Midterm 2 Flashcards
series of 2 or more circular curves; any 2 successive curves having a common tangent
compound curves
3 things that “define”a compound curve?
- ) Simple Curve
- ) Curvature in the same direction
- ) Common Tangent
where are compound curves used?
at grade intersections, highway sections in difficult topography, and ramps of interchanges, to avoid obstacles
ratio of compound curves for highways
1.5:1
two simple curves with equal radii turning in opposite directions with a common tangent
reverse curves
What is the purpose of reverse curves?
to change the alignment of the highway, to redirect through lanes at channelized intersections and high speed median crossovers
What is one downfall of reverse curves?
Causes sudden change in alignment which makes it hard to stay in lane
Why is vertical alignment important
to determine the elevation to ensure proper drainage, and an acceptable level of safety and comfort
What is the primary challenge of vertical curves?
Transitioning from one grade to another
two types of vertical curves
crest and sag
True or false: vertical curves have equal tangents making it symmetrical about the PVI
true
What type of shape do vertical curves most mimic, circular or parabolic?
Parabolic
how are grades selected?
based on the type of urban or rural, type of street, and design speed
location at which the curve is level/where the slope is zero
turning points
why are turning points important?
Water can collect
number of horizontal feet needed for a 1% change in the slope; also known as vertical curvature
k factor
what can the k factor be used for?
Finding high/lowpoints
What is the goal of SSD considerations?
to find an appropriate length (L) for the curve that can accommodate the correct SSD
Advantages of transition curve advantages
appearance of the highway is enhanced, reduces break in alignment, suitable zone for super elevation runoff
curves placed between tangent and circular sections of roadway; beginning with an infinite radius to match the tangent ending with the same radius as the curveS
transition curves
Curve where the radius is infinite at the tangent end and radius of circular curve at the other end
Spiral Curve
Where can spiral curves be located
approaching a curve, leaving a curve, connect two circular curves of differential radii
does the central angle change when reducing to a spiral curve?
no but the curve angle gets reduced by -2delta
General types of roadways
divided and undivided
types of undivded roadways
- ) 2-lane undivided
- ) 3-lane undivided
- ) multi-lane undivided
types of divided roadways
multi-lane divided
number of lanes eq
DDHV/SFL
what does lane width depend on
classification, volume, design speed
how do you widen the pavement for simple curves?
widen the inside edge of traveled way only
how to widen pavement for spiral curves
widen inside edge of traveled way; mark centerline midway between edges of pavement
what is the cross slope used for?
necessary for proper drainage; prevents ponding on surface, determined on construction technologies, materials and equipment
provided along the road edge to serve as an emergency lane for vehicles
shoudlers
normal width of shoulder
10’
portion of highway separating opposing directions of travel; dimenson between the edges of traveled way; includes shoulder width
median
three types of medians
raised, depressed, flush
widths of medians
4-84 feet
where are median openings and what do they do?
3 mile intervals; provide u turn capabilities
how much feet permits recovery of vehicles
30 feet
What is a clear zone based on
volumes, speed, roadside slopes
How does a curve clear zone vary?
you must provide 50% more Clear zone
what do you place on shoulder if clearzone obstructions are not removable?
guardrails
the boundaries between the pavement and shoulders/footpath
curbs
designates traveled way cross section used on curves
normal crown
between normal crown and full superelevated
reverse adverse crown
super elevation transition =
tangent runout to superelevation run off
gradual change from crown normal to a point where the adverse cross slope is removed
tangent runout
gradual change from end of tangent runout to a cross section that is fully superelevated
superelevation runoff
