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Signal Coordination Example II

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					SIGNAL COORDINATION
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Signal Coordination – Example II
Signal Coordination Example II
   Find the offset for a link 1,500 ft, Given:
     platoon  speed = 40 fps
     discharge headway = 2 sec/veh

     start-up lost time = 3 seconds

     When
      a.   No standing queue at downstream
      b.   Standing queue of 8 vehicles per lane
(a) Without Queue
   Offset = tideal = L/S
     L: distance btw signalized intersections
     S: average vehicle speed (fps)

   Offset = 1500(ft) / 40 (fps) = 37.5 seconds
(b) With Initial Queue
   Offset = L/S – (Q×h +tL)
     Q:  # of vehicle of queued vehicle = 8
     h: discharge headway = 2 sec/veh
     tL: start-Up Lost Time = 3 sec.

   Offset = (1500/40) – (8×2+3) = 18.5
More Thoughts
   When there is queue at downstream
     Offset< OffsetIdeal
     Need to turn on the green early enough
      →   Queue can disappear
Signal Coordination – Example III
RP&M 26-7
   You have two intersections 3,000 feet apart and
    have achieved some success with a 50-50 split, 60-
    second cycle length, and simultaneous system.
    a)   Draw a time-space diagram and analyze the reason
         for your success
    b)   A developer who owns the property fronting the first
         2,000 feet of the subject distance plans a major
         employment center. She plans a major driveway and
         asks your advice on its location. What is your
         recommendation, and why?
      Solution (a)
   Progression Speed = 3000 /
    60 = 50 fps = 34.0 mph
   The progression speed is                 distance
    reasonable for arterial
    speeds
   Bandwidth, BW = 30 sec         3000 ft
   Bandwidth Efficiency EffBW =
    (BW/C) × 100% = 50%



                                                                   time
                                                   30 s
                                                    Cycle Length
      Solution (b)
   Assuming progression speed
    of 34 mph is representative                                     Red time for driveway
    of average speed, the ideal               distance
    location would be at the mid-
    point, or 1,500 ft from the
    first intersection
   This allows the maximum
                                    3000 ft

    green for the major driveway
    without affecting the
    bandwidths of the arterial
    progression
                                                                                                time
          Red time for arterial
                                                    30 s
          corresponds to green
          time for major                             Cycle Length         Feasible greens for
          driveway                                                             driveway

				
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