I would imagine Texas is the best at posting up to their maximum. they have a by-county speed limit set, and many, many rural routes are posted at 70 or 75, as is legislatively defined. It's fairly rare to have a road in Texas that goes through an unpopulated area but has a low speed limit. the only one I can think of is Farm Road 170 in the Big Bend area, which is fairly abandoned, but has a speed limit of 35 most of the way.
FM 170 has numerous curves, one hill with a 17% grade, and many summit curves with restricted visibility, so it is no surprise that it has been zoned for lower speed limits. BTW, I don't remember the limit being 35 for very long distances. The limits I remember are 50 around Lajitas and Terlingua, and maybe as high as 55 for the run into Presidio. There are numerous winding-road stretches with advisory speeds of 40 or lower.
AIUI, before the Gallegos bills were introduced (Gallegos I providing for 75 limits on two-lane roads and Gallegos II providing for 80 limits on Interstates), Texas operated a system where every state highway was considered to have the statutory maximum speed limits for its type, unless it was otherwise zoned by Texas Transportation Commission minute order. The TTC was not empowered to issue speed-zoning minute orders with validity longer than six months. This meant that zoned speed limits in Texas had to be renewed every six months, which I think was typically done by having the commission vote on a new minute order every six months which incorporated all the individual speed limit minute orders by reference.
The Gallegos speed limits work a little differently because they do not alter the underlying statutory maximum speed limits. They only give TxDOT the power to zone
upward (above the statewide maximum limits) by defined amounts in the counties meeting the population thresholds. I am not sure, but I think the Gallegos limits also have to be done by minute order, and if the relevant minute orders are not renewed, then the speed limits go back to the state maxima (of 70, for cars by day) on Interstates and two-lane rural state highways.
What Corco describes is one mode of failure for a special referendum question which simply increases the legislative maximum speed limits--the referendum passes, the power to increase limits is given to ODOT, and the powers are simply not used because there is no duty to do so.
is there anyone else to give the power to? for example, state that "any divided highway with four or more total lanes and no at-grade crossings shall have a speed limit of 80 when it passes through any county with a population density less than X. any undivided highway with no stops for the mainline (traffic lights, railroads, etc) shall have a speed limit of 75 outside of any developed area ..."
The issue is not really one of to whom the power is given, but rather that the power is given to an agency not disposed to exercise it. In principle the power to set speed limits could be given to a nondepartmental board independent of both ODOT and the OTC, but if the right to appoint members of that board were vested in the governor, we would still face the same result--no increased speed limits until Kitzhaber leaves (probably in 2015, bar a successful run for a fourth gubernatorial term).
If ODOT, the OTC, the governor or the legislature tried to pull funny business after a statewide referendum directly voted on by the citizens of Oregon enacting higher speeds, it could put them in a politically and possibly legally precarious situation, and if nothing else, it would thrust the issue of speed limits right to the forefront of Oregon politics.
A successful referendum result would definitely raise the stakes, but I can easily see Kitzhaber taking a stand against higher limits, especially if the terms of the referendum question preserved the existing system of engineering review of speed limits. He would be accepting the risk of being sued or having his legislative allies culled while relying on his personal popularity to ride out the opposition.