Are some speed bumps too aggressive? Are all speed bumps created equal”? Testing by Gorski Consulting provides some answers.

Everyone has ridden through various traffic calming including speed bumps designed to slow down traffic. However there is no publicly available data on features such as speed bumps that can indicate whether they are appropriate or needlessly too aggressive.

As part of the road assessment work conducted by Gorski Consulting, testing was recently completed on Edmonton Street in London, Ontario, Canada.

View, looking north, along Edmonton Street in East London, Ontario where testing was conducted to determine the aggressiveness of its speed bumps.

A test vehicle was ridden over a series of 5 speed bumps. The vehicle was instrumented with an iPhone that documented the vehicle’s longitudinal and lateral rotation. This is similar to the work that has been previously done and reported in the Road Data page of the Gorski Consulting website.

An example of the rotation data is shown in the chart below.

Example of the rotations of a test vehicle caused by travelling over a speed bump.

The above chart plots the motion of the vehicle over a  time of just 2 seconds. The test vehicle’s speed was 28 km/h or 2 km/h slower than the 30 km/h speed advisory sign posted on the roadside. The results show that most motions are completed in about 1 second. This is shorter than other road features such as road repairs which are typically longer along the length of a road.

The testing was performed in a northbound direction and then the vehicle was turned around and the testing was repeated in a southbound direction. The following represents the data that was obtained. The rotations are expressed in radians per second. One radian is equal to 57.3 degrees.

Northbound, 1st speed bump, 24 km/h
Longitudinal Rotation Rate = 0.1795
Lateral Rotation Rate = 0.0757

Northbound, 2nd speed bump, 29 km/h
Longitudinal Rotation Rate = 0.2669
Lateral Rotation Rate = 0.0911

Northbound, 3rd speed bump, 31 km/h
Longitudinal Rotation Rate = 0.1846
Lateral Rotation Rate = 0.1309

Northbound, 4th speed bump, 31 km/h
Longitudinal Rotation Rate = 0.2064
Lateral Rotation Rate = 0.0909

Northbound, 5th speed bump, 30 km/h
Longitudinal Rotation Rate = 0.1446
Lateral Rotation Rate = 0.0935

Southbound, 5th speed bump, 29 km/h
Longitudinal Rotation Rate = 0.1528
Lateral Rotation Rate = 0.0407

Southbound, 4th speed bump, 31 km/h
Longitudinal Rotation Rate = 0.1875
Lateral Rotation Rate = 0.0509

Southbound, 3rd speed bump, 30 km/h
Longitudinal Rotation Rate = 0.1306
Lateral Rotation Rate = 0.0743

Southbound, 2nd speed bump, 30 km/h
Longitudinal Rotation Rate = 0.1681
Lateral Rotation Rate = 0.0508

Southbound, 1st speed bump, 28 km/h
Longitudinal Rotation Rate = 0.1300
Lateral Rotation Rate = 0.0786

Comparisons can be made to the previously reported road data shown on the Road Data webpage as well as in discussions in a number of previous articles uploaded to the Gorski Consulting website. We have observed that a road surface that is in good condition will cause rotations in the range up to 0.0200 radians per second or less. A roadway of average quality will produce rotations between 0.0200 and 0.0500 radians per second. Rotations above 0.0500 radians per second indicate a poor road surface. However these general recommendations are based on averages typically taken over about 30 seconds of testing and often at speeds of 80 km/h. During those longer distances the effects of individual depressions are masked by being averaged along with the smoother portions of the road. So the values are not directly comparable to the present data. However these numbers can provide some instruction for comparison.

A closer comparison comes from tests on road surfaces where there has been some repair work and then a patch has been applied to the pavement which is uneven and often depressed. Thus we have referred to such depressions as “incomplete road repairs” because the final filling in and leveling of the patch has not been completed. This data has been reported for shorter times of only 2 seconds while the vehicle travelled over the road repair. Thus such data is more comparable to the speed bump data which is also reported over time of 2 seconds. This data can  be found in the Road Data webpage. As a comparison, the worst incomplete road repair we have documented was at Vancouver Street near Whitney Street in the spring of 2014. Results of the lateral and longitudinal rotations from that testing are shown below.

Vancouver St at Whitney St; Northbound

Speed     Lateral     Longitudinal

30         0.1207      0.1895
29         0.1190      0.1741
28         0.0692      0.1647
26         0.1361      0.1957
25         0.1390      0.1868
24         0.0578      0.1606
25         0.1408      0.1811

Vancouver St at Whitney St; Southbound

32         0.1656      0.7545
25         0.1162      0.3288
25         0.1208      0.3562
18         0.1396      0.1938
22         0.1315      0.2828
20         0.1336      0.2546
22         0.1492      0.2857

It can be noted that in the first southbound test on Vancouver Street the test vehicle was driven at 32 km/h over the depression and this resulted in the front underside of the test vehicle making contact with the rising edge of the pavement as the vehicle was exiting the depression. A view of the depression is shown below.

View of an 8-foot carpenter’s level placed in the depression of the road repair on Vancouver Street in the spring of 2014.

The resultant damage to the underside of the test vehicle from striking the road surface is shown below.

View of the underside of the test vehicle showing asphalt clinging to the metal where the contact occurred.

As can be seen in the data above the impact resulted in a reading of the Longitudinal rotation of 0.7545 radians per second! This is equal to a rate of 43.2 degrees per second. Such an impact could easily set off the test vehicle’s air bag and possibly cause injury to the driver, particularly if the driver was out-of-position. So road conditions that cause contact with the underside of a vehicle cannot be taken lightly.

The photo at the beginning of this article shows one of the speed bumps on Edmonton Street that contains several scrapes from strikes by the underside of passing vehicles. Similar scrapes were also found on several other speed bumps on that road. So it becomes questionable whether the speed bumps may be too aggressive. This is a question that needs further study and this is the purpose of the Gorski Consulting testing.

There are a variety of public discussions about road surface conditions. The Canadian Automobile Association (CAA) provides an annual “Worst Roads Campaign” which asks the public to submit their opinions as to what they believe are the worst roads in their area. The CAA then provides this data to the news media who then publish or broadcast the results. While such a campaign may be well intentioned it is unscientific. There is no way to know whether a particular road obtained the “worst” rating simply because enough respondents happened to make their complaints without being able to compare the road to others. This is simply a subjective process. It may be harmful if too much publicity is placed on repairing a particular road when another one of worse quality is ignored. So there is a reason why objective data is needed so that the quality of road surfaces and features can be compared upon a scientific basis. Unfortunately those who maintain the roads, such as various municipalities and provincial government, are resistant to releasing their data on the quality of their roads for fear of that data being used against them in civil suits. Thus the data from the Gorski Consulting website is the only information that is objective, independent and publicly available. The Road Data webpage provides information about the motions caused by a wide variety of roads and road features including railway tracks and bridge junctions. It is expected that the new data from Edmonton Street will be added to the Road Data webpage in the not to distant futur