A  Diverging  Diamond  Interchange  (DDI)  is:    a  type  of  interchange  designed  to  increase  capacity,  decrease  congestion,  and  minimize  new  construction  cost.    

A  DDI  is  different  from  traditional  intersections  in  that  they  allow  for  free  left  turn  movements,  meaning  that  left  turning  vehicles  will  not  cross  in  front  of  opposing  traffic.    By  eliminating  this  movement  green  time  can  be  increased  resulting  in  improved  intersection  capacity  and  safety.    

 

 Key  Points  1. Improved  Safety:    

o Lower  Speeds  o Low  Conflict  Points  o Increased  acceleration  distance  on  I-­‐75  for  WB  University  to  SB  I-­‐75    

2. Improved  Traffic  Flow:    o 2-­‐phase  signals  at  the  crossing  intersections  requires  shorter  cycle  lengths    o Reduced  delays  o Increased  acceleration  distance  on  I-­‐75  for  WB  University  to  SB  I-­‐75  

o Improved  operations  at  the  University  Dr  /  High  Meadow  3. Chrysler  Drive  Access:  Proposed  project  will  provide  direct  access  from  Chrysler  Drive  to  NB  I-­‐75  without  

stopping  at  University  Drive  signal.    

4. Driver  Adaptability:  The  DDI  will  have  signs,  markings,  and  lighting  to  direct  traffic.  Studies  in  Missouri  have  confirmed  that  drivers  adapt  quickly.  

 5. Pedestrian  /  Bicycle  Facilities:  10’  wide  pathway  connecting  the  east  and  west  sides  of  the  interchange.  

 6. Decreased  Construction  Costs  &  Right-­‐of-­‐Way  Impacts:    In  2004  a  traditional  loop  ramp  interchange  

project  was  studied.  The  proposed  DDI  project  will  cost  nearly  half  as  much  as  a  traditional  loop  ramp  configuration  and  requires  permanent  ROW  from  1  parcel.      

7. Construction  is  scheduled  to  start  spring  of  2015    Results  of  2011  Missouri  DOT  Study  of  I-­‐44  and  Rte  13  DDI  (Constructed  in  2009)    

   

Traffic  operation  conclusion  included  the  following:  •  Left  turn  movements  within  the  DDI  experienced  a  noticeable  decrease  in  traffic  delay  and  traffic  queuing;    •  The  DDI,  in  the  future,  will  handle  increased  traffic  volumes  when  compared  to  a  

diamond  interchange.  The  2035  traffic  model  demonstrated  this  fact.  It  was  also  observed  on  several  occasions  during  peak  travel  periods  or  when  an  over-­‐dimension  load  negotiated  the  DDI.  The  recovery  from  traffic  back-­‐ups  created  by  these  conditions  were  normally  eliminated  within  one  to  two  signal  cycle  lengths;    •  Over-­‐dimension  loads    (over-­‐sized  trucks)  up  to  18  foot  wide  and  200  foot  long  have  successful  moved  through  the  DDI    •  The  overall  the  traffic  flow  through  DDI  is  better    Safety  conclusion  included  the  following:  •  Total  crashes  were  down  by  46%  in  the  first  year  of  operation;  •  Left  turn  type  crashes  were  eliminated  and  left  turn  right  angle  type  crashes  were  down  72%  because  of  how  left  turns  are  handled  within  the  DDI  (free  flow  movements  or  yield  control);  •  Rear-­‐end  type  crashes  were  down  slightly  that  might  also  be  the  results  of  how  left  turns  are  handled  not  under  traffic  signal  control  •  DDI’s  post-­‐construction  crash  types  are  similar  to  any  other  signalized  intersection  and  no  definite  crash  pattern  was  noticed  in  the  review  that  could  lead  to  stating  that  within  a  DDI  a  certain  type  of  crash  increased;    Public  Perception  conclusions  included  the  following:  •  A  very  high  percentage  (80%  plus)  expressed  that  traffic  flow  had  improved  and  traffic  delay  had  decreased;  •  A  very  high  percentage  (87%)  expressed  that  crash  were  more  likely  to  occur  within  a  standard  diamond  when  compared  to  a  DDI;  •  A  very  high  percentage  (around  80%)  expressed  that  larger  vehicles  and  pedestrian/bike  movements  through  the  DDI  were  better  or  similar  to  a  standard  diamond  interchange;  •  A  very  high  percentage  (91%)  expressed  good  understanding  on  how  the  interchange  operated  with  the  current  design  of  islands,  signing,  signals  and  pavement  markings.