Interstate 435and Front Street
Interchange Improvements
Project Location
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.
Project Scope
Initial Concepts We Reviewed
Single Point (SPUI)
Half-Cloverleaf
Roundabout
Tight Urban Diamond (TUDI)
Single Point (SPUI)
Problems with a Single Point design
Required extensive reconstruction of I-435.
Costs for additional right-of-way and construction were very high, about$31 million.*
We had concerns about how long it would take trucks to clear such a large intersection.
*Based on 2002 estimates.
Half-Cloverleaf
Problems with a Half- Cloverleaf design
Required large amounts of new R/W.
Costs for additional right-of-way and construction were very high, about$37 million.*
We had concerns about the trucks being able to accelerate from the loop ramps onto the freeway.
*Based on 2002 estimates.
Roundabout
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.
Tight Urban Diamond (TUDI)
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, about$28 million.*
*Based on 2002 estimates.
Initial Design
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.
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.
Conflict Point Diagram - TUDI
Problems with the initial designTriple 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.
A Practical Design Solution
A Diverging Diamond Interchange or DDI
Diverging Diamond Design
Link to DDI overhead videoLink to one of the drive thru videos
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.
AdvantagesThis 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 don’t have to look through bridge columns to see on-coming traffic.
AdvantagesIt 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.
Conflict Point Diagram - DDI
AdvantagesThe 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.
Estimated Costs* Initial DDI Construction
MoDOT $ 6,763,000 $4,097,000Kansas City $ 103,000 $ 71,000
Right of WayMoDOT $ 1,823,000 $ 625,000Kansas 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.
Disadvantages of a DDIDriver 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.
DDI One construction season
Length of Construction
Two construction seasons
TUDI
ConclusionThe 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.