Classification of Urban Streets - Transportation Engineering - Lecture Slides, Slides for Transportation Engineering. Allahabad University
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amar15 May 2013

Classification of Urban Streets - Transportation Engineering - Lecture Slides, Slides for Transportation Engineering. Allahabad University

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Some concept of Transportation Engineering are Basic Transportation Model, Classification of Urban Streets, Example of Shock Wave, Geometric Design of Highways, Route Choice, Trip Assignment, Time-Distance Diagrams. Main...
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Classification of Urban Streets for Design

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Classification of Streets and Highways for Design

The classification system is fundamental to the highway design process.

In essence, the classification system is the framework for describing the type of roadway that can be built as part of a given design code. The classification feature determines issues such as appropriate speed, the types of components needed and the size of these components.

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Functional Classification The AASHTO Approach

• The AASHTO design is the most prevalent approach to design in USA over the

last 60 or 70 years

• AASHTO based on FUNCTIONAL CLASSIFICATION OF HIGHWAYS

• Function Classification is used to determine Design Speed and Roadway Type

• Under AASHTO, roads are classified as Arterials, Collectors and Locals

• Land uses are also divided into Rural and Urban

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Functional Classification Land use

Facility Type

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Functional Classification The AASHTO Approach

• For function classification roads are grouped according to the type of

function they are intended to provide

• Main difference is based on the degree to which the road is designed to provide Access or Mobility

• The definition of the types of roads which make up the functional

categories varies depending on whether the system is in a rural or urban area. The definition of types of roads for urban areas are given next.

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Functional Classification The AASHTO Approach

Urban Areas Principal Arterials - high volumes, long trip length • Minor Arterials -moderate trip length • Collectors - trips serving neighborhoods by collecting traffic from local streets • Local - roads that are primarily for providing access to properties

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AASHTO Street Hierarchy

The underlying assumption of functional classification is that we are creating a hierarchical street network Docsity.com

Mobility and Access

Mobility

Access

High Access - Little Mobility

Low Access - High Mobility

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Objections to AASHTO Functional Classification

Four of the main problems are summarized as follows:

1. Based on Hierarchical Network: AASHTO is based on the hierarchical street network. It should not be applied in designing connected urban street networks.

2. Poor Description of Land Use Type: The AASHTO functional classification defines land use as either rural or urban. In order to better understand the land use context we need a finer grained description of land use context.

3. Poor Description of Facility Type: The terms arterial, collect and local do not tell the designer enough about the specific design characteristics of the road.

4. No Guide to Facility/Land Use Compatibility: The AASHTO method of classification gives no guidance to the designers as to what type of facility is appropriate for a given context.

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Objections to AASHTO Functional Classification

1. Based on Hierarchical Network: AASHTO is based on the hierarchical street

network. It should not be applied in designing connected urban street networks.

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Evolving Street Network

Adapted from Stephen Marshall

Pre-1950’s Post-1950’s AASHTO Network

Severe Congestion Urban Network

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Objections to AASHTO Functional Classification

2. Poor Description of Land Use Type: The AASHTO functional classification defines

land use as either rural or urban. In order to better understand the land use context we need a finer grained description of land use context.

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Functional Classification Land use

Facility Type

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Objections to AASHTO Functional Classification

3. Poor Description of Facility Type: The terms arterial, collect and local do not tell the

designer enough about the specific design characteristics of the road.

For example, Route 44 and Route 195 (in downtown Storrs) are both

collectors but they have very different design. Route 44 has shoulders, guide rails and side slopes while Route 195 has no shoulders but has curbs and sidewalks. A good method of classification for design should have a clear way of distinguishing between these two types of design so that designers can select the right road for the right land use context.

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Objections to AASHTO Functional Classification

4. No Guide to Facility/Land Use Compatibility: The AASHTO method of

classification gives no guidance to the designers as to what type of facility is appropriate for a given context.

The most egregious example of facility type not matching or being suitable for the land use are freeways in cities

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Institute for Transportation Engineers/Congress for the New Urbanism Urban Street Classification

The Institute for Transportation

Engineers and the Congress for the New Urbanism (along with the Federal Highway Administration and the US EPA) recently released a new method of classification that addresses some of these issues.

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Institute for Transportation Engineers/Congress for the New Urbanism Urban Street Classification

The ITE/CNU approach is based on the following: 1. Urban Networks: Is is explicitly based on a connected urban network of

streets 2. Land Use: Context Zones is used to characterizing the land use types 3. Facility Type: Thoroughfare types is used to characterize the facility type

for design 4. Land use/Facility Type Compatibility: It explicitly Define Compatibility of

Context Zone and Thoroughfare Type

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Institute for Transportation Engineers/Congress for the New Urbanism Urban Street Classification

Land use Characterize by the Transect Characterize the land use types into six categories from the most rural T1 to

the most urban T6.

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Institute for Transportation Engineers/Congress for the New Urbanism Urban Street Classification

Thoroughfare Types and Compatibility Rural Urban Freeway X Expressway X Highway X Road X Boulevard X Avenue X Streets X Lanes X Alleys X Mews X

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Institute for Transportation Engineers/Congress for the New Urbanism Urban Street Classification

Some Differences between Roads and Streets • Roads typically have shoulders, side slopes, open drainage, guide rails

• Streets typically have no shoulders, side slopes, open drainage or guide

rails …. Conversely, streets do have curb, roadside with cultivated trees, sidewalks, buildings up to sidewalk

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