THE MAGICAL PROPERTY OF 60 KM/H AS A SPEED LIMIT?
Kloeden et al (1997) found that ?in a 60 km/h speed limit area, the risk of involvement in a casualty crash doubled with each 5 km/h increase in free travelling speed above 60 km/h.? The findings were at odds with previous research and understanding of speeding and the road environment. Hence Lambert (2000) reviewed the Kloeden et al (1997) data, and concluded that the data supports that risk of crashes is best represented by a U shaped curve around mean speeds, with crash risk rising for very low speeds, and for high speeds. It further suggested that the current speed enforcement tolerances are appropriate.
Further analysis shows that Kloeden et al (1997) report must now be considered to be seriously flawed that the analysis:
? Does not support that there are any magical properties of the number 60 as in 60 km/h
? Fails to highlight that outcomes only apply to free travelling speed crashes (about 28% of serious crashes)
? Fails to recognise that a high BAC applies to the whole trip whereas free travel speed applies to only part
? Fails to adjust for the impact of black spots and black links on the findings, and
? Fails to recognise that speed enforcement does not take place at the crash sites included in the study.
This further work supports higher penalties for offences of exceeding the limit by 15 km/h or more provided that enforcement is undertaken close to intersections.