Tampa I-4/Crosstown Exwy interchange with AET - construction under way

January 27, 2010

In the artsy, historic Ybor City area of Tampa less than two miles (3km) northeast of downtown Tampa construction has begun of the I-4/Selmon Crosstown Expressway Connector. It is in essence  an elaborate interchange between the two parallel highways at a point where they are less than a mile - 1400m or 4570ft (0.86 miles) apart, measuring them from the centerline of each roadway reservation. The driving principle of what looks like a confusing spaghetti of ramps is to anticipate the major movements of this giant interchange and give them their own dedicated roadway.

The old way of designing this kind of project would be to design an interchange at each end. After entering traffic would merge to join a single one-directional roadway, then make the necessary lane changes to diverge on the relevant exit ramp at the end interchange. Not here. The mainline consists of multiple roadways geared to major movements.

Tolling is radically new too and takes advantage of the separate movement roadways to levy separate toll rates.

A huge toll structure will span some 13 lanes of 5 elevated roadways and two ramps to levy highway speed all-electronic tolls (AET) in roughly the middle of the Connector. 

All trips on the facility will be tolled, the toll rates being quite modest since the project is a mix of tax and toll funding.

The project can be granted several firsts:

- first to do all-electronic tolling to help finance an interchange

- first to provide separate trucks-only roadways and ramps

- first new elevated roadway through an artsy historic district for decades

- first time as many as 13 lanes side by side have been tolled by AET

Rationale for the project is that many movements between the two parallel highways were being  served inefficiently and to the detriment of local neighborhoods. Traffic has been using the north-south surface streets, notably N21st and N22nd Streets of Ybor City to make the connection.

The present surface connection along this pair of surface one-way streets involves about ten sets of traffic signals on each.

A fifth of the traffic is truck traffic, much of it moving between I-4 and the port of Tampa, Florida's leading port and located south of Ybor City and downtown Tampa.

Ybor City people in the neighborhood supported the elevated Connector project because it will take heavy traffic off their surface streets.

The elevated is located about eight blocks further east at 30th St close by a CSX rail line so it isn't too intrusive visually.

Zee and Ess and Tee roadways

The secret of the design is to cater to direct interchange movements with dedicated roadways. Thus there are so-called 'Z'-roadways catering to both directions of I-4 traffic west of the connector moving to and from the Crosstown Expressway west of the connector.

So-called 'S'-roadways are the reverse - connecting traffic on I-4 east of the connector going to or from Orlando for example, to the Crosstown west to downtown or beyond.

There are also 'T' movements trucks-only roadways between both directions of I-4 and ramps to and from the busy port area to the southwest. Some of these ramps go another mile from the connector proper.

The project has a minimum of 12 travel lanes, broken at the northern end into 3/3/3/3, each three-laner being either an S-movement or a Z-movement southbound, the others northbound roadways carrying the S-movment and the Z-movement.

In the southern half of the connector the four movements proliferate further as trucks and cars are separated and the dedicated truck roads providing for the T-trips curve towards the port area south of downtown rather than joining the Crosstown Expressway.

Other slip ramps allow more interconnections. But by separating the major movements into dedicated roadways, weaving and merges are minimized.

Everywhere there is full breakdown shoulder to the right of 3.6m (12ft) travel lanes.

The project was designed with alternates of segmental box girder and bulb-T prefabricated concrete beams as well as steel girders. Contractors were allowed to bid the structural method that allowed them to offer the best price.

Steel girder and bulb-T won out with PLC/Archer Western the chosen contractor.

The construction period is three years so completion is due end 2012.

PBS&J were the principal designers of the work.

Planning and permitting began in earnest in 1995 with a first EIS design in 1996. That involved only a 3x3 lane connector. The project steadily grew.

There are 34 lane-miles, or 55 lane-km total in the project as it is being built.


A preliminary tolls schedule puts car tolls at $1.00 for S-moves to or from the east on I-4 and from or to the west on the Selmon Crosstown Expressway, and 50c only for the Z-move to or from the west of I-4 and from to to the east on the Crosstown Expressway.

Other classes of vehicles are charged by the (N-1) axles formula so that a 5-axle tractor-trailer pays 4 times car rate.

T- moves by trucks going to or from the port/I-4 pay a $1.00 toll regardless of their axle count.

