Rollover of commercial vehicles

Hello again,

Judging from the time this post has been up without response, I would guess that there are no standard tests. I don't think NHTSA tests commerical vehicles because the private vehicle segment is bigger, and statistcally, more accident prone.

Come to think of it, I drive for a living, and the private sector IS more accident prone, statistics or not!

I read an article in Discover magazine about how they test SUV's for rollover safety specs. I'm sure it's in Discover's archives if you go to their website. Also, National Highway Traffic Safety Administration board itself may be able to help.

I inquired some months ago about finding the center of gravity of a vehicle, and Evelrod gave me a "rule of thumb" way, which he probably explains better than I do. See if you can track him down by e-mail or something.

Hope this helps!

EMc

Wasn't me. I think it was Greg Locock.


Rod

Oo er. I've been here too long, and forgotten the answer!

In England they DO (or did) test some commercial vehicles for rollover potential, by putting them on a big platform and lifting one edge until the vehicle topples.

They may do some dynamic tests as well, akin to the SUV tests, or just on a very large skid pan at constant speed.

Anyway, to a first approximation the important characteristics are the height of the CofG above the contact patch, and the trackwidth. (actually this is a lousy approximation if you've got a flexible chassis or a trailer, or a long travel suspension).

Measuring the height of the CofG strikes me as a tricky process, I'll ask the lads.



Cheers

Greg Locock

The turning radius of the vehicle also comes into play. A vehicle with a tight turning radius will flip easier if the steering wheel is cranked than one with a larger turning rad.

The main problem is people driving an SUV like its a sports car. Physics will always win.

There are a number of common tests for commercial vehicles, which are designed to help determine the rollover threshold. The SAE standard J2180 is a tilt table test for measuring the static rollover threshold. SAE J2179 is a test for evaluating the rearward amplification factor of an articulated vehicle. More recently (2000) ISO 14791 has been introduced with lateral stability test methods.
While one of the most important parameters is the height of the CG, there are a number of factors which affect the dynamic response of the vehicle (suspension, tires, articulation points & type etc).
Currently there are no federal motor vehicle safety standards in the US or Canada which directly regulate the CG height.

Not directly no, but there is a calculation that has to be performed for FMVSS, for light trucks and SUVs, I believe. I think this gives a star rating for rollover, but haven't found the procedure yet. This will be replaced by a proper test, the exact form of which some of us are very interested in. Dynamic rollover testing has proved to be an effective method for terminating employees in the past, so the current bet is that there will be a lot of measurement of wheel loads and a lot of computer modelling (hence my interest). Cheers

Greg Locock

Not sure whether this may be of assistance, but it may help.


054/roadsafety%20conf%20police%20paper_revised.pdf -

Sorry. I was still referring to commercial vehicles when I indicated that there was no current regulation of the CG height. There is considerable research into commercial vehicle rollover being conducted by many agencies, including NHTSA. For example, NHTSA currently has projects in roll stability warning systems, and active braking systems for rearward amplification suppression.

NHTSA has also been conducting a considerable amount of research regarding passenger vehicle rollover. You can check out:

The star rating system can be viewed at:

However, there is not yet a requirement under FMVSS.

Yes, I found the details of the star rating system rather late yesterday. This SAE paper gives a reasonable overview of the topic: 2002-01-0965 (available from for a sum) and rightly emphasises that the star rating system is based on schoolboy physics (my phrase) with little correlation to dynamic stability, as it is based on the ratio of half of the track width to the height of the CG. The website you give says "The Rollover Resistance Ratings of vehicles were compared to 220,000 actual single vehicle crashes, and the ratings were found to relate very closely to the real-world rollover experience of vehicles." If it is as good as that then why are we wasting time and money developing anything better?




Cheers

Greg Locock

I believe UMTRI did some commercial truck rollover stuff in the mid 70's related to Michigan's "double bottom tanker" accidents. You might also check out their articulated vehicle model.
Kevin

Two points: commercial vehicle manufacturers such as Peterbilt and Kenworth do tilt-table testing to determine the point of incipient rollover, and therefore the cg height.

Second, the government's so-called "roll-over ratings" are as Greg says, "schoolboy physics" and are worse than meaningless in the real world. They consider ONLY cg height and track width.
For example, a Corvette has the best roll-over rating according to NHTSA, but per an analysis of crash data done by a writer for Car Driver magazine, the Corvette is something like 187 times more likely to be involved in a roll-over crash than the much-maligned Explorer. And for that matter, the two-door Explorer was 50 times more likely to overturn than the four-door, when both have identical NHTSA ratings.

According to his analysis, roll-over correlated to the number of doors better than to any vehicle dynamics factor.
i.e., a two-door vehicle is much more likely to be driven in a fashion that would produce a roll-over than is a four-door.

Sorry, this doesn't have as much to do with commercial vehicles as you might like. Without a study of the trailer, since most commercial vehicles have semi-trailers, I don't think you could make any meaningful conclusions about comm vehicle dynamics.
And load-shifting is probably more of a factor in roll-overs than any vehicle characteristic you can name.

A seach on TRIS Online (the Transportation Research Information Services search engine) ( looking for "truck stability" came up with these results:


Hope you find something useful!

Sorry, no TRIS doesn't really contribute anything to this topic.
As usual, NHTSA wants to legislate equipment rather than consider that maybe just maybe the driver bears some responsibility for roll-over crashes.
As I hinted earlier, when driver factors correlate to rollovers several hundred times better than vehicle design factors, NHTSA is barking up the wrong tree.

About the only times I've heard of commercial vehicles overturning it has been as a result of load shifting, or falling asleep and running off the road.

Hi,
There is a European standard for rollover of N2, N3 O3,O4 (N=goods; O=trailers)tanks that carry dangerous goods. The standard you require is ECE111. It is very simple, either a tilt test, or a calculation
Del