CE 453 Lab #13Page 1 of 5

INTERSECTION DESIGN

PROBLEM:

You are to design an urban, at-grade intersection for an intersection in Ames, using different design criteria for each approach and quadrant of the intersection to demonstrate knowledge of various design types. This assignment is due November 30th.

Helpful links:

The class website, at lecture 32, has an Excel spreadsheet for (3-center) compound curve design. You may find it helpful to use it in the design of one of your curb returns.

You can refer to a typical set of plans in room 220 to determine what should be included on the intersection plan sheet.

COMPLETION STEPS:

  1. Develop the design traffic and projected turning movement counts for the project. Use a ½% annual traffic growth rate, a thirty-year design life, and assume that the peak hourly traffic is 10% of the ADT. The Excel file Lab 13 Base Traffic.xls contains the base traffic by direction.
  2. Open Microstation and create a new drawing. Bring in the drawing Lab 13 Base.dgn as a reference file; it is on the lab instructions site. This intersection is at Elwood and Airport Road on the south side of Ames. The dimensions on the reference drawing are for your information and use, since they are on a separate level you can turn that level off to hide the dimensions in your final drawing.
  3. Your job will be to design improvements to the intersection. These improvements are to provide four lanes with left-turn lanes for the south and west approaches. You will also redesign the two existing left-turn bays as given below. You are to modify the existing right turn curbs as given below.
  4. Assume the design vehicle is a B-40bus (the B-40 has the same requirements as the SU). You will also test your design with a WB-50 truck.

All curves must be designed such that the design vehicle does not encroach on other lanes or go off the pavement when going around a curve. The WB-50 truck must be able to turn without encroaching on the curb or the median but it can use both lanes.

For right turn curbs, use 4 methods of curve design (one for each quadrant):

SW – Simple circular – if no guidance is given in the Green Book, choose a curve with a radius R that will accommodate the turning template

SE – Compound symmetric

NE – Compound asymmetric

NW – Simple circular with tapers

For left turn bay transitions, use 4 methods of attainment (one for each quadrant):

S – Straight-line taper

E – Partial tangent taper

N – Symmetrical reverse curve

W – Asymmetrical reverse curve

Design the left turn bay, using the provided in your packets for each of the longitudinal dimensions. Calculate or otherwise determine the length of the storage space and the length of curves and tapers required to provide a 12-foot lane with median widths the same as existing (4-foot minimum N-S and 6-foot minimum E-W).

4. Show the critical points and lengths associated with the development of each turning bay at the intersection on a detailed plan sheet at an appropriate scale (1” = 40’).

  • Graphic scale, directional arrow, title block, and your team name
  • Pavement widths
  • Lane markings (use Microstation line styles)
  • The trace of the B-40 should be shown on the diagram for each of the turns. Assume all through lanes are 12feet wide as a minimum; assume all lanes that are constrained by a median are16feetwide.

Procedure

Use the Microstation and Geopak tools to do your graphic work. In your design drawing, go to the Geopak project manager work flow and click on Horizontal Alignment. Click on Tools>Curve Combinations to get the following tool bar

From left to right these tools are as follows:

  • Place Turning Path – gives you a simplistic turn template for the vehicle you select.
  • Place Compound Curve – places a compound curve for radii you enter.
  • Place Three Centered Curve – generates a three-centered curve using either radii and offsets you select or the design vehicle you choose.
  • Place Taper Curve – generates a taper-curve-taper combination using values you enter.
  • Place Reverse Curve – generates a reverse curve combination using values you enter.

Use values from the Green Book (see below) for the appropriate design vehicle. Generally you should select the “both” option under the truncate choice.

Use each of the methods as directed above. When you have placed a curve, use the Place Turning Path tool to place the path of a B-40 vehicle as a check on your design. Be sure your turning vehicle path does not encroach on the curb or islands. Use the AutoTurn software to place a B-40 or SU vehicle. The procedure is as follows:

  • Go to Utilities>MDL Applications and click on Browse. You should get atv8 as your choice, select it. You should have the following toolbar:
  • Click on the first button on the left (looks something like a wrench) and make sure the drawing master units are set to feet.
  • Using the Microstation drawing tools, place a continuous line for the travel path of the vehicle. Be sure to connect the lines you draw. If you place too small a radius you will get an error message. You will have to delete the circular portion of the line and place a larger radius.
  • In Auto Turn click on “Vehicles” (third from the left) and select the B-40 bus or the SU. Now click on “Select Active Simulation” (fourth from the left), select the completed path, and click again in the direction of travel. Finally click on “Place Simulation.” (the button below) The vehicle should be placed.
  • Check for encroachments and fix any you find. Do a final check with the WB-50 vehicle.
  • Repeat until there are no encroachments.

After you have used these tools and placed your curves you will need to clean up your drawing by replacing the various crosses that denote the key points along those curves. Use the Microstation circle tool to place 6.0-foot diameter circles at these points. Number these points and provide stationing and “distance” (offset) as in the example. Tabulate the stationing of these points as well as the circular curve data. Also be sure to round off median noses and the corners of islands, if any.

You should be aware that we have some limitations on our Auto Turn license. It allows for five (5) simultaneous users, all on campus. You will not be able to do this part of the lab on your personal computers. If you do the rest of the lab on your personal computer you will need to do this portion in one of the computer labs in Town Engineering.

GRADING CONSIDERATIONS AND EXPECTED RESULTS:

Use the design policies in Chapter 9 of the Green Book and the lecture discussion for design.

Some helpful reference tables and charts:

Exhibit 9-95 (p. 722) – Taper design for auxiliary lanes

Exhibit 9-41 (p. 640) – Minimum turning roadway designs

Exhibit 9-42 (p. 642) – Minimum designs for turning roadways

Exhibit 9-24 (p. 604) – Minimum edge-of-traveled-way designs

Exhibits 9-19 and 9-20 (pp. 588-595) – Edge of traveled way design specs for curves

GRADING CRITERIA
  1. Brief memorandum presenting the intersection design justification andcalculations or documented method (e.g. copy of nomograph) and assumptions (total of 30%).
  1. Design traffic determination and map of turning movements (a sketch-type plan showing where the peak-hour traffic goes)15%
  1. State assumptions and document your recommendations. Design a turn bay for each approach. Show all calculations or references used in the design process for each part of the turn lanes. (Includes traffic volume assessment), 15%
  1. Intersection design, 1” = 40’ (total of 55%)

Intersection plan must include all items typically included in an Iowa DOT set of plans. See example plan provided, sheet L-01, attached. All sheets to be no larger than 11” X 17”. If your plan will not fit on one sheet at this scale you will need to prepare more than one sheet, each showing a part of the intersection.

  1. Stationing and offset of important points, 6%
  1. Curves, numbered starting in NW quadrant, proceeding clockwise, with data (“Circular Curve System”) 15% (ignore the curve data found to the right of curve 11; also note that north is not up on the example plan, but you should make north the up direction on your plans)
  1. Lanes, medians, total roadway, and right-of-way (dimensioned), 10%
  1. Pavement markings (approximate layout location and be sure to use the appropriate line styles), 7%
  1. Full width turn lanes,3%
  1. A trace of the turn template lines (design vehicle) for right and left turns on each approach (these indicate the ability of your design to accommodate the design vehicle),10%
  1. Identifying information (lower margin), title block, scale, north arrow, etc., 4%
  1. Overall plan at a scale to show the entire project including the ends of the turn bays on a single 11” X 17” sheet -- 15%
  1. Grammar/style -- up to 30% penalty for poor grammar/style/presentation.