Problem 3



CEE 320 Midterm Examination (50 minutes)

• Please write your name on this cover.

• Please write you last name on all other exam pages

• This examination is open-book, open-note.

• There are 5 questions worth a total of 100 points.

• Each question lists the point value for that question.

• Please work quietly and respect other people’s space.

• Carefully read each question and ensure that you answer what is asked.

• If you need additional workspace, use the back of the page or the blank page included at the end of the examination.

• If you need to unstaple pages, I have a stapler to restaple them at the end of the examination.

Name (first, last): ___________________________________________

Question 1: Short Answers (5 points each for a total of 20 points)

A vehicle is able to achieve a maximum deceleration of 0.10 g’s (1 “g” is the force of gravity at sea level). If the vehicle is traveling packed snow, what is the vehicle’s braking efficiency? Show your calculations.

Based on the short reading, Reconsidering the Gas Tax: Paying for What You Get, is the author in favor of or opposed to the gas tax?

A two-lane road (12 ft wide lanes) has a 575 ft long horizontal curve with a central angle of 30° and a 10% superelevation. What is the curve’s design speed to the nearest 5 mph?

In situations where the stopping sight distance (SSD) is greater than the vertical curve length, is the listed curve length in the design tables (Table 3.2 and 3.3 in your text) more than or less than the actual required vertical curve length based on actual geometry?

Circle one: More than actual curve length

Less than actual curve length

Problem 2 (15 points)

A garbage truck has axle weights shown in the table below. Using the 4th power thumbrule, estimate how much more damage a full garbage truck does to the pavement than an empty one. Express this quantity as a multiple of the empty damage. For instance, “the full truck causes XX times more damage than the empty one”.

|Condition |Front Axle Weight |Rear Axle Weight |

|Empty (no garbage) |6,000 lb |10,050 lb |

|Full of garbage |8,250 lb |23,000 lb |

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Picture from Heil Environmental Industries, Ltd. ()

Problem 3 (20 points)

Where long, descending grades exist, runaway truck ramps are placed at appropriate locations such that vehicles that have lost braking ability (e.g., brakes overheated or mechanical failure) can steer onto them and use gravity and rolling resistance to stop their vehicle in a safe manner.

Complete the following runaway truck ramp design. The ramp, surfaced with pea gravel, must allow a semi tractor-trailer traveling at 60 mph at point A to stop completely over a distance of 600 ft without the use of brakes (no brake force is applied because the brakes are assumed to have failed completely). Guidance is as follows:

• Mass factor accounting for moments of inertia during braking = 1.04

• Assume the vertical curve at point A is small enough to ignore.

• Ignore the contribution of aerodynamic resistance to theoretical stopping distance.

• Do NOT use the practical SSD formula because it does not explicitly account for rolling resistance. Use theoretical stopping distance.

• Note that pea gravel has a different equation for rolling resistance than pavement.

Determine the required grade of the runaway truck ramp to allow the truck to stop exactly at point B, 600 ft from point A.

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Problem 4 (15 points)

Design a NASCAR race track with a race car design speed of 120 mph through the turns. The limiting side friction factor for NASCAR design on this race track is fs = 0.25. You MUST account for the effects of the downward component of centripetal acceleration (the fs×tanα portion of the equation that is typically assumed to be zero). Assume the position of the limiting vehicle is at the center of the track width (Rv = R). The 1500 ft measurement is from center of track width to center of track width. Your design should include reported values for:

• Curve radius

• Curve length

• Superelevation in percent (need to convert the bank angle to superelevation)

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Bonus: what does “NASCAR” stand for?

Problem 5 (30 points)

Design a vertical curve with the given PVI to go through a future intersection location at the point at which the vertical curve is flat.

Report the station and elevation of the vertical curve’s PVC and PVT.

Report the vertical curve’s design speed to the nearest 5 miles per hour.

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Blank Page for Additional Work Space

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Plan View of Track Centerline

PVC

Station = ?

Elevation = ?

•

PVT

Station = ?

Elevation = ?

Future Intersection

Station = 100+00

Flat grade here (G = 0)

PVI

Station = 99+00

Elevation = 228 ft

G2 = 1.0%

G1 = -2.6%

Straight sections are parallel to one another

Direction

of travel

Truck ramp characteristics

Surface: pea gravel

Grade: ???

Length: 600 ft

Rolling Resistance Equation for Pea Gravel

B

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A

Runaway Truck Ramp

600 ft

Main Road

Design this curve

1500 ft

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