http://goo.gl/maps/oGquMThis interchange is essential to the Strategic Intermodal System (SIS), one of thethirteen (13 ) along I-75 through Manatee and Sarasota counties.The FDOT is planning a major reconfiguration of this University Parkway I-75interchange, an alteration with major regional impact on our mobility, evacuationcapability, 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 theirmeetings this month. We have posted that presentation tohttp://tinyurl.com/bwpges7 . However, that FDOT presentation is not on your MPOagenda Monday.Should DDI come up Monday, given the significance of the I-75 UniversityParkway interchange, it may be helpful to have at hand some questions andpoints that came up at the CAC, and some that could have, in understanding thisunique 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
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/9g389ccJust a CAC rep & a student paying attention ….Rod WarnerMPO CACA Sarasota County Rep3648 Tangier TerraceSarasota, Florida, 34239941 924 2400Fax: 942 924 1650PS. Re the US41 Multimodal Corridor adopted in the MPO’s 2035 LRTP, as a resource of USA mobility best practicewe 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).