CE562 Lecture 13 Highway Functions

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CE562 Lecture 13 Highway Functions
Text A Policy on Geometric Design, p.1-14
(Chapter I)
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Classification of Highways

• Classification Criteria
• design types based on geometric features
  (freeways, other highways)
• route numbering (U.S., S.R., county road)
• character of service, function (arterials,
  collectors, local roads)

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Functional Classification

• It is not practical to provide direct-line
  connections between every potential
  origin-destination pair. Instead, trips must be
  channelized on a network of roads and streets.

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Functional Classification

• Arterial highways provide direct service for
  large number long-distance trips (between large
  towns, between residential and industrial areas
  within a large city, etc.)
• Local roads and streets provide service for a
  small number of trips along short distances
  (local traffic, access to high level highways)
• Collectors of an intermediate function connect
  local highways with arterial highways

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Your friends house
Termination (driveway)
Access (local)
Distribution (collector)
Main movement (arterial)
Collection (collector)
Access (local)
Your house
Origination (driveway)
Hierarchy of Movements and Roads
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Hierarchy of Movements and Roads

• Trip Phases
• origination (driveway)
• access (local road)
• collection (collector)
• transition (ramp)
• main movement (arterial highway)
• transition (ramp)
• distribution (collector)
• access (local road)
• termination (driveway)

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Access Needs and Controls

• Functions of roads
• access to property (local roads and streets)
• traffic mobility (arterial roads)
• dual function (collectors)
• A desirable access level is achieved by applying
  access control to arterial roads and sometimes to
  collectors

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Rural Roads

• Rural areas are outside of boundaries of urban
  areas.
• Rural principal arterial system
• Rural principal and minor arterial system
• Rural collector system
• Rural local road system

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• Rural principal arterial system has the following
  characteristics
• substantial part of traffic are statewide and
  interstate trips
• movements between urban areas with populations
  over 50,000 and majority of movements between
  areas with population over 25,000
• integrated connections within the system

2 - 4 of rural roads
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• Rural principal and minor arterial system has the
  following characteristics
• linkage of cities, larger towns, and other major
  traffic generators
• integrated interstate and inter-county system
• internal spacing consistent with population
  intensity
• trip lengths and volumes greater than those
  served by rural collectors and local system

6 - 12 of rural roads
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20 - 25 of rural roads

• Minor collector roads
• accumulate traffic from local roads
• serve locally important traffic generators
  (smaller communities)

• Major collector roads
• serve intra-county traffic generators
• link these places with larger towns or other
  routes of higher classification

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Rural local road system provides access to
abutting land, individual farms, etc.
65 - 75 of rural roads
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Urban Roads

• The boundaries of urban areas are set by
  authorized officials.
• Urban principal arterial system
• Urban minor arterial system
• Urban collector street system
• Urban local street system

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• Urban principal arterial system
• serves major movements within the urbanized areas
  
• integrated internally and connected with the
  rural principal arterial system
• includes interstate roads, other freeways,
  surface principal arterial streets with partial
  or no access

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• Urban minor arterial street system
• augments the urban principal system
• provides more access to the abutting areas (does
  not penetrate residential areas)
• carries bus routes
• spacing is between 0.2-5 km

15-25 of urban streets are arterials. They
carry 65-80 of traffic load.
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• Urban collector street system
• provides land access service
• circulates traffic in residential neighborhoods,
  commercial and industrial areas
• collects traffic from local streets
• carries local bus routes
• may form entire street grid in central business
  districts

5-10 of urban streets are collectors. They
carry 5-10 of traffic load.
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• Urban local street system
• permits direct access to abutting land
• discourages through traffic
• does not include bus routes

65-80 of urban streets are local. They carry
10-30 of traffic load.
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Integration of Planning and Design

• The planning process provides
• Functional classification of the future road
• AADT and design volumes
• Design speeds depend on the highway class
• arterials - high design speeds
• collectors - intermediate design speeds
• local roads - low design speeds
• The design speed and volume determine most of the
  highway design parameters.
• A freeway is an exception from the rule. It is
  not a functional class but has unique geometric
  criteria due to major differences in operations
  between this type of highway and surface
  arterials.