The Red Hill Valley Parkway (RHVP) Judicial Inquiry heard considerable testimony of various witnesses about friction testing. Discussion was had with respect to the testing and results using a Brake Force Trailer, which was described as a standard device and methodology used for the purposes of Ontario’s Ministry of Transportation. Conversely discussion was had regarding testing with the Grip Tester and its results based on a British methodology. The Grip Tester is what was used in the Tradewind Report which became “lost” and therefore the reason for the Judicial Inquiry.
The Inquiry heard testimony from two opposing experts with respect to the appropriateness of using the Grip Tester and British methodology. In order to compare the results with the Brake Force Trailer Dr. Gerardo Flintsch performed some transformations and he testified that these provided a reasonably accurate depiction of the relationship. In contrast another expert, Mr. David Hein, testified that Dr. Flintsch’s transformations were unreliable. This demonstrates the difficulties existing when different instruments are used to document friction and experts claim that one is better than another. Since friction testing for the MOT and municipalities is performed by a very few persons it is difficult for anyone outside of their circle to come to an independent conclusion without having to believe one or the other based on blind faith. Such a predicament should not exist on such an important issue.
Comments were made in a summation report authored by the lawyers representing the City of Hamilton and the importance of two of those comments requires that they be repeated here, as follows:
In Canada, there are no published national or provincial standards or guidelines with
respect to friction measurement or management. There are also no policies or standards
that require or encourage the measurement or management of pavement skid resistance and
macrotexture on road networks or setting friction investigatory or intervention levels.
And secondly:
As discussed further below, FN(90)R=30 is the appropriate lens through which to view the
friction results on the Red Hill. FN(90)R=30 (which will be referred to as “FN30” for
simplicity hereinafter) is an unpublished investigatory level used by the MTO. On that
investigatory level, friction values of 30 or greater measured at 90 km/h with a ribbed tire
on a locked wheel tester are an acceptable friction value. Friction values below 30 may
merit further investigation.
One should ask, in an advanced country like Canada, why are there no standards for “friction measurement and management”? Who would be responsible for creating such a climate of unaccountability? It is not those whose lives are placed at risk who encourage such a development. But those whose responsibility it is to ensure road safety, such as the Ontario Ministry of Transportation (MOT), who would be happy to create an environment where they did not have to be accountable for road surface conditions that do not meet a minimum standard. It is defendants in civil litigation, such as the MOT and municipalities who could be held liable if it was determined that a certain minimum level of friction was not maintained on Ontario’s highways.
The above quote also confirms that there are “no policies or standards” for “measurement and management of pavement skid resistance”. It should not require much imagination that this is also because those whose responsibility it is to conduct measurements and manage roads are responsible for this environment, the defendants, MOT and municipalities in Ontario.
The second quote refers to an unpublished investigatory level. In other words, when measurements of friction are taken there is a level which should trigger further investigation. So why is this level not published? And who is responsible for this development? Once again it has to be the MOT and municipalities who have created this environment. Because if a threshold level was published, and well-known by the public, then the MOT and/or municipalities could be held accountable when a road surface fell below that threshold.
So the second quote refers to this test which is the “appropriate lens through which to view friction results”. Upon operating a Brake Force Trailer through a site at 90 km/h, the MOT states that a minimum friction number of 30 should be attained. What does this “30” mean? Well such terminology changes through the industry suggesting these changes are used to confuse readers. The “30” really refers to 30 per cent of the acceleration due to gravity. In the community of collision reconstructionists this is displayed as “f=.3”. In other words the resultant friction value is 30 per cent of the acceleration due to gravity. By using differing terminology and symbols confusion can be created when in fact there is only one way of referencing friction: only with respect to the earth’s gravitational pull or acceleration due to gravity.
The MOT claims that this “30” is the appropriate level that should commence an inquiry about a road surface. And the participants in the RHVP Judicial Inquiry never questioned whether this value was reasonable because an expert with many credentials testified that this was a reasonable level for investigation. But is it really a reasonable level?
Friction testing has been employed in the collision reconstruction community since the date that someone wanted to know who was responsible for the damages of a collision: essentially for numerous decades. In all these decades collision investigators, whether police, engineers or any collision experts, performed braking tests using their vehicles. The idea is that a set of skid marks are observed at a collision scene and the analyst wants to know how much speed was lost by the vehicle producing those skid marks. So a test is set up by travelling in a motor vehicle over the same surface at a known speed, say 90 km/h, and applying maximum braking while bringing the test vehicle to a complete stop. Thus locked wheel skid marks are produced and their length is measured. This length of skid marks identifies the total speed that was lost and therefore the average rate of deceleration over that time and distance is determined. So this is the friction value that has been discussed above. Over the decades the results of such testing has been presented in courts, throughout the world, and have been accepted. Discussions have been carried out in the collision reconstruction community about peak friction which occurs early in the deceleration as the wheels approach lock-up and the levelling off of that friction when the wheels reach lock-up. And in more current times when attempting to compare vehicles with different braking systems, such as passenger cars with anti-lock brakes versus commercial truck braking, it is important to disable the anti-lock system in the test vehicle so that fully-locked braking occurs. So these tests are purely and fully locked wheel tests which should be similar to locked wheel tests performed using a Brake Force Trailer.
