TRANSPO TERMS
It refers to establishment of horizontal and vertical alignments and cross section, based on considerations such as operating characteristics of vehicles, design standards, and drainage.
Geometric design
It is the distance required to see an object 0.15 m high on the roadway.
stopping sight distance
It is the distance required to see an oncoming vehicle of a certain minimum size
passing sight distance
It is defined as the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern.
design speed
Reaction times vary widely. As a result, the usual practice is to use a single, rather conservative value. AASHTO suggests a value of in its Policy on Geometric Design of Highways and Streets.
2.5 s
It refers to drawings, usually accompanied by notes, of various aspects or components of the design.
plans
These are written instructions detailing how the facility is to be constructed.
specifications
It include cost estimates for various parts of the project and are used to evaluate the acceptability of bids and the financial feasibility of the project
estimates
This is a drawing of the facility as it would look to an observer directly above it.
plan view
This view has elevation as its vertical axis and horizontal distance, measured perpendicular to the centerline, as its horizontal axis.
geometric cross section
This applies to curved facilities, such as highways or railways, only. It consists of a graph with roadway or railway cross- slope versus horizontal distance.
super elevation diagram
The primary consideration in the design of geometric cross sections for highways, runways, and taxiways is
drainage
The distance between the rails is what known as
standard gauge
The calculation of the distance the line needs to traverse in order to gain a certain amount of elevation, given a maximum grade, is known in railway practice as
development
Geometric design of transportation facilities must provide for the rosolution of traffic conflicts. In general, these may be classified as
I-Merging conflicts-occur when vehicles enter atraffic stream
II-Diverging conflicts-occur when vehicles leave the traffic stream
III-Weaving conflicts-occur when vehicles cross paths by first merging and then diverging
IV-Crossing conflicts- occur when they cross paths directly
I,II,III,IV
There are three basic ways of resolving crossing conflicts.
I.Time sharing solutions - involve assignment of the right-of-way to particular movements for particular times
II. Space-sharing solutions - convert crossing conflicts into weaving conflicts
III. Grade-separation solutions - eliminate the crossing conflict by placing the conflicting traffic at different elevations at their point of intersection
I,II,III
Freeway interchanges are classified primarily according to the way in which they handle left- turning traffic.
I. Diamond interchanges - employ diamond ramps, which connect to the cross road by means of an at-grade intersection.
II. Cloverleaf intersections - employ loop ramps, in which vehicles turn left by turning 270° to the right
III. Direct interchanges -
employ direct ramps, in which vehicles turn left by means of a left-tuming ramp that is grade-separated as it crosses both traffic streams.
I,II,III
It is used to provide access to adjacent property
Frontage roads
It is used to intercept traffic from local streets that do not cross the freeway
Collector-distributor roads
Wherever the existing ground is above the constructed section, the construction is said to involve
cut or excavation
Wherever the existing ground is below the constructed section, the construction is said to involve
fill or embankment
The points at which the cut or fill slopes intersect the existing ground are referred to as
catch points
The points at which the cut or fill slopes intersect the nearly horizontal roadway surface are referred to as
hinge points
A graph of cumulative volume of earthwork versus distance in stations from the beginning of the job, in which cut is considered to be positive and fill negative.
Mass diagram
The longest distance material should ever be hauled is called the
limit of economic haul
It usually consists of asphalt or Portland cement concrete
Surface courses
A series of interconnected or interlaced cracks caused by fatigue failure of the asphalt concrete surface under repeated traffic loading.
Alligator cracking
Cracks forming large interconnected polygons, usually with sharp comors or angles. Those cracks are generally caused by hardening and shrinkage of the asphalt and/or reflection cracking from underlying layers such as cement-treated base.
Block cracking
Cracks approximately at right angles to the pavement center- line. These may be caused by shrinkage or differential thermal stress of the asphalt concrete, or may be reflective cracks.
Transverse cracking
Cracks approximately parallel to the pavement centerline. These are caused by poorly constructed construction joints and shrinkage of the asphalt concrete surface; they may also be reflective cracks.
Longitudinal cracking
Progressive disintegration of the surface between the wheel paths caused by dripping of gasoline or oil from vehicles
Drip track raveling
The exuding of bitumen onto the pavement surface, causing reduction in skid resistance.
Bleeding or flushing
Elevation differences between adjacent slabs at transverse joints
Faulting
Local sagging in the pavement caused by differential settlement, consolidation, or movement of the underlying earth mass
Settlement
Localized upward buckling and shattering of the slabs at transverse joints or cracks.
Blowups
The breakdown or disintegration of slab edges at joints or cracks, usually resulting in the loss of sound concrete and the progressive widening of the joint or crack.
