Civil Designer road design

Toll Plaza Design Chimes Sweetly For Tolplan Consulting

"Analysing the financial feasibility of toll projects can be quite intricate. To make it easier for all concerned, we developed a financial model for private investors based on the BOT principle; Build Operate Transfer," says Pieter Goosen, Director of the Toll Infrastructure Development Business Unit at Tolplan Consulting in Pretoria. "We also developed a model for state-owned toll plazas so that toll authorities can be sure that the loan is adequately supported by the revenue."

In addition, Pieter developed a model to determine the optimum plaza size based on queuing theory. "It can get quite complicated trying to determine how many lanes are required. Using the model - which is done in Excel - I can input various criteria to calculate the serving time. For instance, a client could specify a maximum queuing length of 6 vehicles + 1 vehicle being served for 95% of the time."

"This model is ideal for different client's specific requirements. Using this model, we can accommodate peak direction flows by designing a proportion of the lanes to be reversible," says Pieter. "This model does give an edge in the market place."

The Karee Toll Plaza 70km north of Bloemfontein is scheduled for completion in March 2003. "The normal design horizon is 30 years with expansion intervals of 8 years. So while this will start as an 8-lane plaza, it will end up with 18-lanes."

"Electronic toll collection is the future for all plazas - on certain toll projects, with overhead sensors as for example in Canada, 95% of all vehicles using the toll road is equipped with electronic tags, so they don't have to stop at all. To cater for this, all the lanes at the Karee plaza will be 3.6m wide with a 1.8m island. The two outside lanes have been stretched to 6.9m, specially for extra-wide vehicles."
  A feature of most toll plazas is the tapering out of the road with a widened section comprising the queuing and lane sections. "This is where Civil Designer came up trumps for us. We used 360 concrete slabs - each measuring 16m2 - to construct the pavement. To assist the contractor, we were able to indicate the levels at the corners of each slab. This translates into real value for the contractor and ultimately to the client."

"Even though the plaza is less than 1km long, the design is finicky. We used Civil Designer to optimise everything. By using all the modules, we were able to check very quickly for service clashes, and to optimise the earthworks to the last cubic meter," says Pieter. "We can show days of apparent savings, but there is still the domino effect on savings, such as the contractor."

"A toll plaza is of course not just a road. We need to design a control building that requires water and sewerage services, and of course storm water must be accommodated. It's almost like a minute township with a lot of detail into a small area."

Plenty of work is in the pipeline as well. "We are jointly undertaking a feasibility study in Kenya with BKS. Projects on the N1, N3 and N4 have all been earmarked for toll plazas in the near future."

The sound of the toll is indeed sweet for Pieter Goosen and Tolplan Consulting.


 
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