A variety of equipment and testing procedures have been developed over the years by the collision reconstruction community for friction testing. For a number of years investigators developed their own “drag sleds” which they would pull over a road surface and a fish scale would tell them about the frictional force that was generated. This methodology created substantial controversy in the collision reconstruction community as it was argued that the results were unreliable. Others employed “shot markers” that were pointed down at a road surface and the shot would fire paint onto the pavement at the precise point when braking was commenced, thus there was some objective way of knowing the point at which the braking commenced. A variety of accelerometers such as a G-Analyst or VC-2000 began to be used. Now such accelerometers exist on smartphones and can be used to measure deceleration by attaching the phone solidly to a test vehicle. As a result of all this testing tables for friction levels were developed depending on factors such as test speed and characteristics of the test surface. Some of the earliest and best-known work was published by J. Stannard Baker in his classic Traffic Accident Investigation Manual from 1975. A copy of the Baker table of friction is shown below.
The data in the above table is taken from testing that occurred before 1975 and likely as old as the 1960s or older. Note that this table was seen in numerous court exhibits throughout North America for decades. The table contains two columns describing the friction levels obtained on dry and wet road surfaces. So we can see what many collision analysts deemed as reasonably accurate in that historical time. The section for a wet “ASPHALT or TAR” can be examined under four categories: 1. New, Sharp; 2. Travelled; 3. Traffic Polished, and 4. Excess Tar. Under wet conditions it can be seen that the expected co-efficient of friction for testing above 30 mph (50 km/h) was about .45 to .75 on new or sharp surfaces. And for “traveled” surfaces the coefficient of friction was expected to be .45 to .65. And “traffic polished” surfaces were expected to be .40 to .60. So this expectation was from very old testing with old technology cars, tires and asphalt road surfaces. Even the lowest deceleration for common asphalt shown in the above table is at .45. Why is it that, in this era of testing before 1975, it was expected that wet asphalt road surfaces should generate such “high” levels of deceleration? And surely, with over 50 years of scientific study and development we should expect the levels of deceleration afforded in current scenarios to be higher than what existed before 1975.
The point is that the friction levels shown in the above table are not high, they are just substantially higher than the investigative level reportedly used by the MOT. The investigative level used by the MOT is low. And this should have been pointed out during the coarse of the Judicial Inquiry. It may be that the functioning of a Brake Force Trailer reports lower levels of friction than testing with motor vehicles. If so that has not been observed in the testimony of the Inquiry. In whatever manner the Brake Force Trailer functions it must, in some way, be related and representative to the friction achieved by the motor vehicles driven on the RHVP. And there should be an explanation of what that relationship is.
The Inquiry has heard how difficult it is to compare the results between the Brake Force Trailer and the Grip Tester. Does that mean too that there is difficulty in relating the Brake Force Trailer results to what is achieved by typical motor vehicles? The collision reconstruction community has failed to acknowledge that there has to be some variability it the testing of friction from one test vehicle to the next and that has to be accepted. But that variability does not necessarily make the test results invalid for the purposes for which the results are used. The level of variability caused by using slightly different test vehicles has been accepted as minimal consequence in court proceedings.
Those requesting friction testing for the MOT and municipalities must have understood that this variability existed when using common vehicles in any testing. And they likely understood that they did not what this variability to be a factor in obtaining a reliable measure of friction. This is likely why they chose to conduct testing with a specialized instrument such as the Brake Force Trailer. But this trailer must have some valid relationship to the friction demands experienced when driving real-life motor vehicles.
Whatever that relationship is, the reported investigatory level used by the MOT must be viewed as low. Results from testing just outside of the RHVP were higher suggesting that the Brake Force Trailer does not consistently report low friction readings wherever testing is done. The test results along the RHVP were consistently below f=.4 and that should have been a concern, not just because of the values themselves, but because those values occurred on the RHVP which has a high friction demand. The friction demand cannot be effectively reduced just by enforcing a lower speed limit as police cannot be everywhere, 24-7. But there is an inherent friction demand due to the geometry of the RHVP, the short distances between interchanges and the high traffic volumes. This should have been known to the City of Hamilton even before any friction testing results were received.
A final point that has not been addressed during the RHVP Judicial Inquiry is that longitudinal friction is not the only value of importance. The difference in the friction levels laterally across the lanes is also of importance. Vehicular loss-of-directional-control occurs primarily as a yawing action about a vehicle’s vertical centre-of-gravity. That yaw is developed when there are unequal forces operating at the wheels. In modern vehicles those forces are also adjusted by technology such as electronic stability control and traction control. But when friction is substantially different between different wheels because of differences in surface friction across a lane it complicates the issue, sometimes to the point that the surface may have no more friction to supply on one side of the vehicle for the demand that is needed. So knowing the variability of the frictional force across the lanes is an important matter. Measuring the difference in friction within the wheel tracks versus the area just outside of those tracks is important. There has been no discussion noted in the summaries of the testimony that such additional testing was performed.
Similarly the reporting of friction levels as an average over a distance of 500 metres does not always provide the necessary granular detail of importance within that distance. A reporting of the standard deviation of those individual numbers that make up the average can help to provide further information about the characteristics of the road surface. Details like these have not be discussed in the Inquiry’s testimony.
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