ALIGNMENT AND ARTICULATION OF SENGKANG AND PUNGGOL LRT SYSTEM

摘要

The latest people mover system in Singapore, in operation at Sengkang and in construction at Punggol, is a medium capacity Light Rail Transit (LRT) system, aimed at giving modern and quality public transport system for the planned townships. In order to optimise viaduct construction cost, the alignment and structural solution for the system were provided as a single design package. In this paper, the alignment design will be presented in detail with the viaduct articulation described in general. The alignment was modelled on the stringent criteria provided by the train supplier (Mitsubishi) of the D&B consortium. The trains are rubber-tyred vehicles, which travel on a concrete running plinth, assisted by a side guidance system. The alignment design criteria adopted basic principles from rail design. Transition curves are required to provide progressive travelling radius into and out of a horizontal curve. Cant had to be applied to enable a vehicle to negotiate a curve at a designed speed. The limiting horizontal curves and vertical gradients were recommended based on train characteristics and desired operational speeds. The LRT vehicles are adept at manoeuvring steeper gradients and tighter radii. The alignment brief for this project was to accommodate the LRT viaduct, along the road central median, and within LTA's road reserve. In our LRT alignment design along the existing Sengkang roads, the LRT viaduct was designed to closely adhere to the road alignment to reduce remedial road works. The design emphasis for Punggol new town was to integrate the viaduct and road design, since some the Punggol road network planning was still being developed. In some instances, the proposed Punggol road networks were realigned to suit the smoother LRT alignment requirement. In areas where the train negotiates around tight bends, the design considerations encompass the following: adequate horizontal radii to accommodate short pier spans, yet maintaining sufficiently gentle curves so trains can reach desired operating speeds; and reduction of land-take with proper alignment design. Where land constraints existed, the design criteria were pushed to the absolute limit at times, after some initial resistance from the train suppliers. For example, climbing gradients were allowed to occur on transition curves instead of only on straight portions of the alignment, and the gradient was pushed to 6% in some areas. This paper discusses the benefits of a segregated reserve for the LRT viaduct, allowing for more typical viaduct spans.