“SIG-NABOUT”-the development and trial of a novel junction design

The idea of this new type of junction was first suggested by Kimber and Semmens in 1982. The junction was later named a “SIG-NABOUT” because it combines the features of a SIGnalled junction and a roundABOUT. A junction of this type was tested by the Transport Research Laboratory (TRL) on its test track, with promising results. Simulation techniques also gave an indication of the capacity which could be achieved from such junctions. TRL then looked for support from the Department of Transport (DoT) to carry out a full scale public road trial, to confirm the benefits promised by the necessarily small scale track trial. A suitable public road site at Sefton (near Liverpool) was provided by the North West Regional Office of DoT. The existing roundabout was suffering from considerable congestion in the traffic peak periods, and it was decided to convert it into a SIG-NABOUT. The conversion was completed in 1993. The paper outlines the design and control principles of a SIG-NABOUT and reports on the road trial