Little is publicly known about the effects that a rough road surface can have on the motion of a motor vehicle. Gorski Consulting has recently conducted testing with school buses to supplement the growing results of testing already posted to this website on this issue.

On April 5, 2021 an article was posted to the Gorski Consulting website describing the results of testing with a GMC 18-passenger school bus that was conducted on March 4, 2021 on Wharncliffe Road in London, Ontario. At that time we indicated that the results of further testing would be released regarding the same bus as well as testing on March 25 and 26, 2021 with a full-size International school bus. We have now completed analysis of the second round of testing with the GMC 18-passenger school bus and we will present the results in the present article.

In brief, the condition of a road surface is capable of being determined by driving over the surface with a test vehicle while using the accelerometer and gyro sensors of an iPhone accompanied by multiple video cameras. A large amount of testing has been reported on the Gorski Consulting website in the Road Data webpage which confirms this conclusion. Since the testing involved a single passenger car (a 2007 Buick Allure) a reasonable concern is that the data may be different when a vehicle of a different structure and suspension is used. It is fortunate that recently Gorski Consulting has been able to conduct additional testing with two school buses to assess whether the methodology might also be applicable with such totally different vehicles.

The first school bus testing involving a GMC 18-passenger school bus was reported in the previous article of April 5, 2021 entitled “Testing of School Bus Response to Irregular Road Surface Conditions”. We encourage readers to explore this article which can be found on this webpage. This article provided the results of testing on March 4, 2021 on Wharncliffe Road in London, Ontario. The present article will report on the results using the same school bus from testing on March 4, 2021 on Wellington Road in London, Ontario.

The table below shows the results of the Wharncliffe Road testing. Each set of bars represents a time of 30 seconds of travel. As reported previously, a poor road surface would be expected to produce average motions of 0.0500 radian per second or higher. Although several road segments approached this threshold none surpassed it.

The next table shows the results of the Wellington Road testing. An usual occurrence took place when the school bus was northbound on Wellington Road and approaching Hill Street, just south of London’s downtown district. An usually large amount of longitudinal motion took place as indicated by the height of the blue bar shown in the table. The average Longitudinal Rotation was 0.0517 and the Lateral was 0.0345.

The table below shows a closer view of the motions of the bus that took place over that 30 second interval of travel. During this time the bus was travelling at 47 km/h and was slowing to about 28 km/h as it approached Simcoe Street. The largest amount of motion was in a sample of about 200 readings represented by the green oval shown below.

Approximately 200 samples were taken from the motion data and these are displayed in the table below. Again, these data come from Wellington Road between Hill St and Simcoe Street. They reveal the very large effect on the GMC school bus. Within these 200 readings, comprising about 6.7 seconds of travel, the Longitudinal Rotation was 0.0867 while the Lateral Rotation was 0.0435. Thus the Longitudinal Rotation is well above the 0.0500 threshold that indicates a poor road surface. And the Lateral Rotation is just below that threshold.

We visited Wellington Road on April 12, 2021 to examine the surface between Hill Street and Simcoe Street. the photo below shows a view of the northbound lanes of Wellington Road taken from the south side of the intersection with Hill Street. This is approximately where the motion of the school bus began to be excessive. There is nothing particularly obvious about the character if the surface that would signify a problem. Yet watching northbound vehicles one could them bouncing up and down.

The photo below is a view of the northbound lanes of Wellington Road just north of the intersection with Grey Street. Here the surface problems become more visible even though it is difficult to capture such characteristics through photos alone. The curb lane has become sagged, particularly in the area where the left wheels of vehicles would travel.

The next photo shows a northward view of the northbound lanes of Wellington closer to the sagged portion of the curb lane just north of Grey Street. Even though it is difficult to depict the elevation change with still photos, the sagging can still be visually detected.

The next photo shows a view of the same area of Wellington Road but looking southward. Again the dark van is located in the approximate area where the sagging is most prominent. In fact the surface throughout this areas of Wellington Road exhibited similar characteristics.


The purpose of this testing was to explore whether the motions of an 18-passenger school bus could be used to reliably detect road surface problems. We observed large values of motion of the in the data obtained from the iPhone’s gyro sensors. We then travelled to the site where these large motions were detected. By observing the exaggerated motions of passing vehicles, and observing the obvious sagging of the road surface, we confirmed that the motion data made sense. The data was reporting the poor road surface conditions that existed.

This result is not surprising. We have conducted hundreds of similar tests on road segments throughout southern Ontario and the results have been posted on the Road Data page of the Gorski Consulting website. Those tests confirm the reliability of the methods and results.

Further analysis will be reported in the near future from testing conducted with a full-size school bus on March 25 and 26, 2021. We expect  that this methodology will reliably report the motions of this large vehicle. Such large buses have been known to bounce considerably more that passenger cars and light duty vehicles but it will be interesting to see exactly what the data will show.