Safety Benefits
- Fewer conflict points (14 for DDI, 26 for conventional)
- Conflict points spread out throughout interchange
- Better sight distance at turns
- Virtually no driver confusion (FHWA study and new DDI observations in Springfield, MO)
- Traffic calming features when desired
- Wrong way entry to ramps extremely difficult
- Pedestrian crossings are shorter
Supporting Data
- MODOT survey shows that 97% of drivers feel safer in the new Springfield DDI compared to the previous diamond interchange
- Crash data for the new Springfield DDI show a 60% reduction in collisions in a five-month comparison of the old interchange
- Versailles, France DDI showed that within a five-year time span that was examined, there were only been 11 reported light crashes
Operational Benefits
- Unique phase combinations
- “Free” or simple left and right turns from all directions
- Increases left turn lane capacity without needing more lanes
- Only two phases needed, shorter cycle length
- Lanes with multiple assignments in all directions
- Better storage between the ramp terminals
- More functional during a power outage
- U-turns from highway are accommodated well
- Better signal network synchronization
Supporting Data
- MODOT survey shows that 95% of drivers felt that there was less congestion in the new Springfield DDI compared to the previous diamond interchange
- Daily traffic backups that sometimes had over a mile queue were completed eliminated once the construction of the new Springfield DDI was complete.
Cost Benefits
For a retrofit
- Existing bridge can usually be used
- Additional right-of-way rarely needed
- Construction time is reduced
- Maintenance of traffic is simplified during construction
For a new interchange
- Fewer lanes than other interchange forms
- Less bridge structure
- Less right-of-way than a cloverleaf form