Super Roads

[wxfree]

I recently found a description of criteria for a "Mobility Corridor" in Texas.  I'm pretty sure this is the renamed Trans-Texas Corridor.  This makes me wonder about other jurisdictions having official but unused design specifications for what I call "super roads."  Super roads are those contemplated with standards well above existing standards.  Examples of standards for Mobility Corridors include:

design speeds of 85 to 100 mph (with 100 being strongly recommended)
usual and minimum lane width of 13 feet
minimum shoulder of 12 feet, on both sides at all points (including next to speed change lanes)
minimum stopping sight distances vary by design speed, but are all above 1,000 feet
high minimum curve radii
high horizontal clearances - 80 feet for 85 and 90 mph, 90 feet for 95 mph, and 100 feet for 100 mph
median barriers for median widths below the horizontal clearance requirements
ramp design speeds as high as 85 mph (using 70% or 85% of the roadway design speed for the ramps)
single-lane ramp or direct connector lane width of 14 feet, with 8 foot left and 10 foot right shoulders (two lanes would be 26 feet wide with left shoulders at 4 feet)

http://onlinemanuals.txdot.gov/txdotmanuals/rdw/mobility_corridor_5_r_design_criteria.htm  Click sections 2 through 4 to open them.

How many places have official high-standard specifications for roads planners hope to build some day?

[briantroutman]

How many places have official high-standard specifications for roads planners hope to build some day?

I'm interested to hear if any other states actually do, but honestly, I'd be surprised if the answer isn't none. Perhaps an engineer could comment on this subject with more authority, but I haven't seen discussion of 100+ mph highways outside of '40s and '50s gee-whiz mags where stories on "super-highways"  were sandwiched between articles on supersonic airliners and household robots.

[hotdogPi]

How many places have official high-standard specifications for roads planners hope to build some day?

I'm interested to hear if any other states actually do, but honestly, I'd be surprised if the answer isn't none. Perhaps an engineer could comment on this subject with more authority, but I haven't seen discussion of 100+ mph highways outside of '40s and '50s gee-whiz mags where stories on "super-highways"  were sandwiched between articles on supersonic airliners and household robots.

What about straight roads at a constant elevation in plains (so you will be able to see anything within several miles), and no buildings or intersections?

[wxfree]

How many places have official high-standard specifications for roads planners hope to build some day?

I'm interested to hear if any other states actually do, but honestly, I'd be surprised if the answer isn't none. Perhaps an engineer could comment on this subject with more authority, but I haven't seen discussion of 100+ mph highways outside of '40s and '50s gee-whiz mags where stories on "super-highways"  were sandwiched between articles on supersonic airliners and household robots.

What about straight roads at a constant elevation in plains (so you will be able to see anything within several miles), and no buildings or intersections?

I thought about this when contemplating the topic, which is why I used narrow wording.  Many of us have seen roads on which 85 to 100 mph speeds are not excessive on the main lanes (although they often lack the other characteristics of Mobility Corridors).  This is why I asked about official design standards instead of actual operating characteristics.  In the manual, it looks like the highest official design speed in Texas, other than Mobility Corridors, is 80.  My question isn't really about how well roads have been built, but about the enthusiasm of engineers and officials shown by designing and approving markedly higher standards.

[Revive 755]

I'm interested to hear if any other states actually do, but honestly, I'd be surprised if the answer isn't none. Perhaps an engineer could comment on this subject with more authority, but I haven't seen discussion of 100+ mph highways outside of '40s and '50s gee-whiz mags where stories on "super-highways"  were sandwiched between articles on supersonic airliners and household robots.

IIRC, the late 1980's(?) proposals for a tollway between Kansas City and Chicago had a couple of alternatives with speed limits of 85 or 100 mph.  I remember the study specified larger minimum lane widths for the higher speed options ( think it was 13' for 85 mph), and having C-D roadways for all cloverleaf interchanges.

[2Co5_14]

Most state highway departments have such a backlog of current construction and maintenance that it's hard to envision them embarking on a brand new "super-road" building program.  Anytime you increase the design standards, that is going to increase your right-of-way and building costs substantially.

At GDOT, I tend to see the opposite taking place: for example, a lot of 4-lane divided highway projects are having the proposed median widths decreased from 44' to 32' to save money.

My hunch is that engineers are waiting to see what happens with driverless automobile technology in the next 10-30 years.  That may make some of the safety design standards obselete (stopping sight distance, shoulder widths, lane widths, clear zone, etc...)

[wxfree]

Most state highway departments have such a backlog of current construction and maintenance that it's hard to envision them embarking on a brand new "super-road" building program.  Anytime you increase the design standards, that is going to increase your right-of-way and building costs substantially.

At GDOT, I tend to see the opposite taking place: for example, a lot of 4-lane divided highway projects are having the proposed median widths decreased from 44' to 32' to save money.

My hunch is that engineers are waiting to see what happens with driverless automobile technology in the next 10-30 years.  That may make some of the safety design standards obselete (stopping sight distance, shoulder widths, lane widths, clear zone, etc...)

That's an interesting point.  The life span of a new road would likely extend into the era of automated motor vehicles.  When the Trans-Texas Corridor was being proposed, I didn't look at or know about the design manual.  I don't even know if it was online back then.  I don't know how much of the current material was developed for TTC, which was more of a fantasy proposal by toll road companies than a realistic plan, but I figure that's probably the origin of the Mobility Corridor.  Even though we have official design standards, in a way they may be a product of past times, times when traffic numbers could only go up and self-driving vehicles were not considered possible for the foreseeable future.