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King Fahad University of petroleum & Minerals Civil Engineering Department . CE-576 Highway Geometric Design Chapter I Instructor: Dr. Nedal T. Ratrout . Chapter I. Highway Functions. Scope:.

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king fahad university of petroleum minerals civil engineering department

King Fahad University of petroleum & MineralsCivil Engineering Department


Highway Geometric Design

Chapter I

Instructor: Dr. Nedal T. Ratrout

chapter i

Chapter I

Highway Functions



Introduce the concepts needed for understanding the functional classification system of highways functions

  • Systems & Classifications.
  • Hierarchies of Movements and components.
  • Functional Relationships.
  • Access Needs & Controls.
  • Definitions of Urban & Rural Areas.
  • Functional Systems for Rural Areas.
  • Functional Highways Systems for Urbanized Areas.
  • Functional Classification and Design Type.
  • Summary.
types of classifications
Types of classifications:
  • Classification by design type

Based on geometric features (e.g.freeways and highways).

  • Classification by route numbering

(e.g.,U.S., state, county), this classification is helpful for traffic operations.

types of classifications8
Types of classifications:
  • Administrative Classification

(e.g.,National highway system, Non-national highway system), used to denote government responsibility & method of financing

  • Functional Classification

Grouping of highways by the character of service they provide, it’s developed for transportation planning & design process

a typical trip includes six stages arranged from higher to lower based on traffic volume
A typical trip includes six stages arranged from higher to lower based on traffic volume:
  • Main Movement
  • Transition
  • Distributor
  • Collectors
  • Local Access
  • Parking
Based on traffic generation intensity sometimes it’s desirable to delete intermediate facilities.
  • Each element of the functional hierarchy can serve as collector facility for the higher element.
  • By defining the spacing needs & traffic volume demands, it’s possible to determine which cases should use full system & in which cases intermediate elements maybe bypassed.
The arterial highways generally provide direct service between cities & large towns.
  • Collectors serve small towns directly & connecting them to the arterial network & collect traffic from the local roads or distribute traffic to the local roads
  • Local roads serve individual farms and other rural land uses.
Highways & streets network must provide access property & travel mobility.
  • Local Rural facilities provide land access function.
  • Arterial streets provide mobility.
  • Collectors offer balanced service for both functions.
Urban areas are the areas have population between 5000 to 50,000.
  • Rural areas are those areas outside boundaries of urban areas.
urban rural areas have different characteristics with regard to
Urban & Rural areas have different characteristics with regard to:
  • Density & type of local use.
  • Density of street & highway networks.
  • Nature of travel patterns.
  • Rural include more arterials (principal & minor) but urban include more collectors & subdivisions of collectors.
rural principal arterial system
Rural Principal Arterial System:
  • Corridor movement with trip length & density suitable for substantial statewide or interstate travel.
  • Movements between urban areas.
  • Integrated movement without stub connection except unusual geographic or traffic flow dictate.
rural minor arterial system
Rural Minor Arterial System:
  • Linkage of cities, large towns and other traffic generators.
  • Integrated interstate & intercounty service.
  • Internal spacing consistent with population density.
  • Corridor movement consistent with items 1 trough 3 with trip length & travel densities greater than those served by rural collector or local system.
rural collector system major collector roads
Rural Collector SystemMajor Collector Roads:
  • Serve small towns & other traffic generators such as shipping points, mining & agricultural areas.
  • Link theses places with nearby larger towns or cities or with routs of higher classifications.
  • Serve more important travel corridors.
rural collector system minor collector roads
Rural Collector SystemMinor Collector Roads:
  • Spaced at intervals consistent with population density to accumulate traffic from local roads.
  • Provide service to small communities.
  • Link locally important traffic generators with major collectors.
rural local road system
Rural Local Road System:
  • Provide access to the lands and link them with the collectors.
  • Serve travel with short distance.
urban principal arterial system
Urban Principal Arterial System:
  • Serves major centers of activity, the higher traffic volume & long trips
  • Carries most of trips entering & leaving the urban area & trips between major inner-city communities.
  • Provides continuity for all rural arterials that intercept the urban boundary.
urban principal arterial system31
Urban Principal Arterial System:

