Lecture 12 Flashcards
Definition of an intersection
An intersection is the area shared by 2 or more roads
Function of an intersection
the function of the intersection is to provide change for route direction
Intersections are of two types
AT grade intersection (requires traffic control system)
Grade separated or an interchange:
consists of structures to provide cross flow of the major traffic movements at different levels without interruption
Conflict points of an intersection
1-merging
2-weaving
3-diverging
4-crossing
potential conflict points for a 4 point intersection
are 32 look at page 11 and draw it
Why do we use traffic control
we use traffic control in order to reduce number of conflict points
Types of intersection control
1-)Yield signs
2-)stop signs
3-)intersection channelization
4-)traffic signals
Interchanges
grade separated intersections
Functions of interchange
1-) provide grade separation between two or more traffic arterials
2-) provide easy transfer of vehicles from one arterial to another
Warrants of an interchange ( When is an interchange needed)
1-)High traffic volumes
2-)reduction of bottlenecks and spot congestion
3-)road user benefits
4-)safety improvements
The configuration of an interchange depends on the following
1-)Site topography
2-)Traffic projections,(how the movements are at the intersection)
3-)land availability
4-)environmental impacts
first interchange type
Diamond interchange WE HAVE #DIAMOND INTERCHANGE 10 10 10 #TUDI TIGHT/COMPRESSED URBAN DIAMOND INTERCHANGE #DDI DIVERGING DIAMOND INTERCHANGE 8 8 2 #SINGLE POINT URBAN INTERCHANGE 8 8 8
When we use diamond interchange (responsible for drawing and conflict points)
we use diamond interchange when there is a freeway/non-freeway intersection
When we use diamond interchange, the flow on the freeway is uninterrupted
true
on the arterial of the diamond interchange we have four left turns
true
the diamond interchange is the less costly interchange
true
diamond interchange does not support heavy traffic on the surface street or on the ramps or on the left turns
true
what is the ramp function on the diamond interchange
the function of the ramp is to connect the freeway to the surface street also it functions as a transition from low speeds to freeway speeds
Diamond interchange variations
Tight/compressed urban diamond interchange (TUDI)
Used in urban areas where there is limited right-of-way
Diamond interchange variations
Double crossover/Diverging diamond interchange (DDI)
Drawing is required
The two directions of traffic on the non-freeway road cross to the opposite sides. Two signalized intersections with two phases each. Requires additional signage and pavement markings.
Diamond interchange variations.
Single point urban interchange (SPUI) .
Drawing is required.
Single signalized intersection that allows the two left turn movements to proceed simultaneously.
Second interchange type
drawing is required
Full cloverleaf interchange
Function of the full cloverleaf interchange
Allows non-stop full access between two busy roads.
In full cloverleaf interchange , the traffic merges and weaves but it doesnot cross at grade
true
the full cloverleaf interchange is typically used where a freeway intersects a busy surface street
true
Characteristics of full cloverleaf
# common interchange # Grade separation for intersecting roadways #All 8 turning movements are accomplished free of intersections with crossing traffic
Difficulties of full cloverleaf interchange
1) Requires large areas of land (land cost)
2) left turning vehicles execute 270 degrees right turn (sharp curve, steep grade)
3) we have weaving and merging at high speeds
4) weaving on main line results in reduced speed on main line
Weaving in a full directional cloverleaf
#Weaving occurs between the adjacent loops of a cloverleaf interchange (See picture) # The extent and impact of weaving depends on traffic volume, freeway number of lanes, distance between the ramps, and speed.
How we can eliminate the weaving
see picture
collector-distributor
weaving can be eliminated by adding a collector and distributor roads which divert entering or exiting traffic to these roads
How we can eliminate the weaving
see picture
directional ramps
we can remove weaving by replacing left turn loops with directional ramps which result in cloverstack interchange and total removal of weaving
THIRD interchange type is partial cloverleaf interchange,
drawing is required
functionally it is equivalent to a diamond and it is also known as a folded diamond where one or more ramps are folded into a loop on the opposite side of the surface street.
Partial cloverleaf interchange may have two ramps
True
In partial cloverleaf interchange loops can be placed in different quadrants to fit topography and traffic patterns.
true
fourth interchange type
directional interchange
#it is freeway to freeway interchange # accommodates heavy left turn movements by a 90 degrees turns to the left. # movements occurs at design speed of the expressway # reduce / eliminate weaving # it has higher number of required structures
Fifth interchange type
three leg intersection
Y-intersection
one grade separation
Sixth interchange type
T-intersection (trumpet intersection)
# it has three approaches # only one movement requires 270 degree turn, others are accomplished at 90 degrees.
Interchange selection considerations
#traffic forecasts #physical consideration (space, number of intersections..)) #Economical #SAFETY #Aesthetics # environmental impact
picture page 40 must memorize
See it
Name 4 assessments of interchanges
#level of service #Safety consideration # Delays at signalized intersections # Weaving, merging and diverging on the freeway.
page 42 memorize
true
look at pics from page 43 till end
true
