Highway Functional Classification

Chapter 16

Dr. TALEB M. AL-ROUSAN

Highway Functional Classification Highways are classified according to their respective

functions in terms of the character of the service they are providing.

Primary Classification: Highways and streets are described as rural or urban roads.

Urban and rural areas have different characteristics (type of land and population density) which significantly influence travel patterns.

Second Level Classification for Urban and rural roads: Principal arterials (includes freeways) Minor arterials Major collectors Minor collectors Local roads and streets.

Functional System of Urban Roads Urban roads: all highway facilities within

urban areas. Urban areas: designated by state and local

officials, have population of (5000) or more. Urban areas divided into:

Urbanized areas (population > 50,000) Small urban areas (population 5000 – 50,000)

Urban roads are functionally classified into: principal arterials, minor arterials, collectors, and locals.

See Figure 16.1 for functional classes of suburban roads.

Urban Principal Arterial System Serves the major activity center of the urban area. Consists of the highest-traffic volume corridors. Carries most trips with origin or destination within

urban area. Serves trips by passing the CBD. All controlled-access facilities are within this system. Further divisions (subclasses) based on the type of

access to the facility:1. Interstate, with fully controlled access and grade

separation interchanges.2. Expressways, have controlled access but may include

at-grade intersections.3. Other principal arterials, with partial or no controlled

access.

Urban Minor Arterial System Streets and highways that interconnect

with the urban primary arterials. Serves trips of moderate length. Places more emphasis on land access than

primary arterial. Might serve local bus routes and connect

communities but do not go through neighborhoods.

Spacing is usually not less than 1 mile.

Urban Collector & Local Street System

Collector main purpose: collect traffic from local streets in the residential areas or in CBDs and convey it to the arterial system.

Local streets: all other streets within the urban area that are not included in the other three systems.

Local streets main purpose: to provide access to adjacent land and to the collector streets.

Through traffic is deliberately discouraged on local streets.

Functional System of Rural Roads

Rural roads are the highway facilities outside urban areas.

Rural roads are categorized as: principal arterials, minor arterials, major collectors, minor collectors, and locals.

See Figure 16.2 for functional classes of rural roads.

Rural Principal Arterial System Consists of network of highways that serve

most of interstate trips and part of intrastate trips.

Most of highway trips between urbanized areas and small urban areas are made on this system.

Subclasses: Freeways: divided highways with full controlled

access and no at-grade intersections. Other principal arterials: all principal arterials not

classified as freeways.

Rural Minor Arterial System

Augments the arterial system in the formation of a network of roads that connect cities, large towns, and other traffic generators (resorts).

Travel speeds are high as on the principal arterial system.

Rural Collector System

Carry traffic within individual counties Trip distances are shorter than those

on arterials. Major collectors: carry traffic to and from

county seats and large cities that not directly served by the arterial system.

Minor collectors: collect traffic from local roads and convey it to other facilities.

Rural Local Road System

All roads within the rural area not classified with the other systems.

Serves trips of relatively short distances

Connects adjacent lands with the collector roads.

Other Types of Roads According to jurisdictional responsibilities

(public works, municipalities). Freeways Main roads Secondary roads Collector roads Local roads Belt or ring roads Radial roads (passes through city center)

Primary Highway Classifications

UrbanRuralLand Expensive Land Cheaper

Access more important than speed

Speed more important than access

Pedestrian facilities needed (curbs, side walks, crossings)

Pedestrian facilities less needed, shoulders are more needed

Street lighting neededStreet lighting less or not needed

Loading & unloading

Trucks are not usually allowedTrucks allowed

LOS is low due to slow speed and high volumes

LOS is higher

More accidentsLess accidents

cyclingNo cycling

Types of Lanes Climbing lanes Escaping lane Acceleration lanes Deceleration lanes Turning (storage) lanes Parking (stopping) lanes Bus lanes Bicyclist lanes Overtaking lanes