1. http://goo.gl/maps/oGquM
This interchange is essential to the Strategic Intermodal System (SIS), one of the
thirteen (13 ) along I-75 through Manatee and Sarasota counties.
The FDOT is planning a major reconfiguration of this University Parkway I-75
interchange, an alteration with major regional impact on our mobility, evacuation
capability, and economic vitality. There, the FDOT has been planning a DDI, a
“Diverging Diamond Interchange.”
FDOT consultant HDR presented its DDI concept to the MPO CAC and TAC at their
meetings this month. We have posted that presentation to
http://tinyurl.com/bwpges7 . However, that FDOT presentation is not on your MPO
agenda Monday.
Should DDI come up Monday, given the significance of the I-75 University
Parkway interchange, it may be helpful to have at hand some questions and
points that came up at the CAC, and some that could have, in understanding this
unique relatively untested design:
 Though this FDOT SIS project is long into the planning, HDR did not have a projection of
capital and operating cost. SIS $ have priority over $ for Sarasota-Manatee MPO
priorities. Could MPO project funding suffer ?
 The FDOT’s consultant indicated no alternatives to the DDI concept were considered:
 FDOT is currently preparing a manual stating “roundabouts should be
considered in the context of new interchanges and interchange modifications.”
Virginia, Georgia, and other DOTs mandate this practice.
 Sarasota Manatee MPO has on record its policy requiring roundabout study for
intersection changes (#2004-09).
 FHWA Guidance: study roundabout alternatives when using federal funds.
 HDR was unaware of the DDR alternative (Diverging Diamond Roundabout) …
see Institute of Traffic Engineers “Variations on the DDI Concept” Figure 8
http://tinyurl.com/9zakeuw.
 DDI intersections are signalized. DDI is a power-reliant interchange placed here where
hurricane/tornado prone -- knowing the recent reality that wide areas of

2. Louisiana/Arkansas/Mississippi were in hurricane-induced power outage for more than
a week. HDR indicated standby power generators could be used, adding to cost. A
roundabout is not power dependent.
 Safety. A DDI has more conflict points (14) than a modern roundabout’s (8)…i.e. DDI has
a higher crash rate. Signalized ongoing timing adjustments unable to keep up moment
to moment to changing volumes can incent red light running … see FHWA
Memorandum regarding Value of Statistical Life ($6 million per fatality prevented).
Most states use modern roundabouts at interchanges not only for better lower-cost
mobility, but, as well, to relieve dangerous backup from the at-grade intersection into high
speed interstate lanes (as happens today at our I-75 interchanges). Does DDI?
 FDOT has never constructed a DDI. Nor has the FDOT ever constructed a roundabout
interchange. All FDOT interchanges today are signalized. DDI use is recent in a few
states (Missouri/Kentucky/Indiana,e.g.). Modern roundabouts at interchanges are used by
most states and have a longer experience history: notably
Wisconsin/Colorado/Arizona/NewYork/Washington/California/NorthCarolina, etc… thirty examples are
collected athttp://tinyurl.com/9g389cc
Just a CAC rep & a student paying attention ….
Rod Warner
MPO CAC
A Sarasota County Rep
3648 Tangier Terrace
Sarasota, Florida, 34239
941 924 2400
Fax: 942 924 1650
PS. Re the US41 Multimodal Corridor adopted in the MPO’s 2035 LRTP, as a resource of USA mobility best practice
we regularly update these sister websites…
www.US41SimpleTruths.com(US41 from Palmetto to North Port)
www.US41Momentum.com(US41 Sarasota Bayfront & North Trail)
www.SarasotaConnectivity.com(City of Sarasota Mobility).