Unique AET structure

The all-electronic toll structure is described by an FDOT spokesman as a "unique facility when compared to others on Florida's Turnpike system."

Certainly true.

It looks like a large windowless square section bridge-building of two spans set on three massive towers, one on either side and one in the center of the roadways.  Each of the clear spans is 47m (155ft). They incorporate a steel Vierendeel truss system providing huge space for tekkies movement and electronic toll equipment.

The truss frames will be covered with a neoclassical detailed precast concrete cladding over a cast-in-place concrete frame. Light comes entirely from translucent polycarbonate roof panels. The fabricated steel trusses will be clad with custom aesthetic fiberglass panels with more neoclassical detailing.

Backlit 'SunPass' signs will be fixed to the lead face of each bridge building span.

A spokesman says there is no space at ground level for normal rooms at grade adjacent to a gantry to house servers and readers. She says the project is in Ybor City's red brick historical architecture, an attempt was made to blend in.  

"They are pretty strict down there with their architectural approvals and don't want anything that jumps out as too different.  Those structures also house the elevators that allow the techs to access the gantries in a safe way."

The project is by District 7 of Florida DOT.

Florida Turnpike Enterprise, a division of FDOT will operate the tolling is organizing procurement of the toll systems. A spokesman says that the all-electronic tolling (AET) system will be procured from Raytheon under an umbrella contract for AET on Florida Turnpike projects the company won a couple of years back.

Raytheon has extensive experience in AET, having pioneered the first in North Ame3rica on 407ETR tollroad in Toronto Canada. (ADDITION 2010-01-27 10:00)

ANALYSIS: The overall Connector plan should work well in moving traffic safely and smoothly between the two expressways. Motorists and truckers will get good value for their tolls, and the people of Ybor City will have their quality of life enhanced.

To use the current buzz word the project enhances 'livability.'

Given its capacity and complexity the Connector is quite economical at $650m total project cost ($19m/lane-mile). And its use of all-electronic tolling is a good way of supporting the project.

Contrast this with Caltrans much smaller Presidio Parkway project in San Francisco - also effectively a long interchange - which despite no right-of-way acquisition is costing some $1,045m, (close to $100m/lane-mile) and relies entirely on taxpayers.

No wonder taxes are lower in Florida, and roads less congested.

COMMENT: Architecture is to some extent a matter of personal preference, but the design of the AET bridge on the Tampa connector is an abomination - ugly and absurd. Overhead structures should be as minimal in mass as functionality allows. That is why most overhead toll equipment is mounted on a gantry of some kind.  Gantries are by definition light structures.

This Tampa Connector bridge building is heavy and intrusive way beyond what function requires for all-electronic toll equipment. The neo-classical moldings and wainscoted paneling of the overhead toll building are ridiculous, and have no place on a modern roadway - editor.

NAMING: Here in Maryland the big toll bridge to the eastern shore across Chesapeake Bay is known by everyone as the Chesapeake Bay Bridge, or just the Bay Bridge. The mapmakers also have it named the Chesapeake Bay Bridge. And perhaps because the mapmakers name it that way it just keeps the common name. This despite the fact that for decades the official government decreed name has been the William Preston Lane Jr Memorial Bridge, after a state attorney-general and then governor 1947-1951. The first span of the bridge was gotten under construction during his term.  

Maryland Transportation Authority being a state agency perhaps choose to call the Bridge by its official name. But in deference to comprehensibility they put Bay in parentheses as in William Preston Lane Jr Memorial (Bay) Bridge.

We were asked by officials in Florida to omit reference to Crosstown Expressway and to apply the official name Selmon to the Expressway in Tampa. Selmon it seems was a local football star in the 1970s with a team called the Buccaneers. Our understanding is that the locals, even football fans, still call it the Crosstown Expressway, and Google Maps and Yahoo Maps still have it as the Crosstown Expressway.

Selmon is apparently best remembered locally in the naming of Lee Roy Selmon restaurants dotted around the city.

We'll go by popular names that people know and use, rather than a bunch of politicians notions of what the name should be - editor.

about Ybor City:


on the Connector:


an amazing zoom feature that provides very sharp detail of the plan:


preliminary toll rates and further explanation of the S, Z and T movements in FTE's usual great graphics:


TOLLROADSnews 2010-01-26
ADDITIONS/MODS 2010-01-27 17:00

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