CE561 Assigned: 5/22/06 Mon Due: 5/24/06 Wed

CE561 Assigned: 5/22/06 Mon Due: 5/24/06 Wed

Homework #7

Vertical Alignment (Grades, Climbing Lanes, Passing Lanes, Turnouts)

Problem 1. (10 points) If a typical heavy truck enters a 5% upslope at 40 mph, how much speed reduction it will experience after 1500 feet of travel on the upslope?

Problem 2. (10 points) If a typical heavy truck is entering a 6% upslope at 20 mph, can it speed up to 30 mph from there? If not, up to about how fast can its speed increase and where from its entry does it reach a crawl speed?

Problem 3. (10 points) Suppose a highway is designed for 70 mph and has a fairly level approach to a 5% upgrade. What would be the critical length of the 5% grade?

Problem 4. (10 points) What would be the critical length of a 6% grade approached by a 1000ft length of 3% grade if the 10-mph speed reduction criterion is used?

Problem 5. (10 points) Define the turnout first. Then, state the recommended lengths for turnouts. Draw turnouts for the approach speed of 30 mph and 60 mph, with tapers of proper lengths, together with its widths and installation locations as recommended by the Greenbook.

Problem 6. (50 points) Use the handout given for Problem 7 of Homework #6.

6.a Draw a profile on an engineering paper and add a vertical alignment (a rough design is fine at this stage). Assume we have a near-level end connection to the existing road and the observation area, which gives you at minimum two VPIs. Make a couple of copies of the profile first because you need them for problem 6.c.

6.b Check how much speed reduction will trucks and RVs have on the grade you chose (Estimate from your profile) that you chose for your best route. Make a rough estimate of the length, from the first VPI to the next VPI. Note the running speed is typically slightly lower than the design speed. See Exhibit 3-14: Average Running Speeds.

6.c What would be the critical length of this slope if you use the 10-mph speed reduction? Check for the trucks and RVs. Do you need to reconsider your vertical alignment if the 10-mph speed reduction is applied? If so, redraw the profile and add

6.d Do you need a climbing lane, passing lane, or turnout? Discuss reasons why you need them or not. Whatever you choose, give possible dimensions.

6.e Where in your alignment do you place the auxiliary lane or turnout that you chose in problem 6.d? If you do not need any of these, at least place one turnout in each direction. Give their dimensions.