4. Spacing Between principal arterials vary from 1.6 km [1mi] to 8 km [5mi]

5. Emphasis on offering high mobility.

urban minor arterial system
Urban Minor Arterial System:
  • Serves trips of moderate length & distributes travels to small areas & cities.
  • Emphasis on offering land access and lower mobility.
  • Provide urban connection to rural collector roads.
Spacing from 0.2to1.0km [0.1to0.5mi] to 3to5km [2to3mi], not more than 2km [1mi] in fully developed areas.
  • May carry local bus routs.
urban collector street system
Urban Collector Street System:
  • Provides both mobility & land access.
  • Penetrates residential areas.
  • Distributes trips from arterial system to the local streets & collects traffic from residential areas & channels it into the arterial system.
  • May carry local bus routs.
urban local street system
Urban Local Street System:
  • Permits direct access to the lands.
  • Offers lowest level of mobility.
  • Contains no bus routs.
two major problems arise from using functional classification system as a design type of highways
Two major problems arise from using functional classification system as a design type of highways
  • Freeway is normally classified as principal arterial while it has unique geometric criteria that need design designation apart from other arterials.
Geometric design criteria & capacity levels have been based on traffic volume ranges, highways with comparable traffic volume provide identical level of service, although there maybe considerable difference in the function they serve.
Definition of the function of the facility helps the designer to determine the level of service to fulfill this function & then to select design speed and geometric criteria.
  • The functional concept is important in highway planning & design, it’s integrate highway planning & design process.
chapter ii

Chapter II

Design Controls & Criteria



Discuss the characteristics of vehicles that act as criteria for the optimization or improvement in design of highways.


Design Vehicles:

  • General Characteristics
  • Minimum Turning Paths of Design Vehicle
  • Vehicle Performance
  • Vehicular Pollution
classes of design vehicles
Classes of Design Vehicles
  • Passenger Cars

Include passenger cars of all sizes, sport, minivans, vans & pick-up trucks.

2. Buses

Include intercity, city transit, school & articulation buses.

3. Trucks

Include single-unit trucks, truck tractor-semitrailer combinations, truck tractor with semitrailer in combination with full trailer.

. Recreational vehicles

Include motor homes, cars with camper trailers, cars with boat trailer, motor homes with boat trailers, and motor homes pulling cars.

  • Note: Bicycles must be considered as a design vehicle because it’s allowed to used on highways.
Physical characteristics & proportions of vehicles using highway are the key controls in geometric design (e,g., weight, dimensions, & operating characteristics)
  • In geometric design, designer should consider the largest design vehicle that will use the facility.
when we select design vehicle we have to consider the following
When we select design vehicle we have to consider the following:
  • Select passenger car when the main traffic generator is a parking lot or service of parking lots.
  • Select single-unit truck for intersection design of residential streets & park roads.
  • Select city transit bus in the design of state highway intersections with city streets that have few large truck using them.
Small bus is selected in the design of small streets intersections.
  • Select WB-20 [WB65 or 67] truck as a minimum size design vehicle for intersections of freeway ramp terminals with arterial crossroads and intersections state highway and industrialized street.
The boundaries of the turning path of each design vehicle established by the outer trace of the front overhang & the path of the inner rear wheel. Outer front wheel follows the circular arc defining the minimum centerline turning radius (CTR).
  • Effects of driver characteristics & effects of slip angle of wheels are minimized by assuming the speed of vehicle for the min. turning radius is less than 15km/h [10 mph]. For higher speed we need larger turning radius.
Trucks & buses have longer wheel bases & greater min. turning radii than passenger cars. Single-unit trucks & buses have smaller min. turning radii than most combination vehicles.
Acceleration & deceleration rates of vehicles are often critical parameters in determining highway design.
  • Based on acceleration & deceleration performance passenger cars seldom controls design, lower performance vehicles are suitable for design application such as loaded truck or bus or low powered car.
The highway designer should consider the following sources of pollution in selecting appropriate transportation alternatives
  • Pollutants emitted from motor vehicle
  • Noise pollution
factors affect the rate of pollutant emission from vehicles
Factors affect the rate of pollutant emission from vehicles:
  • Vehicle mix
  • Vehicle speed
  • Ambient air temperature
  • Percentage of vehicles operating in cold mode
  • Vehicle age distribution
noise pollution is generated by
Noise pollution is generated by:
  • Mechanical operation of the vehicle & its equipment
  • Vehicles aerodynamics
  • Action of vehicle’s tires on the pavement
  • Sounds of brake
  • Exhaust backfires
  • Horns
  • Sirens of emergency vehicles
For passenger cars noise is principally produced by the tire-road interaction with some wind noise, but for condition of max. acceleration, the engine system noise is predominant.
  • For trucks noise is produced from exhaust, engine gears, fans, air intake, steep grades (cause an increase in noise for large trucks), and tire-roadway interaction with wind noise. For trucks, engine exhaust noise dominate tire-roadway interaction for most operating conditions.