Joint or crack spalling
Loss of the original surface texture due to traffic action
Surface Polish
The overall track structure typically consists of
I subgrade
II. ballast
III. ties
IV. rails
V. rail fastening
all of the above
The product of a volume of material times the average distance it is hauled is referred to as
haul
They normally consist of aggregates such as gravel and crushed rock
Base courses
The characteristics of the subgrade, subbase, and base layers may be expressed in terms of a
resilient modulus or a relative bearing capacity
Abnormal surface wear, usually resulting from poor-quality surface mortar or coarse aggregate.
Surface attrition or surface abrasion
They are usually local aggregate materials. They may be consist of either unstabilized compacted aggregate or stabilized materials.
Subbases
Used to fasten rails together longitudinally,
Joint bars
Sleel bars used to maintain gage (that is, horizontal separation between the rails) at critical locations such as curves and switches.
Gage bars
Used to resist the longitudinal motion of rails relative to ties.
Rail anchors
When such motion takes place along a single linear facility such as a roadway or a railway, it can often be represented by a graph known as
Space-time diagram
It may be defined as the difference between the actual travel time on a given segment of a transportation system and some ideal travel time for that segment.
Delay
The difference between A(t) and D(t) represents aircraft that have arrived at the runway but have not begun (or completed) their takeoffs. These line of aircraft waiting to be served is called a
queue
From queuing diagram, it is possible to determine a number of interesting things:
I. The number of customers in queue at any given time, or queue length
II. The delay to each customer, assuming the order of service is the same as the order of arrival.
Ill. The summation of delay to all customers. IV. Given the density of the queue, the physical length of the queue, or the amount of space required for its storage.
I,II,III
Queueing diagrams have several important properties:
I. The slope of D(t) is the departure rate; the slope of A(t) is the arrival rate. II. The departure rate cannot exceed the service rate or capacity of the server. It may be less.
III. Cumulative departures can never exceed cumulative arrivals. D(t) can never be above A(t) in the queueing diagram.
IV. When a queue is present, the departure rate will equal the service rate. When no queue is present, the departure rate will equal the arrival rate. The queue first forms when the arrival rate first exceeds the service rate.
I,II,II and IV
So far, no explicit consideration has been given to the relationship between the order in which customers arrive demanding service and the order in which they are served. This relationship is referred to as the
queue discipline.
It is defined as the number of vehicles per unit time passing a point in space, and is usually expressed in vehicles per hour.
flow
It is the number of vehicles counted in a specified time interval.
volume
They are measured between common points on successive vehicles
headways
They are measured from the rear of one vehicle to the front of the next
time gaps
It is defined as the number of vehicles per unit distance occupying a section of roadway at a given instant in time
density
Models of traffic flow are often classified as microscopic or macroscopic.
I. Microscopic models describe the motion of individual vehicles and their interactions with one another
II. Macroscopic models describe the relationships among speed, flow, and density.
I and II
It is defined as the maximum number of vehicles, passengers, or the like, per unit time, which can be accommodated under given conditions with expectation of occurrence. a reasonable
Capacity
The red, yellow, or green light that is displayed to drivers in a given movement is called an
indication
The time required for one complete sequence of signal indications is called a
cycle
The discrete portion of a cycle during which the indications do not change is called an
interval
The portion of the cycle during which the movements with the right-of-way do not change is called a
phase
It is the timing of signals in relationship to one another so that vehicles traveling at a predetermined speed can pass through the greens of successive signals.
Signal coordination
The speed at which vehicles are presumed to travel through the coordinated signal system is known as the
speed of progression
The space-time path intersecting the green at all signals is called the
through band
The time difference between beginning and end of the through band at any point is known as the
band width
In this system, each signal displays the phase opposite that of the adjacent signals; thus the pattern, looking down the street at any instant of me, is red-green-red-green
Single alternate system
It groups three intersections and produce a pattern of red-red-red-green-green-green.
Triple alternate system
The best established form of freeway trafficcontrol is ramp metering
I. Objectives of ramp metering
II. Minimization of delay and congestion
III. Improved safety
IV. Smoother traffic flow
I II III IV
Employing minimum cycles are usually sufficient for platoon-breakup metering.
Fixed-time systems
The time spent in decelerating and accelerating the vehicle and in opening and closing the doors.
Clearance time
Route schedules, or timetables, give the times that successive bused pass points called
time points
Headways such that the vehicles are just filled at the maximum load point on the route.
Capacity headways
Arbitrarily determined maximum headways intended to represent the minimum acceptable standard for frequency of service.
Policy headways
It is considered to be the basic unit of travel behavior. It also involves movement from a single origin to a single destination, and are usually described in terms of their origins, destinations, purposed, times of occurrence, travel modes, and routes.
Trip
This means that the utility of any particular trip is partially dependent on the activity it makes possible, and the way in which that activity is valued by the individual.
Derived utility
These are intended to predict the number of travelers using various routes and, hence, the traffic on the links of a transportation network.
Trip Assignment Models