W1-13 truck rollover warning sign

[ACtrafficengr]

How do you calculate the proper advisory speed for the truck rollover sign?

I doubt ball-banking would work, since many trucks will tip at lateral accelerations lower than 0.4, or less than it takes to cause a passenger car to skid.

Thanks!

 

[KRSServices]

The answer lies in the type of curve the truck is going into and generally, it's speed rating. Since the type of loads affect the stability of the unit (ie. liquid vs gravel vs bitumen) I would refrain from posting an actual advisory speed. Posting a speed for the curve, unless it is very conservative, could cause more trouble than it is worth.

If there is a history of rollovers in a particular area, then it would seem that the speed designation exceeds the maximum design speed of the curve, for whatever reason.

KRS Services

http://www.krs-services.com

 

[ACtrafficengr]

The US MUTCD says:

"When the Truck Rollover Warning (W1-13) sign is used, it shall be accompanied by an Advisory Speed (W13-1) plaque indicating the recommended speed for vehicles with a higher center of gravity."

It gives no guidance on how to calculate the required advisory speed.

http://mutcd.fhwa.dot.gov/HTM/2003/part2/part2c.htm#section2C11

 

[KRSServices]

Jim,

Thank you for the link. This document serves as a partial regulatory function and as guideline, and accordingly, it cannot provide details such as the type of formula you are looking for, due to legal issues.

However, section 2C.02 provides your answer, sort of.

It reads:

Standard:
The use of warning signs shall be based on an engineering study or on engineering judgment.

My approach would be to evaluate the geometry of the curve and determine the speed/radius relationship. I was reviewing your question and found a neat little formula that could give you a start anyways. Give me your email address and I can scan it for you and send it to you.

The bottom line however is that the recommendation has to be substantiated by science or judgement. In my area, we have heavy industry and a huge number of vehicles are loaded tankeers, water haulers and tri-axle vac trucks. The guidlines we have used seem to work well.

KRS Services

http://www.krs-services.com