Do speed bumps really decrease traffic speed? An Italian experience

doi:10.1016/S0001-4575(00)00070-1

Accident Analysis & Prevention

Volume 33, Issue 5, September 2001, Pages 585-597

https://doi.org/10.1016/S0001-4575(00)00070-1 Get rights and content

Abstract

Italy introduced the extensive use of speed bumps only in 1990, in an attempt to limit the high number of fatalities involving pedestrians in urban streets caused by the high speed of vehicles. In many countries, such devices have been the subject of careful investigations (in order to assess their effectiveness and disadvantages for the traffic circulation) and this has resulted in a number of modifications in the design to improve their performance. On the contrary, no systematic and scientific studies have been carried out on Italian installations: moreover, the type of undulation adopted is known to produce a series of problems for some categories of users and is not so effective in reducing speed as larger devices such as ‘speed humps’ or ‘speed cushions’. This paper proposes a study of the effectiveness of 23 speed bumps installed in the city of Cagliari; to this aim, a speed analysis was performed at speed bump locations, at the crosswalks protected by the devices and at sections of the streets where bumps are installed but far from them. The results show that in one third of the cases the 85th percentile of speed measured at the speed bumps is higher than the posted speed limit (50 km/h) and an equal percentage of vehicles travel at a speed in the range of 45–50 km/h. No statistically significant differences were found from the comparison of speed values observed in free, bump or crosswalk sections of the same streets, while speed profiles calculated at four sites, where a high percentage of braking vehicles was observed, showed a common trend from which it clearly emerges that the effect of the device on driver's behaviour is restricted to a short spatial range (about 20–30 m before and after the bump). The current situation thus suggests the use of more effective devices such as humps or cushions, or the integration of speed bumps with other traffic calming techniques.

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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The analysis of speed profiles reveals an MAPD value of 13.70% indicating that SCS exhibits speed reduction capabilities comparable to traditional speed bump. In terms of discomfort, the VDV for two wheelers passing over a speed bump is measured at 5.92 m/s^1.75, whereas the VDV for SCS is found to be 5.16 m/s^1.75. Similarly, the Static Compressive Stress (S_e) experienced at a speed bump is 0.60 MPa, in contrast to the 0.33 MPa recorded for SCS. This data underscores a noteworthy 12.8% reduction in VDV and a substantial 45.57% reduction in S_e.
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Citation Excerpt :
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