3. CEE320
Winter2006
Conceptos
• El alineamiento en un problema en
3D representado en dos problemas
2D
– Alineamiento Horizontal (planta)
– Alineamiento Vertical (perfil)
• Progresivas
– A lo largo del alineamiento horizontal
– 12+300 = 12300 m
7. CEE320
Winter2006
Alineamiento Vertical
• Objetivo:
– Determinar cotas para asegurar
• drenaje
• aceptable nivel de seguridad
• Primer desafío
– Transición entre dos pendientes
– Curvas verticales
G1 G2
G1
G2
CV Convexa
CV Cóncava
8. CEE320
Winter2006
Fundamentos Curva Vertical
• Función parabólica
– Tasa constante de cambio de pendiente
– Implica tangentes iguales (proyectadas sobre
la horizontal)
• y es la cota de rasante, x las progresivas
desde el comienzo de la curva
cbxaxy ++= 2
10. CEE320
Winter2006
Relaciones
Choose Either:
• G1, G2 in decimal form, L in feet
• G1, G2 in percent, L in stations
G1
G2
PVI
PVT
PVC
L
L/2
δ
x
1and0:PVCAt the Gb
dx
dY
x ===
cYx == and0:PVCAt the
L
GG
a
L
GG
a
dx
Yd
2
2:Anywhere 1212
2
2
−
=⇒
−
==
11. CEE320
Winter2006
Otras Propiedades
• El Valor-K defines la curvatura vertical
– Es la longitud horizontal necesaria para un
cambio de pendiente de 1%. En el sistema
métrico la unidad es m/%.
A
L
K =
1./ GKxptlowhigh =⇒
21. CEE320
Winter2006
Alineamiento Horizontal
• Objetivo:
– Geometry of directional transition to ensure:
• Safety
• Comfort
• Primary challenge
– Transition between two directions
– Horizontal curves
• Fundamentals
– Circular curves
– Superelevation
Δ
22. CEE320
Winter2006
Fundamentos de Curva Horizontal
R
T
PC PT
PI
M
E
R
Δ
Δ/2Δ/2
Δ/2
RR
D
π
π 000,18
180
100
=
=
2
tan
∆
= RT
D
RL
∆
=∆=
100
180
π
L
26. CEE320
Winter2006
Selección de e y fs
• Límites prácticos de peralte (e)
– Clima
– Constructibilidad
– Uso del suelo adyacente
• Variaciones de Factor de fricción lateral
(fs)
– Velocidad vehículo
– Textura pavimento
– Condición neumático
42. CEE320
Winter2006
Curvas Espirales
• WSDOT no usa curvas espirales
• Involucra geometría compleja
• Requiere más relevamiento
• Son algo empíricas
• Si se usan, la transición del peralte debe
realizarse en toda la espiral
PARA DISCUTIR
44. CEE320
Winter2006
Velocidades de Operación y
Directriz
Velocidad 85º Percentil vs.
Velocidad Directriz Inferida
según 138 Curvas
Horizontales de CR2C
Velocidad 85º
Percentil vs.
Velocidad Directriz Inferida
con DVD limitada por Curva
Vertical Convexa
45. CEE320
Winter2006
Referencias
• Mannering, F.L.; Kilareski, W.P. and Washburn, S.S. (2005).
Principles of Highway Engineering and Traffic Analysis, Third
Edition. Chapter 3
• American Association of State Highway and Transportation
Officials (AASHTO). (2001). A Policy on Geometric Design of
Highways and Streets, Fourth Edition. Washington, D.C.
Notas del editor
Therefore, roads will almost always be a bit longer than their stationing because of the vertical alignment
Draw in stationing on each of these curves and explain it
Typical set of road plans – one page only
G is in percent, x is in feet
G is in decimal, x is in stations
Minimum lengths are about 100 to 300 ft.
Another way to get min length is 3 x (design speed in mph)
What can you do if you need a shorter sag vertical curve than calculated? Provide fixed-source street lighting
Minimum lengths are about 100 to 300 ft.
Another way to get min length is 3 x design speed in mph
Trinity Road between Sonoma and Napa valleys
D = degree of curvature (angle subtended by a 100’ arc)
Divide both sides by Wcos(α)
Assume fse is small and can be neglected – it is the normal component of centripetal acceleration
The maximum side friction factor is the point at which the tires begin to skid
Design values of fs are chosen somewhat below this maximum value so there is a margin of safety
There is a different curve for each superelevation rate, this one is for 8%
Basically it’s figuring out L and M from the normal equations
Can also rotate about inside/outside axis
Ease driver into the curve
Think of how the steering wheel works, it’s a change from zero angle to the angle of the turn in a finite amount of time
This can result in lane wander
Often make lanes bigger in turns to accommodate for this