CEE 121 Quiz 2

What two main factors govern the design of roadways

1. Human capabilities

2. vehicle capabilities

Two opposing forces that determine straight-line performance of road vehicles

1. Tractive Effort

2. Resistance

Used to determine maximum engine power a vehicle can use to overcome resistances

Tractive Effort

3 major sources of vehicle resistance

1. Aerodynamic

2. Rolling

3. Grade/Gravitational

Sources of aerodynamic resistance

1. Turbulent Flow (air around vehicle)

2. Friction of air passing over vehicle

3. Air flowing through vehicle components

One horsepower is equal to how many ft-lb/sec

550 ft-lb/sec

Accounts for 90% of vehicle roling resistance

Tire deformation

2 components make up stopping distance

1. Stopping Sight Distance

2. Length of yellow Interval

For design purposes, coefficient of friction used in calculating stopping sight distance assumes the vehicle is:

sliding on wet pavement

How many times greater is the design braking coefficient of friciton for dry pavement compared to wet pavement

2 times

What is perception-reaction time used in designing a yellow change interval at signalized intersection

1 sec

As vehicle speed increases does the coefficient of rolling resistance for road vehicles operating on paved surfaces increase proportionally?

No

Is braking force assumed to be the product of the sliding coefficient of friction on wet pavement and the perpendicular to road surface component of weight?

True

A dilemma zone at a traffic signal

approach is an upstream section of

roadway where the driver is

too far away from the stop-line to

safely continue and clear the

intersection at constant speed at the

end of a green phase, and

is also…?

the space where a vehicle is too close to the stop-line to safely stop

What (value) is the

“perception-reaction time”

used in designing a yellow

change interval at a

signalized intersection?

1 sec

In which orientation of the highway

are horizontal curves viewed?

Plan view (top down aerial)

What are four types of horizontal

curves?

1. Simple circular

2. compound curve

3. reverse curves

4. spiral curves

On what side of the centerline are

the centers of the two or more

consecutive horizontal curves of a

compound curve?

Same side

In what direction do the two

consecutive horizontal curves of a

reverse horizontal curve turn?

opposite directions

What is the purpose of banking (or

superelevation) of horizontal

curves?

Causes resultant force to act more normally to road plane and reduces F_RC

Does the minimum coefficient of side

friction (fs) need to be less than,

equal to, or greater than the

maximum superelevation (emax) for

year-round use, including under

adverse weather conditions?

Greater than

With respect to the centerline of

which lane is the traveled-path

radius RV calculated from centrifugal

force FC considerations for safe

vehicle operation on a 2-lane

highway horizontal curve?

Centerline of inside lane

What is the Caltrans maximum

allowed superelevation rate, emax,

on 2-lane highways?

12%

For a given design speed Vd, as the

superelevation rate e decreases,

what happens to the minimum

horizontal curve traveled-path

radius RV required by Caltrans?

R_V must increase

How is the length of a curve

measured when designing horizontal

curves? [around what and along

what]

Along the curve from point of curvature to tangent point

What does the deflection angle of

the PI (Δ) of a simple horizontal

curve give us? [what is it also

known as]

Total angular change in direction between back and forward tangent in horizontal curve