A simulator examination of countermeasures to relieve traffic congestion in freeway tunnel sags

Geoffrey William Stuart, Nebojsa Tomasevic, Kristie Lee Young, Timothy John Horberry

Research output: Book/ReportCommissioned ReportResearch


This study examined, using an advanced driving simulator, the nature of driver behaviour around tunnel sags, and to evaluate the impact of three countermeasures on driver speed and braking behaviour in this context. The three countermeasures evaluated included horizontal striped wall markings and two variants of reduced speed limits: (A) where the only the first of the six speed signs is 60 km/h and the remaining are 80 km/h (referred to as Speed Sign 1), and (B) where the first three speed signs are 60 km/h and the remaining are 80 km/h (referred to as Speed Sign 2).The results indicated that restricting speed prior to the downhill section of the sag (Sign 1),followed by an increase in the speed limit markedly reduced braking on this section. This effect was similar when the speed limit was increased near the bottom of the downhill section (Sign 2).On the uphill section, providing cues to the degree of uphill gradient via the use of horizontal wall markings resulted in a slight average speed increase, but the effect was minor. This suggests that misperception of the gradient was not a cause of the speed reduction observed in actual tunnel operations. In conclusion, speed limit interventions in a realistic simulator scenario have been demonstrated to have potential to reduce congestion, and should be trialled in actual operations. Further research is required to understand and design interventions for congestion occurring on uphill sections.
Original languageEnglish
Commissioning bodyTransurban Ltd
Number of pages21
Publication statusPublished - 2015


  • Traffic Congestion
  • Freeway Tunnels
  • Driving Simulation
  • Behavioural countermeasures

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