease.

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10 MODULE 10: TRANSPORTATION PLANNING CONCEPTS

Module 10 consists of 3 parts. In the first part, we will discuss key ideas on transportation planning
including the nature of urban transportation problems and the need to conduct responsive
transportation planning in order to achieve sustainable transportation.

In the succeeding sections, we will cover key concepts and standard practices in travel demand
forecasting and review the tools and techniques currently employed in the application of the so-
called Four-Step Model which is a standard approach and methodology in the conduct of travel
demand forecasting.

10.1 Challenges facing Urban Transport

First, we need to understand the fundamental challenges that cities face in terms of urban
transportation. Cities have high concentrations of economic activities and hence need to be
supported by transport systems in order for these economic engines to work efficiently and
effectively. We need to realize that urban transport problems arise when there is poor urban
circulation. It is also important to recognize that there is a growing complexity of cities for which the
transport system needs to address increasingly.

Key urban transport problems include the following:

1. Traffic congestion and parking difficulties – this is the most prevalent transport problem and
is linked with the diffusion of the automobile
2. Public transport inadequacy – many public transport systems are either over or under used
with both cases creating problems of crowdedness on the one hand and low patronage on
the other
3. Difficulties for pedestrians – intense circulation and the lack of consideration of pedestrian
movements create serious problems in cities
4. Environmental impacts and energy consumption – pollution has greatly lowered the quality
of life in urban areas and dependence on petroleum has
5. Loss of public space – the construction of roads for vehicle as well as large-scale mall
developments have greatly reduced available green space for parks and open spaces
6. Accidents and safety - growing circulation in urban areas has been linked with a growing
number of accidents and fatalities
7. Land consumption - over-reliance on some forms of urban transportation can lead to
wasteful use of limited land area

We can relate car and public transport through a vicious cycle where an increase in car ownership
leads to reduced demand for public transport as depicted in Figure 1. Car dependence is a critical
issue that we must address in the context of Metro Manila and other key cities. In fact, the use of
personal mobility has extended to the alarming increase in the use of motorcycles.

Figure 10.1. Car and Public Transport Vicious Cycle

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We can also appreciate the negative impact of over-reliance on road building in the famous black
hole theory of road investment. The right perspective is not to dismiss the role of road investments
per see but to situate road infrastructure as part of a holistic strategy to curb car dependence and
promote use of public transport systems.

Figure 10.2: Black Hole Theory of Road Investment

We should understand the land use and transport systems are inter-connected. Transport systems
affect traffic conditions which in turn affect the land use system. On the other hand, land uses give
rise to trip generation that utilize the transport system. We can simulate changes in the transport
sector, for example, an improvement in the transport network. On the other hand, we can simulate
changes in the land use sector, perhaps through a land development project from a subdivision or
even a condominium development.

Figure 10.3: Land use and Transport Interaction

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Figure 10.4: Changes in the Transport System

Figure 10.4: Changes in the Land Use System

The challenges in integrating land use and transport are:

a) Weak integration of the social dimensions of urban planning in existing systems;
b) Weak coordination mechanisms among local governments and the higher planning
authorities
• Effective land use planning has two components: long term comprehensive planning to
deal with metropolitan scale issues and site or locality specific plans.
c) Lack of integrated planning models that are capable of addressing air pollution, transport
and health issues as decision-support tools for a comprehensive planning process.
• There is a need for good data but also for models that are not overly data-hungry.
• Scope for development of ‘sketch planning’ methods
d) Lack of effective urban development management is required to manage the
implementation of land use/ transport plans and policies.
• Significant technical capacity, preferably at a local level, is required to provide
responsive urban management.
e) Lack of timely provision of infrastructure
• Transport is a useful instrument for structuring land uses within an appropriate planning
framework.

In rejecting the former paradigm of building capacity, transport planners have turned increasingly
to managing both demand and the transport system. Building roads has produced a car-oriented
society in which the other modal alternatives have little opportunity to co-exist. Car ownership is
beyond the ability of the transport planner to control directly and the question remains if it should.
But car use and ownership is affected by land use and density, both elements that planners can
affect. High population densities, in particular, favor walking, bicycling and public transit use.

