At grade intersections Flashcards
Describe the importance of road networks
Provides mobility
Traffic is a function of land use and vice versa.
3 functions of a network = movement,access and place
Describe the types of intersections at grade?
At grade = roads meet at same level
3 basic forms = not channelized and unflared, not channelized and flared and channelized (including roundabouts)
Describe unchannelised and unflared intersections
typically for the intersection between minor roads or when a minor meets a major
urban areas usually contain this type due to economic reasons, volumes of turning vehicle might requires some special treatment however.
Traffic is controled by signals or regulatory signage
Describe channelised and flared intersections
Flared: Auxiliary lanes = speed change lanes, passing lanes Channelized: paths of travel for various movements are separated and delineated using: a) Raised islands b) raised markers c) raised painted marking d) safety bars
Describe a roundabout
special type of channelized intersection where traffic moves clockwise around a central island and all movements are reduced to either merging or diverging
What is the aim of intersection design?
Improve traffic flow, reduce likelihood of consequence of crashes
done by controlling vehicle movements and reducing the number of points of conflict
What are the factors influencing design?
Traffic volume and characteristics Appropriate design vehicle topography economic constraints human factors crash history
What are the application of factors at intersection
People should not be surprised by the location of the intersection or layout
They should not be severely disadvantaged for making errors nor reward for deliberately committing unsafe actions
What are some key human factors
reaction times sight distance requirement gap acceptance behavior merge behavior crash risk and safety
What are the outcomes of considering human factors/
people aware of the intersection presence
aware of vehicles within and approaching the intersection
confidence in the ability to navigate the intersection safely
Encounters uniformity in traffic engineering and procedures
allows adequate reaction and decision time
Not severely disadvantaged for making errors
What are the advantages of the channelisation?
reduce general area of conflict by intersection at or near right angles
merge traffic streams at small angles
control speed by restricting width
provide a refugee for turning or crossing vehicles
prohibit certain turns
improve efficient and layout of signals
provide protection for pedestrians
improve alignment for all moments
provide locations for installing signals or regulatory signs
What are disadvantages for over channelisation?
Unwarranted obstructions
parking and access adjacent to intersection affected
cause problems for pavement maintenance and drainage
creates confusion
What are the 7 principles of intersection design
adequate visibility and sight distance when approaching and leaving
Reduction in relative speed between vehicles
reduction in the number of conflict points and separation of them
minimization of the conflict area
separation of the conflict points
preference to major traffic movements
definitions of paths
What are conflict points and what are they dependent on?
Intersection of vehicle paths, usually between major and minor road
depends on : number of approach, number of lanes
type of control , presence of channelization, movements allowed
how can we reduce conflict points?
realignment
reduced number of lanes and approach
changing control
deceleration of lanes
