Year: 2007-2011

Client: Gammon Construction Limited

Tasks: Traffic Survey, travel time survey, detailed design and road diversion plans road safety review, develop microsimulation models for the road diversions

Woodsville Interchange has long had traffic congestions and delays because of its inherent design flows. To ease the conditions, the authority embarked on an expensive scheme to grade separate some of the busy arms. It involved a three-tier road, a viaduct and two tunnels construction at a very busy and complex 6 arm interchange within the urban and strategic location in Singapore. The condition was further complicated with an existing MRT line beneath the construction site. To create space for the tunnels work site, major changes had to be made to the existing interchange layout whilst maintaining pedestrian connectivity along all roads at all times. Several options were developed and discussed with the authority. The best option Ali developed was a gyratory system that at first the authority did not accept, worried about traffic escalation and long delays. However, this option was tested carefully using VISSIM microsimulation and immediately the benefits were realised. Not only it showed smoother traffic movements throughout construction stages, the greatest benefit was to eliminate multi staging of road diversion schemes that would have been costly, time consuming and deteriorated traffic congestions as showed in VISSIM microsimulation. Before and after the scheme, travel time, delay time and traffic count survey were carried out and as indicated, traffic condition was improved during construction than before work started. In fact, with increasing traffic growth the system worked well during construction period to the extent LTA opted for this scheme to be a permanent layout after construction work was completed.
Once the construction work started, Ali conducted detailed design road safety review for the new tunnels. The new viaduct and the permanents roads leading to and within the interchange. During construction stage, Ali also conducted road safety review for each stage of road diversion until the gyratory system was built.
Ali and his team received LTA commendation for the innovative idea of gyratory system that solved the current traffic problems in this area and served as the best road system for the permanent situation. Perhaps if the gyratory road system was built first, there was no need for the construction of tunnels and the viaduct. Later, in a discussion with the project director, it was agreed that this large-scale construction work could have deferred to year 2020 if LTA knew in advance about the gyratory system benefits.