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|CE361 Introduction to Tp. Engineering |Posted Wed. 27 October 2010 |

|HW 8 Solutions, μ= 71.3, σ= 20.3 |Due Fri. 5 November 2010 |

DESIGN AND CONTROL OF INTERSECTIONS

Dear Consultant:

To continue your firm’s qualification process, please demonstrate the ability of your personnel to work in teams of 3-6 people. (You may need at least four persons for Problem 4.) Work by individuals will be accepted, but a 20% penalty will be assessed.

1. (10 points) Traffic Control Devices. A concerned citizen has sent an email to the City Engineer with the following information:

“… See the attached photo [shown below]. Expect a head on collision here on Mystic Street [where the car in the photo is driving], if someone believes this is a center island and keeps to the right of this sign and ends up just keeping far enough to the right to be facing oncoming traffic. The Keep Right sign [pic] belongs on a center island or median, not here. The appropriate sign would be the Chevron Alignment Sign [pic] or the Large Arrow Sign [pic].”

|[pic] |

Because you are his most trusted staff member, the City Engineer comes to you for advice on how to respond to the citizen. He gives you time to browse through the 2009 MUTCD (online at ) before he responds to the citizen. Advise the City Engineer on how TCDs should be used at this site to maximize safety. Explain your advice, so that the City Engineer can respond effectively to the citizen. Note: The street on the left of the photo is Ridge Street, which is one-way toward you.

Avoid clutter and avoid ambiguity. I agree that the Keep Right sign is confusing and potentially dangerous (like the Keep Right sign on the guard rail in the PPt presentation in class on 15 October 2010). To prevent traffic from entering Ridge Street (the one-way street to the left of the current Keep Right sign), the Do Not Enter sign [pic] [R5-1 in MUTCD Section 2B.37] should be used. I would remove the Keep Right sign and place one Do Not Enter sign on either side of the entrance to Ridge Street. The righthand Do Not Enter sign would be placed near the curb on Ridge Street, to the left of where the Keep Right sign now is. Chevrons are used on curves; Large Arrow Signs are used when a street ends. An object marker does not seem called for here.

2. Gap acceptance. The gaps accepted and rejected in the video of 116th and Eller Road shown at the start of class on 22 October 2010 have been recorded and summarized in an Excel file. In the file, LT = left turn, RT = right turn, DAG = duration of accepted gap, and DRG = duration of rejected gap. Ignore and delete all zero entries in the DAG and DRG columns.

A. (15 points) Use the “percent” method demonstrated in FTE Section 8.1.1 to find the critical gap for left-turning vehicles. (Hint: When you sort the DAG and DRG times, you do not have to group them into 1-second intervals.) Copy and paste into your solution those lines in your sorted list that set up the linear interpolation of FTE (8.1).

B. (10 points) Repeat Part A, but for right-turning vehicles.

C. (5 points) Which type of turn should have the longer critical gap – LT or RT? Explain.

A. Critical gap for LT vehicles. The entries in the DAG and DRG columns are sorted in increasing order, and all zero entries are removed. As in Column 4 of FTE Table 8.1, the entries in the DAG% column are increasing. As in Column 4 of FTE Table 8.1, the entries in the DRG% column are decreasing. The plots for LT and RT appear in Figure 2A below. In Figure 2A, the plots of LT DRG% and LT DRG% versus Length of Gap intersect at approximately 3 seconds. The excerpt of the sorted table for Gaps just longer and shorter than 3 seconds are shown in Table 2A below. (The many duplicate entries for data points such as “2.6 sec., 19.00%” are not shown in the Table 2A excerpt.)

[pic]

Figure 2A. DAG% and DRG% plots for LT and RT gaps

|Table 2A | |Table 2B |

|Left Turns |Left Turns | |Right Turns |Right Turns |

|DAG |DAG% |DRG |

|25 |v(0)=approach speed mph | |

|2 |t(r) reaction time sec. | |

|-10 |a ................
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