Interstate 435 and Front Street Interchange Improvements

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Interstate 435and Front Street Interchange
Improvements

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Project Location
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Purpose and Need for this project

• To provide safety improvements at the northbound
  and southbound exits from I-435, within the
  interchange on Front Street and the entrance ramp
  onto southbound I-435.

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(No Transcript)
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Initial Concepts We Reviewed
Single Point (SPUI) Half-Cloverleaf
Roundabout Tight Urban Diamond (TUDI)
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Single Point (SPUI)
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Problems with a Single Point design

• Required extensive reconstruction of I-435.
• Costs for additional right-of-way and
  construction were very high, about31 million.
• We had concerns about how long it would take
  trucks to clear such a large intersection.
• Based on 2002 estimates.

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Half-Cloverleaf
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Problems with a Half- Cloverleaf design

• Required large amounts of new R/W.
• Costs for additional right-of-way and
  construction were very high, about37 million.
• We had concerns about the trucks being able to
  accelerate from the loop ramps onto the freeway.
• Based on 2002 estimates.

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• Roundabout

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Problems with a Roundabout design

• Did not perform as well as other alternatives.
• We had concerns about the operation of the trucks
  in the roundabout (two trucks likely would not
  enter a roundabout at the same time, reducing
  capacity).
• Costs for additional right-of-way and
  construction, about 10 million.
• Based on 2002 estimates.

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Tight Urban Diamond (TUDI)
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Problems with a Tight Urban Diamond design

• Required considerable reconstruction of I-435.
• Did not work as well as the SPUI or
  half-cloverleaf.
• Costs for additional right-of-way and
  construction were high, about28 million.
• Based on 2002 estimates.

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Initial Design
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Initial Design

• The existing interchange is very similar to a
  TUDI, with I-435 over Front Street.
• The initial preliminary design included
• Adding lanes to the off ramps with double and
  triple left turn lanes.
• Adding lanes to Front Street between Universal
  and Corrington with traffic lanes behind the
  bridge piers.

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Problems with the initial design

• The life of the capacity improvements were
  limited. This design would probably fail within
  10 to 15 years.
• The Levels of Service were D, E and F.
• Costs for additional right-of-way and
  construction were still somewhat high, about 11
  to 12 million.
• This design has 45 conflict points within the
  entire interchange.
• Based on 2005 estimates.

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Conflict Point Diagram - TUDI
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Problems with the initial design

• Triple left turn lanes were needed for the
  northbound to westbound movement. This is not
  desirable with 11 trucks during peak hour. (Off
  peak has about 30 trucks.)
• Seven lanes were needed under the bridges,
  requiring construction of lanes and retaining
  walls behind the bridge piers in existing sand
  fills. This would be difficult to build.
• The trucks required large turning radii to
  achieve capacity improvement. This limited
  vehicle storage between the signals.

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A Practical Design Solution

• A Diverging Diamond Interchange or DDI

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Diverging Diamond Design
Link to DDI overhead video Link to one of the
drive thru videos
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Advantages of using a DDI at this Location

• The DDI doubles the capacity of the left turn
  lanes and eliminates the need for the triple left
  turn. The double left turn should be safer than a
  triple with high truck volumes.
• Levels of Service are A, B and C.
• This design reduces the number of lanes required
  under the bridge to four, eliminating the need to
  build retaining walls.

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Advantages

• This also reduces the number of lanes needed on
  Front Street beyond the interchange.
• This DDI design has more storage room between the
  ramp signals.
• (550 vs 350)
• This design will also provide better sight
  distance. Drivers on the ramps dont have to
  look through bridge columns to see on-coming
  traffic.

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Advantages

• It incorporates roadway features which calm
  traffic and reduce speeds while maintaining
  capacity. This should result in fewer and less
  severe crashes.
• Although wrong way entry into opposing lanes is
  possible, wrong way entry onto the ramps and the
  interstate will be almost eliminated.
• The DDI has 21 conflict points compared to 45
  with the initial design.

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Conflict Point Diagram - DDI
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Advantages

• The smaller ramp intersections mean vehicles will
  have shorter clearance times resulting in less
  exposure and safer conditions.
• The DDI design has reduced the cost of the
  project.

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Estimated Costs Initial DDI

• Construction
• MoDOT 6,763,000 4,097,000
• Kansas City 103,000 71,000
• Right of Way
• MoDOT 1,823,000 625,000
• Kansas City 2,045,000 667,000
• Utility Relocations
• MoDOT 600,000 312,000
• Total Costs 11,334,000 5,772,000
• Based on 2005 estimates.

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Disadvantages of a DDI

• Driver expectations.
• We need more extensive public involvement.
• Pedestrians have to cross free-flowing ramps (or
  the crossings need to be signalized as at this
  location).
• There is very limited accident history available.
• We need additional signing, lighting and pavement
  markings.

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DDI
Length of Construction
TUDI
Two construction seasons

• One construction season

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Conclusion

• The DDI will improve safety and capacity of the
  existing interchange, at less cost and with a
  shorter construction schedule.
• It will also provide valuable information on
  function and safety that will allow MoDOT and
  FHWA to determine if use of the DDI design at
  other locations is feasible.