Why would milk tank trucker's want a short (28') inner bridge length?

Hello To All -

By way of introduction, I am a Research Engineer with the University of Texas - Center for Transportation Research. I have posted questions on the TruckerReport forum before regarding truck size and weight questions when I could not find help anywhere else (and nothing could be found in publication).

I am currently working with other researchers to evaluate a proposed Texas State Legislature House Bill (HB 3129) to increase the allowable gross vehicle weight for milk tankers to 90,000 lbs. The bridge and pavement analysis will be straight forward. However, there is a special exemption currently in state statutes that allows a milk tanker to operate with an inner bridge length of 28' or greater (36' is legal in Texas) as long as the trailer and drive tandems are carrying 34,000 lbs each. Likely this would change if the 90,000 lb Bill is passed.

However, though I have searched all of the literature I could find on the subject and have stopped to talk with Western Dairy Transport operating out of Windthorst Texas - I have not yet been able to find out or understand how a milk tank trucker could benefit from a shorter inner bridge length. It seems this would reduce the capacity of the milk tanker, unless a larger diameter tank was used. Most of the tank trailers I've seen are around 6,000 - 6,400 gallon capacity which would be roughly 51,000 lbs - 55,000 lbs of milk. I haven't seen any milk tank trailers running in Texas that seemed much larger in diameter than the typical tank trailer units (Polar, Tremcar, Burch Tank and Truck, or Paul Mueller for example) or appeared to have a shorter inner bridge length.....though perhaps these are used in certain parts of the state. I don't get to El Paso or Amarillo that often for example..........I think Fresh Dairy Delivery is out of El Paso and WDT is out of Cabool, Mo though I see their trucks all the time on IH 35 in Austin; other milk tankers I've seen Texas Highways over the years are Lone Star Milk Transport, Southern Food Groups (Dallas) Winburn, Leibham, GH Processing (Arizona), Mountain Milk Hauling, Carpenter's Milk Service, and others that escape my mind right now.

Can you help me understand if a 28' inner bridge exemption is of any use? Is this perhaps an old exemption that made sense decades ago, but is no longer in use though it is still on the books? One of the frustrating aspects of researching these issues is that the history of why certain rules, code or laws were passed is not retained and the people involved have retired long ago.

Any help you can give will be much appreciated,

Thanks very much,

Mike

 

mnmover - Thank you very much for your replies. Actually, I am familiar with the Specialized Hauling Vehicle (SHVs) configurations in Minnesota and we considered including a 5-axle straight truck - steer, plus fixed tandem and 2 air liftables. However, milk haulers don't currently run these configurations in Texas and in any case, this unit would not be able to operate at 90,000 lbs.

The American Association of State Highway and Transportation Officials (AASHTO) Manual on Bridge Evaluation now includes bridge load configurations for SHVs with 4, 5, 6 and 7 axle configurations. Either pusher, tag or booster axles are considered. However, the assumed liftable axle loads are capped at 8,000 lbs per axle which might or might not be the actual weights that are applied depending on how the axles are adjusted.

It appears that maneuverability is the main reason for the shorter inner bridge length as mentioned by passingthru69 and neverready.

I've been to Minnesota and Michigan and have seen the caterpillar rigs and other specialized trucks that operate in the 'frozen four' ----- the combination of heavy trucks and harsh winters likely creates very difficult design problems. I've visited the MnRoad project near Albertville on I-94 during its construction ----- this project has really paid off for Minnesota and the nation....lot's has been learned.

Thanks again for your help. I would appreciate comments from other milk haulers.

Mike