Special roundabout in Tobago

Speaking to reporters last week, Dr Furlonge, who is referred to as the “roundabout man” or the “traffic lights man” depending on which Caribbean country you are in, said very careful consideration was given to that area to see what was best suited. Having also been involved in the placement of traffic lights at Lowlands in the vicinity of the Gulf City Mall, he indicated that he does not favour one over the other; instead, he stated that he favours, “what is appropriate for the specific condition and space available”. It is a major/minor intersection he said with the major road being the Claude Noel Highway and the minor road being the Auchenskeoch/Carnbee Road.

There were basically three options available to bring relief on the congestion which normally occurs during morning and evening peak hours. The first was to install traffic signals in order to balance the flows according to the demand in terms of time. Second was the roundabout and the last option was an overpass which was ruled out because the demand is mostly morning and evening and the demand is not significantly high as people generally think.

On the traffic lights option, Dr Furlonge said he did a simulation using real data collected from the intersection and found the results were not sufficiently convincing for such implementation. There were major improvements in the flow from Scarborough to Crown Point and vice-versa, some minor improvements in the right turn from Scarborough to Auchenskeoch, and improvements in the left turn coming out from Auchenskeoch onto the highway. In contrast there was no improvement in the right turn from the Auchenskeoch Road going west towards the Airport.

He noted that the intersection was exceptionally wide as it were and in the past it was expanded to increase traffic flow which created a dangerous situation because now left turn movements in and out from Auchenskeoch were created at high speeds. The intersection prior to the construction of the round-about diagonally was more than 60 metres wide he stated so the intersection could not be reduced therefore it created the perfect fit for the large roundabout with greater capacity than required because of the magnitude of the existing space. That is why a double lane roundabout was designed and constructed at the intersection. “The purpose of an intersection is to reduce relative speed thereby reducing the intensity and level and types of conflicts,” he said.

There are key factors in the design of a roundabout and one such factor is that of conflict. The highest form of conflict is the head-on collision he said. The other four types of conflicts that exist are (i) a rear-end conflict or accident (ii) a right angle conflict, a vehicle coming from the right or light and crossing at a right angle (iii) diverging eg leaving the Highway and onto Auchenskeoch Road and (iv) merging conflict, the reverse to a diverging conflict. Another factor is the flection capability which is a design that shifts the angle and width of entry that forces vehicles to slow down and reducing the potential for collision. The capacity factor allows for efficiency of operations. Dr Furlonge noted that if the Highway were to be converted to four lanes in the future, the design of the round-about will easily accommodate such expansion.

The splitter islands or triangles on the sides he noted were constructed larger than what the designs called for but he said that was a policy decision because Tobagonians are known for driving differently than the rest of the world and one that he does not support. “If you are presenting an international feature of roads it may require a level of re-training and re-education,” he said. The construction of the round-about started on July 23 and was expected to last for approximately ten (10) weeks has seen some delays. It is now expected that the road should be back to full use somewhere around the middle of October. The road is currently being prepared for paving which should be done this weekend after which it will be marked and the entire area cleaned before its re-opening. The project is estimated to cost in the vicinity of $5 million when completed.