Managing the demand for travel is made up of a large number of small interventions that
cumulatively can have impact of car use, but in particular improve the livability of cities. A sample
of well-practiced and successful interventions includes:

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• Park and ride

• Traffic calming
• Priority lanes for buses, and high-occupancy vehicles
• Alternate work schedules
• Promoting bicycle use
• Car sharing
• Enhancing pedestrian areas
• Improving public transit
• Parking management

According to the Brundtland Commission, Sustainable Development is ”Development which meets

the needs of the present without compromising the ability of future generations to meet their own
needs“. As such, a sustainable city must offer to its population a suitable urban environment,
employment, food, housing and transportation without compromising the welfare of the future
population of that city.

As transport planners and engineers, we should actively pursue sustainable transport in our
respective practice and spheres of influence. Based on the vision of sustainable development, we
envision cities that provide a suitable urban environment including transportation systems that meet
the needs of the present population without compromising the welfare of future generations. There
are 3 dimensions of sustainability that we should be concerned about:
There are 3 dimensions of sustainability that we should be concerned about:
• Intergenerational equity
• Social equity
• Spatial responsibility

Figure 10.5: Sustainable Transport

Another effective way of visualizing the interdependencies among various land use and transport
factors is through systems dynamics where negative feedback (‘vicious cycle’) and positive
feedback (‘virtuous cycle) loops are identified and evaluated.

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Figure 10.6: Dynamics of Urban Transportation

Travel Demand

Travel demand occurs as a result of thousands of individual travelers making individual decisions
on how, where and when to travel. These decisions are affected by many factors such as family
situations, characteristics of the person making the trip, and the choices (destination, route and
mode) available for the trip. Travel demand models refer to a series of mathematical equations that
are used to represent how choices are made when people travel.

Models are important because transportation plans and investments are based on what the models
say about future travel. Models are used to estimate the number of trips that will be made on a
transportation systems alternative at some future date. These estimates are the basis for
transportation plans and are used in major investment analysis, environmental impact statements
and in setting priorities for investments.

10.2 Transportation Planning

Transportation Planning is the functional area within transportation engineering that deals with the
relationship of land use to travel patterns and travel demands The planning, evaluation, and
programming of transportation facilities, including roadways, transit terminals, parking, pedestrian
facilities, bikeways, and goods movement.

The objectives of transportation planning are:

• Improve coordination between land use and transportation systems
• Provide cooperative interaction between planning, design, and operation of transportation
services
• Maintain a balance between transportation-related energy use and clean air
• Encourage alternative modes of transportation that enhance energy efficiency while
providing high levels of mobility and safety

Transportation planning at various levels should be aligned and harmonized to ensure consistency
and complementarity of strategies.

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Figure 10.7: Alignment of Various Transportation Plans

There are seven (7) steps involved in functional transportation planning, namely:
1) Goals and Objectives
2) Inventories
3) Forecasts
4) Network Planning
5) Analysis of Alternatives
6) Evaluation
7) Selection/ Implementation

Figure 10.8: Functional Transportation Planning Step 1 - Goals and Objectives

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Figure 10.9: Functional Transportation Planning Step 2 - Inventories

Figure 10.10: Functional Transportation Planning Step 3 - Forecasts

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Figure 10.11: Functional Transportation Planning Step 4 - Network Planning

Figure 10.12: Functional Transportation Planning Step 5 - Analysis of Alternatives

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Figure 10.13: Functional Transportation Planning Step 6 – Evaluation

Figure 10.14: Functional Transportation Planning Step 7 – Selection/ Implementation

10.3 Travel Demand Forecasting

Travel Demand Forecasting is a multi-stage process, and there are several different techniques
that can be used at each stage. The basic steps are as follows:
1) Database Development
2) Trip Generation
3) Trip Distribution
4) Modal Split
5) Traffic Assignment

A Trip is a one-way movement from a point of origin to a point of destination. Home-based trips are
trips that either start from or end at the home. Trips from home to work are referred to as Home-
Based Work (HBW) trips. Trips from home to school are referred to as Home-Based School (HBS)
trips. Other types of trips coming from home are referred to as Home-Based Others (HBO). Finally,
trips that do not have home as its origin or destination are referred to as Non-Home Based (NHB)
trips.

Figure 10.15: Definition of a Trip

Trips captured in the conduct of Household Interview Surveys (HIS) can be classified based on:
• By Purpose (Work, School, Shop, Others)
• By Time of Day (AM, PM, peak, off-peak)

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