Speed Bump Aggressiveness As Part of Collision Cause Analysis

Motor vehicle collisions are caused by many factors including the characteristics of a road surface. Vehicle reactions to speed bumps can lead to understanding how uneven road surfaces can cause collisions. The following is an example.

At approximately 0330 hours on Sunday, October 26, 2019, a Mercedes vehicle was northbound on Wilson Ave, just west of downtown in London, Ontario. Upon approaching the T-intersection with Blackfriars Street the vehicle went out of control. It knocked down two utility poles, then struck a commercial building on the west side of Wilson, it was then deflected and impacted a residential house on the opposite side of the T-intersection. News media reporting on the collision described the site as a “war zone”. A woman sleeping in the struck residence was lucky to escape injury as a neighbour reported that “Her head was a couple of feet from where the car stopped”.

The Google Maps view below shows the full length of Wilson Ave between Dundas Street to the south and Blackfriars Street to the north. The area of impact is located at the very top edge of the view denoted by the caption “Society Cafe”.

Gorski Consulting attended the site on October 28th and the following images provide some detail to the amount of carnage that occurred about 36 hours earlier.

Looking from a distance south of the impacts we were able to detect a loss-of-control tire mark that demonstrated that the Mercedes rotated counter-clockwise on the road before travelling onto the west roadside. Two photos below contain orange arrows that identify the location of the “yaw” tire mark.

Backing up further to the south we observed the location of a speed bump on Wilson Ave. Using Googlemaps we estimated that the bump was located about 154 metres south of the intersection with Blackfriars, or about 126 metres south of the first struck utility pole.

When we walked further to the south the photo below shows that the yellow warning sign can still be seen however a truck and trailer was parked on the east side of Wilson and the following photo, taken from further to the south, shows that the warning sign is no longer visible as it is blocked from view by the parked vehicle.

Further examinations revealed that there were four speed bumps located along the approximate 725 metre length of Wilson Ave from Dundas Street through to Blackfriars Street. It could not be expected that a northbound driver could be oblivious to the presence of all these speed bumps even though some of the warning signs might have been blocked from view. However there was no information made available whether the collision-involved Mercedes travelled the full length of Wilson or if perhaps the vehicle turned onto Wilson from one of the crossroads. Thus it is possible that the driver might have experienced a couple, or even just one of the speed bumps before experiencing the loss of control.

There is no question that the collision-involved Mercedes was travelling very quickly, and likely at highway speed along a narrow residential street posted with a maximum speed limit of just 50 km/h. So why did this occur? If the driver was familiar with the roadway then he/she should have been aware of the presence of the speed bumps. And one would expect that any driver would find it uncomfortable to travel over a speed bump at highway speed. Any driver can appreciate that a speed bump is designed to discourage high speeds and that driving over a speed bump at high speed should have a major effect on the motion of the vehicle and its control. But how much objective knowledge is there other than a subjective opinion or conclusion? And what if a vehicle travelled over a road surface feature that was similar to a speed bump but not designed to be there? For example a depression in a road surface might cause a similar disruption to the motion of a vehicle. But what objective data exists about the effects that this might have on the control of a vehicle and the possibility that it might cause a collision?

A few years ago, as a result of a civil suit, Zygmunt Gorski was part of a team of experts that came together with an opposing team of experts whereby a decision was to be hammered out whether a road surface “undulation” or depression had led to the loss-of-control of a vehicle on a rural highway. The collision led to massive injuries to two vehicle occupants. Hundreds of thousands of dollars were paid out in consulting fees just from the experts, not including the lawyers fees. Several meetings of the experts were arranged by the court and a mandatory report of our findings was to be prepared. In the end essentially nothing useful was developed as even the most basic terms and beliefs could not be agreed upon by the experts. None of the experts could present basic data on the effects that a road surface bump, depression or undulation might have on a vehicle. Essentially there was no such data. In the realm of civil suits such data is often hidden by both sides for strategic reasons. And the costs of conducting laser scans or employing road surface profilers prohibit the development of useful data except in a few high-cost cases. A simple instrument, following a simple procedure, and low cost, could be helpful, not only in court proceedings but in educating the public about how the characteristics of road surfaces can effect vehicle motions.

These are some of the reasons why attempts have been made by Gorski Consulting to develop some objective data to answer this question of the relationship between road surface conditions and collision causation. As mentioned many times in previous articles, a Road Data file exists on the Gorski Consulting website which contains a list of all the sites throughout southern Ontario where testing has been performed. Several articles have been posted on the Gorski Consulting website describing the testing procedures and the meaning of the results. Some testing has involved very short road segments where the test vehicle has crossed over bridge junctions, railway tracks, incomplete road repairs and speed bumps.

