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Reversing Tampa Congestion

It would be nice to think the Expressway Marty Stone was escorting me down had been closed solely for my visit to Tampa! Having won a Queens Award for export and been presented to her majesty in person – surely I could expect no less! But alas this was not the case, the reason for the closure was the directional change over of the Tampa Hillsborough Expressway's reversible open road tolling lanes.

In 2006, the Tampa Hillsborough Expressway Authority opened the most unique toll road in the world, reversible express lanes. The construction took place above the 20 year old 4 lane divided highway of Tampa's Lee Roy Selmon Crosstown Expressway. The project is the first in the world to combat congestion by combining the innovations of, electronic reversible express lanes, cashless multilane open road tolling (ORT) and all operating on a concrete bridge built in the Expressway median.

During the past 20 years, continued population growth and ever increasing traffic resulted in severe congestion for thousands of daily Expressway commuters. The journey at peak times to commute a 10 mile stretch of Expressway from downtown Tampa to Brandon was as much as 40 minutes. A resolution to this congestion was needed. Building a new green field project or acquiring land was not an option due to environmental issues. So the Authority’s extraordinary solution to relieve this severe peakhour congestion and improve access was to build 10 miles of reversible express toll lanes between Interstate 75 and downtown Tampa. Most of the project was constructed as an elegant segmental bridge and was built using only six feet of space within the existing Expressway median. The aim of the project design was to dramatically reduce impacts on the community and environment, as well as a few cost savings on the way!

The Reversible Express Lanes design stemmed from the results of comprehensive surveys to determine the behavioural pattern of Expressway users, where they went, how they got there and when they travelled. The Expressway Authority received over 2,800 returns from these surveys forming a clear picture of commuter behaviour. The results told that 10 lanes of capacity were required at peak times to cover the road users needs. However, 10 lanes weren't needed in both directions, due to the nature of exiting traffic and their time of travel. This led to the concept of reversible lanes a nonstop Expressway from Brandon to downtown Tampa.

The technologies deployed:
The resulting project was a technological innovation which included the first reversible cashless threelane open road tolling system, a unique approach to video toll collection for customers without transponders and a centralised Traffic Management Center (TMC).

In addition to providing greatly improved daily service to Expressway customers, the Expressway lanes also incorporate features which allow for testing of new concepts in highway safety and operations. The internal dimensions of the bridge are 8ft tall and the weatherproof, hollow core conceals communications, utilities, fibre optics and intelligent transportation systems equipment used for control of the reversible lanes. The design shape of the bridge also had a purpose, it was to limit the view of the bridge so the concrete expanse was more aesthetically pleasing to the landscape and human eye. The beautiful serpentine curves and naves of the bridge mean most of the time your view is of only one side, belying the true vastness of the construction. Another unique feature of this project was the ability for the entire erection process to be done above ground in live traffic including the pillars. The bridge itself was used to bring materials up to the current build location thereby reducing road closures.

Vehicle detection & classification (AVC) in the reversible lanes
 Utilising ORT with no toll booths or plazas eliminates the risks associated with large volumes of traffic slowing down to pay the toll. However, for an ORT system to meet its accuracy levels the AVC aspect becomes a critical function within the bigger picture.

Talking to Vance Williams of Quixote Traffic, the biggest challenge for them on this project was the unique software features and implementation of them. Considerable inhouse testing was carried out to assist with a smooth project integration, this also meant the majority of software questions were ironed out well in advance of any installation taking place. Although the physical hardware was a standard tolling installation requirement, developing the reversible ability of the software took some deliberation in the software code department. Understanding how the AVC system would operate in a forward direction in the morning and then reverse the whole process in the afternoon wasn't as simple as flipping a switch and throwing everything into reverse. The guys class them as 'technical tweaks' but those tweaks enabled the software to shut down and restart in reverse mode. Although two sets of hardware weren't required, two software configuration files were a necessity, one for forward direction and one for reverse. Rules for how Idris reported or responded was another aspect requiring consideration as well as what was actually reported. As an example, in a standard Idris configuration Idris knows the direction of travel a vehicle is moving in, should the direction be in reverse Idris reports this fact as an alarm. However, for Tampa Idris had to determine which direction a vehicle was travelling – forward or reverse, and whether it was the correct direction for the time of day! Once the configuration of rule files and software code was achieved the remainder of the installation was a straight forward build.

There is a time element in all this too, as the purpose of the Expressway is to keep traffic moving. Long periods of lane closure for reversing the lanes would have defeated the objective. This was where using Idris as the AVC provided not only accuracy but time savings too. The whole Expressway is reset and restarted in reverse mode – it's a 'reboot' of the system! This means there is no hardware change over, the process is carried out remotely from the TMC which means the Expressway is operational for about 23hrs a day. Overall it takes just 30 mins to complete a change of direction. The physical change can actually be done in 15 minutes but the extra time is taken for the traffic engineer to drive the route and visually check and recheck that everything is clear and OK.

 Safety is always key to any project and the Expressway is no exception to this rule. The prevention mechanisms for vehicles entering the lanes in the wrong direction are 30 warning gates, 5 impenetrable barriers, more than 40 variable message signs and 25 CCTV cameras. All of which are used to support the traffic managers who oversee the change of direction for the lanes. All the Expressway's ITS operations are controlled from the TMC where the system delivers operational information to Expressway customers and ensures no vehicle may enter the reversible lanes in the wrong direction. In addition feedback is also provided to the TMC operators for the management of incidents or accidents on the roadway. Occasionally the warning gates have been hit by a vehicle trying to access the Expressway from the wrong direction but the barriers are impossible for a vehicle to actually drive through.

The results speak for themselves
This projects design approach has saved huge amounts in capital costs due to the technologies incorporated and the structure and design features used. In addition, by not building interchanges and using slip ramps for access to the new reversible lanes from the old expressway, construction costs were greatly reduced. The reversible lanes are a long term solution to traffic congestion. Its design features the ability to control the traffic entering and exiting the Expressway preventing volume saturation. Prior to opening it was estimated 12,000 people would pay to use the facility at a $1 per time, the actual cost is $1.50 and the Expressway has over 16,000 daily commuters. The trafficcarrying capacity of the existing Selmon Crosstown Expressway has been increased by 150% by the new build and has completely eliminated congestion during peak hours. A journey which took up to 40 mins now takes just 10 mins, and this project has succeeded in sustaining the vitality of Tampa city centre and improving the quality of life for its commuters.

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