cee320 midterm exam 10 true/false (20% of points) 4 short answer (20% of points) 3 calculations (60%...
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CEE320 Midterm Exam
• 10 True/false (20% of points)
• 4 Short answer (20% of points)
• 3 Calculations (60% of points)– Homework – In class examples
Course material covered
• Introduction
• Vehicle dynamics (chapter 2)
• Geometric design (chapter 3)
• Pavement design (chapter 4 except 4.3, 4.5, including 4th power thumbrule)
Suggestions for Preparation
• Review each lecture and identify the main points and formulas. Write these on summary notes.
• For each lecture, write an question. Do this in a group, and share questions.
• Solve these questions from scratch, do not just review solutions.
• Review homework and in class examples. Do the problem yourself.
• Make a list of the tables in the text, their title, and the page number. Include a note of what it is used for.
Transportation Engineering
• The science of safe and efficient movement of people and goods
Road Use Growth
From the Bureau of Transportation Statistics, National Transportation Statistics 2003
Sum forces on the vehicle
grla RRRmaF
Aerodynamic Resistance Ra
Composed of:1. Turbulent air flow around vehicle body (85%)
2. Friction of air over vehicle body (12%)
3. Vehicle component resistance, from radiators and air vents (3%)
2
2VACR fDa
from National Research Council Canada
Power required to overcome Ra
• Power– work/time – force*distance/time
– Ra*V
3
2VACP fDRa
sec5501
lbfthp
Rolling Resistance Rrl
Composed primarily of
1. Resistance from tire deformation (90%)
2. Tire penetration and surface compression ( 4%)
3. Tire slippage and air circulation around wheel ( 6%)
4. Wide range of factors affect total rolling resistance
5. Simplifying approximation:
WfR rlrl
147101.0
Vfrl
Grade Resistance Rg
Composed of – Gravitational force acting on the vehicle– The component parallel to the roadway
gg WR sin
gg tansin
gg WR tanGg tan
WGRg
For small angles,
θg W
θg
Rg
G=grade, vertical rise per horizontal distance (generally specified as %)
Engine-Generated Tractive Effort
r
MF dee
0
Fe = Engine generated tractive effort reaching wheels (lb)
Me = Engine torque (ft-lb)
ε0 = Gear reduction ratio
ηd = Driveline efficiency
r = Wheel radius (ft)
Front Wheel Drive
LhLhfl
WF
rlr
1
max
Braking Force
• Ratio
• Efficiency
rear
front
fhl
fhlBFR
rlf
rlrrf
max
maxgb
We develop this to calculate braking distance – necessary for roadway design
Braking Distance
• Theoretical
• Practical
Gga
g
VVd
2
22
21
grlb
b
fg
VVS
sin2
22
21
Stopping Sight Distance (SSD)
• Worst-case conditions– Poor driver skills– Low braking efficiency– Wet pavement
• Perception-reaction time = 2.5 seconds
• Equation
rtV
Gga
g
VSSD 1
21
2
Stationing – Linear Reference System
Horizontal Alignment
Vertical Alignment
0+00 1+00 2+00 3+00
100 feet
>100 feet
Vertical Curve Fundamentals
G1
G2
PVI
PVT
PVC
L=curve length on horizontal
L/2
δ
cbxaxy 2
x
Choose Either:• G1, G2 in decimal form, L in feet• G1, G2 in percent, L in stations
Relationships
G1
G2
PVI
PVT
PVC
L
L/2
δ
x
1 and 0 :PVC At the Gbdx
dYx
cYx and 0 :PVC At the
L
GGa
L
GGa
dx
Yd
22 :Anywhere 1212
2
2
Other Properties
• K-Value (defines vertical curvature)– The number of horizontal feet needed for a
1% change in slope
A
LK
• A as a percentage• L in feet
Crest Vertical Curves
221
2
200 HH
SAL
A
HHSL
2
212002
For S < L For S > L
Sag Vertical Curves
G1 G2
PVI
PVTPVC
h2=0h1=H
L
Light Beam Distance (S)
tan200
2
SH
SAL
A
SSDHSL
tan2002
For S < L For S > L
headlight beam (diverging from LOS by β degrees)
Underpass Sight Distance
Underpass Sight Distance
• On sag curves: obstacle obstructs view
• Curve must be long enough to provide adequate sight distance (S=SSD)
2800 21
2
HHH
SAL
c
m
S<L
A
HHH
SLc
m
2800
2
21
S>L
Horizontal Curve Fundamentals
RD
000,18
1
2cos
1RE
R
T
PC PT
PI
M
E
R
Δ
Δ/2Δ/2
Δ/2L
2tan
RT
DRL
100
180
2
cos1RM
Stopping Sight Distance
Rv
Δs
Obstruction
Ms v
s R
SSD
180
SSD (not L)
vvs R
SSDRM
90
cos1
v
svv
R
MRRSSD 1cos
90
DRSSD s
sv
100
180
Superelevation
• Minimum radius that provides for safe vehicle operation
• Given vehicle speed, coefficient of side friction, gravity, and superelevation
• Rv because it is to the vehicle’s path (as opposed to edge of roadway)
100
2
efg
VR
s
v