With specific relevance to the Wilson Ave collision, in 2018 Gorski Consulting conducted some testing on a set of five speed bumps located on Edmonton Street in London, Ontario. These bumps were selected because of the subjective sensation that they caused overly large reactions of vehicles passing over them. Views of the Edmonton site are shown below.

In the 2018 testing a 2007 Buick Allure was driven at approximately 30 km/h in both north and south directions on Edmonton Street and the motion of the vehicle was documented as noted in the table below.

The data from the above table is shown in the chart below.

In an article (“New Test Data of Speed Bump Aggressiveness”) discussing the testing, published on July 2, 2018, a table erroneously reported the Longitudinal Rotation during the northbound crossing of the 2nd Speed Bump as 0.2669 radians per second. This error has now been corrected in the above table and chart to correctly read 0.1758 radians per second.

On May 18, 2021 we conducted further testing at the Edmonton site using a similar procedure. However we used a 2012 GMC 18-Passenger School Bus in the new testing. The results from this new testing are shown in the table and chart below.

Further testing was also conducted on May 11, 2021 using the same GMC school bus but along a different route in London, Ontario.  The route followed Cranbrook Road, Vicount Road and Farnham Road. The route is shown in the Googlemaps view below.

A table and chart from the May 11, 2021 testing are shown below.

Further testing was conducted along Wilson Street on May 25, 2021. The same 18-passenger school bus was driven northbound and southbound over the four speed bumps at the same speed (30 km/h) as the other two sites. The results from this testing are shown below, with tabular form, and also as a chart.

Discussion

The results from the four testing sessions can be summarized for the average Longitudinal and Lateral motion:

2018 Edmonton: Longitudinal = 0.1660, Lateral = 0.0777

2021 Edmonton: Longitudinal = 0.1654, Lateral = 0.0933

2021 Cranbrook: Longitudinal = 0.1495, Lateral = 0.0474

2021 Wilson: Longitudinal = 0.1922, Lateral = 0.1018

What stands out in these values in that the speed bumps on the Edmonton Street site produced higher levels of motion than the Cranbrook Road route. The school bus driven on the Edmonton site in May of 2021 experienced a higher level of lateral rotation than the Buick passenger car used in the 2018 testing. So we would expect that finding to continue on the Cranbrook site which was also driven by the same school bus. Yet we see a greatly reduced level of lateral motion of the school bus (0.0474) on the Cranbrook site.

Next, we see an even larger effect on the school bus at the Wilson Ave site. Both the longitudinal and lateral motions of the school bus were higher than at the Edmonton and Cranbrook sites. This effect has to be related to the difference in the speed bumps and not due to the characteristics of the school bus. Or, possibly, that the characteristics of the school bus, such as the track width and wheelbase, interacted with the differences in the speed bumps to cause the end result.

Since the Mercedes was northbound when it passed over the 4th Speed Bump on Wilson Ave, we can take a closer look at the individual samples over the 2-second interval from the testing that was conducted on May 25, 2021. This data is shown below.

What should be obvious in the above graph is that the peak longitudinal rotation and the peak lateral rotation occurred a the same time. And both of these peaks are quite high (over 0.5000 radians per second). Not only was the front end of the bus lifted but the bus was also rotated sideways at the same time, in a very short time frame of about a 1/3 of second (approximately 8 samples). Very short vibrations with high peaks can be irrelevant however this time of about 350 milliseconds is long enough to be of relevance.

This is an example of a single result and if the bus was driven over the same speed bump several times we might get quite different results. However this fact is educational in that it demonstrates that vehicles reactions to the same roadway features may be different from one instance to the next. When an investigator conducts one or two tests it is likely that the full range of possibilities may not be demonstrated in the data. Closer consideration is needed before drawing a conclusion whether a roadway feature may have contributed to a loss-of-control collision.

By performing these tests we are developing more and more data that is becoming useful in understanding what is important in evaluating the road conditions that effect a vehicle’s motion. It can be noted what we have not conducted any measurements of any of the speed bumps in this testing. Nor have be conducted any measurements of any of the other roadways on which our testing has been conducted and reported in the Road Data file contained in the Gorski Consulting website. This testing simply involves an examination of the reaction of a motor vehicle to the road characteristics.

The usefulness of the procedures discussed here is in their simplicity and cost effectiveness. The performance of any road can be evaluated by anyone who possesses a smartphone such as the Apple iPhone. No specialized equipment is needed. A couple of video cameras are needed but these can be purchased at very low costs. Through training and experience anyone can  examine the results of their testing and be able to determine, in a objective manner, whether the characteristics of a road may have contributed to a motor vehicle collision.