They "inner bridge rule" cannot be used with a steer axle and the second axle, it can only be used with the second axle and back. This is stated in the federal regulations, and all states are required to abide by the fedral regulations. With the only exception of states that are grandfathered if they had laws where they allowed more weight before the federal bridge law was enacted. Also stated in federal regulations, and Texas is one of the many states that is not grandfathered.
I looked at the Texas regulations and they have the same bridge law as we have in the NW, with one exception. They do not allow more than 80,000 lbs period except with special permit, no matter how many axles. Must be why you guys do not have dump trucks with pup trailers like we have.
And for a single truck the rules are the same as ours, so lift axles would be benificial.
Example my 2006 Kenworth T800:
Has a total wheelbase of a little over 20 feet and a 20,000 lbs front axle with 425 tires. This truck came from Colorado where lift axles are not normally used and for good reason. They allow 20,000 lbs on a single axle as long as the tires are also rated for that, same as bridge law. And for a tandem they allow 36,000 lbs on the interstate, and 40,000 lbs non-interstate roads, bridge law only allows 34,000.
In the NW with only a tandem I could only have a gross weight of 51,000 lbs at my wheelbase. With one lift axle that goes up to 55,500, and with 2 lift axles as long as the inner bridge is more than 11'6" you can carry 60,500.
I went with 2 Watson Chalin super light weight lift axles, 8,000 lbs capacity each. Here is why.
With one standard lift axle I would have added anywhere from 1,300 to 1,500 lbs of weight depending on the axle. So figure 1,500 lbs, I would have only gained 3,000 lbs of extra carrying capacity. With the 2 light weight axles, I added just under 1,800 lbs for both axles and gained 7,700 lbs of extra capacity. And then I could pull a lighter 3 axle pup trailer instead of a 4 axle pup trailer that I would have to pull if I only had one lift axle on the truck. Here we are allowed the max weight of 105,500 for a 8 axle combo as long as the total wheelbase is more than 69 feet. Also another reason for only 8,000 capacity lift axles, is they really only need to carry 5,000 lbs each.
In Washington we don't need a special permit for these weights, but need a continuous "Extended weight permit" in Oregon, and a excess weight permit in Idaho.
Links to bridge law
Texas
http://www.dot.state.tx.us/business/motor_carrier/overweight_permit/permissable_weight.htm
Washington
http://www.wsdot.wa.gov/NR/rdonlyres/46A25D5A-FE56-46BE-AEC6-47CB4BEC072D/0/Legal_Weight.pdf
Oregon
http://www.odot.state.or.us/forms/motcarr/od/8111.pdf
Idaho
http://itd.idaho.gov/dmv/poe/bridgecj.htm
Most dump trucks and pups in the NW are 8 axle combos at 105,500 lbs with either 5 axle trucks with 3 axle pups or 4 axle trucks with 4 axle pups. There are some older 7 axle combos at 101,500 or 102,500 with 4 axle trucks and 3 axle pups. And 3 axle trucks (steer and tandem) with 2 axle pups are relics from the past, usually only used by a small contractor that doesn't need to haul much and is not going to hire the truck out.
I just wish there were the same rules for trucks in all states. Like in California my truck is not really legal and I can not use the lift axles.