Speed Limits

Speed Limits

Key Facts:

  • Effective speed management comprises a series of interventions that can have great benefits for road safety; one intervention is the setting and signing of speed limits.

  • Historically, speed limits have been set in accordance with the prevailing speed of traffic. OECD (2006) suggests that this approach is no longer viewed as appropriate; in response, new principles are emerging:

    • Setting speed limits based on an assessment of the combined risk relating to the infrastructure, travel speeds, volume and mix of traffic by type (including vulnerable road users).

    • Setting speed limits based on the safe system principles, meaning that speed limits are set to ensure that when crashes do occur, the resultant crash forces are survivable by most people.

  • In addition, there is a recent emphasis of the notion that speed limits should be credible or self-explaining to encourage self-compliance (DfT, 2013; Van Schagen, Wegman and Roszbach, 2004, as cited in SWOV, 2012; Goldenbeld, Van Schagen and Drupsteen, 2006, as cited in SWOV, 2012; Houtenbos et al., 2011, Lee et al, 2016) and applied consistently across the road network reflecting the function of the road to which they are applied.

  • Even small changes to the speed travelled by the driving population lead to large and measurable changes in risk. A 5% increase in mean speeds typically leads to an increase in injury crashes of 10% and an increase in fatal crashes of 20% (Nilsson, 2004).

  • Meta-analyses show that lowering the speed limit alone by 10km/h leads to a decrease in mean speeds of 3-4km/h (OECD, 2006).

  • To maximize their impact, any changes in speed limits should be accompanied by appropriate enforcement, engineering and educational measures (OECD, 2006; DfT, 2013).

  • Variable mandatory speed limits applied on motorways reduce speed differential and smooth traffic to reduce congestion. Upon introduction to a section of the M25 in 1995 a 15% drop in injury crashes was observed (DfT, 2010). Similar results have been observed across the world. If speed limit compliance is poor, there are several options available that might be used to improve compliance:

    • Clarify speed limit signing and introduce additional measures such as gateway treatments.

    • Introduce engineering measures that have a psychological impact on driver speed choice.

    • Physical engineering treatments that restrict vehicle speeds through vertical or horizontal deflections.

    • Enhance enforcement.

    • Ensure that the road features are safe at travelled vehicle speeds.

    • Educate the public on the importance of reducing their speed.

  • Date Added: 22 Aug 2013, 04:15 PM
  • Last Update: 05 May 2017, 11:45 AM