Do speed bumps really decrease traffic speed? An Italian experience
Section snippets
Introduction, background and purposes of the study
Since early studies were carried out by the Transportation Research Laboratory (UK) in the 1970s (Watts, 1973), the use of vertical raisings of the road pavement as a passive method for controlling the speed of vehicles has become common in many countries (especially in western Europe and North America).
To date, several kinds of these devices have been designed by exploiting the same basic principles, but with the obtaining of different results in terms of effectiveness, discomfort, and
Speed bumps
Speed observations were made in the city of Cagliari (180 000 inhabitants) a middle-size town located in Sardinia (Italy's second largest island).
The Traffic Bureau of Cagliari decided to install speed bumps in 1996 ‘experimentally’ and, to date, there are 30 devices placed on streets with very different geometrical and functional characteristics, but with the common feature of a posted speed limit of 50 km/h. Seven of these locations were excluded from the study, since factors other than the
Speed values at bumps, at related crosswalks and at ‘free’ sections
The overall results of the speed analysis performed in the present study are outlined in the diagrams in the figures Fig. 5, Fig. 6, Fig. 7, Fig. 8, while the number of samples for each analysis or comparison, as well as the mean value of the speed parameters and the ANOVA results, are given in Table 3.
Fig. 5 shows the recorded values of both the 85th and 50th percentile of speed for all sites with tested speed bumps compared with the posted speed limit (50 km/h).
Speeds can be ideally
Discussion
Do really narrow speed bumps reduce traffic speed? Although we are aware that further data must be collected in order to provide a scientifically based answer, the first impression on the effectiveness of these devices is not positive.
As shown by the results, the main aspect to highlight is that the observed speed values at device locations are significantly higher than any other value recorded in similar surveys in the past. We are not able to state whether a real benefit was obtained from the
Conclusions
Italy adopted the use of undulations as a passive speed reduction method only 10 years ago. Ignoring many foreign experiences (especially in UK and US) the only type of device installed was the so called ‘speed bump’, which is characterised by a small width compared with ‘speed humps’, to date widely employed in other countries. The effectiveness of such a device has been assessed by a number of studies, even though transversal size greatly influences the amount of speed reduction achievable
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