Why not a cloverleaf at Rt. 59 and I-88?

On July 14, the Illinois Department of Transportation presented its plan for the upcoming upgrade of Route 59. A major component of the project is the redesign of the Rt. 59 & I-88 interchange to a new type still unused in Illinois called a "diverging diamond."

The engineers that I talked to were very nice but could not explain why IDOT keeps trying to improve diamond-style interchanges that generate acute traffic congestion rather than upgrading to a free flowing cloverleaf with no traffic signals and minimal congestion. The only explanation I could get was "cloverleafs take more right-of-way."

Cost really isn't an issue because the cost of designing, constructing, maintaining and repairing traffic signals over a 20 - 30 year life span probably exceeds the original cost of building a cloverleaf, assuming the right-of-way is available.

The new "diverging diamond" will reroute motorists on Route 59 to the other side of the roadway so left turns onto the tollway ramps do not cross in front of opposing traffic. While this design reduces points of vehicle conflict and reduces collisions, it has a cost in traffic flow. For example; every time northbound Route 59 is rerouted to the southbound side of the tollway bridge to get closer to the westbound on- ramp, all southbound Route 59 traffic must be halted or diverted to allow that to happen. By allowing both directions to shift at the same time, the amount of time it takes to cross the divergence is available for a cycle. The end result is a safer interchange with simpler traffic lights, but a new alternating flow pattern that intermittently stops all Route 59 through traffic.

The new design is definitely superior to the existing system of multiple turn arrows and light cycles competing for time in the overall traffic cycle but substantially inferior to a free-flowing cloverleaf that requires no signals.

Charles Murphy

Glen Ellyn