When interstate highways are built with federal funds, it is my understanding that the construction must adhere to strict federal engineering guidelines - width of roadbed, grade, curvature, speed limits, separation of lanes of travel, and such. In the history of the interstate system only two road segments that I know of have been granted waivers to these rules: 1) I-70 through Glenwood Canyon in Colorado, and 2) I-93 through Franconia Notch in New Hampshire. I am only familiar with I-93 where the highway becomes an undivided parkway dropping from two lanes in each direction to one. The speed limit also drops from 65 mph to 45 mph. My questions are:
Where can I obtain a copy of the engineering guidelines governing interstate highway construction?
How do states apply for waivers and what qualifications must be met? I know that I-93 got a waiver in large part to preserve the unique character and historic locations within the notch. Surely there must be more specific rules.
Have any other waivers been granted? What waiver applications have been denied in the past?
On what basis did I-70 in Glenwood receive a waiver?
(1) Glenwood Canyon’s spanking new I-70, completed in 1993 at a cost of $40 million per mile, was the last major link to be completed in the Interstate highway system, and AFAIK meets all the criteria for an Interstate (see below).
(2) All the maps I can find on the Web, including this one, show that the Franconia Notch Parkway is decidedly not part of I-93; it is U.S. Highway 3 and it connects two sections of I-93.
You can obtain a copy of “A Policy on Design Standards - Interstate System” (publication code D-4) for $12.00 at the AASHTO bookstore, if you’re morbidly curious.
You might also find this DOT page to be useful. It provides some basic standards that Interstates have to meet:
It also states that, as of the end of 1998,
This includes two sections in Ohio and one each in CA, DC, MA and PA.
Frankly, I can’t tell anything by that map. My DeLorme Atlas of New Hampshrie shows that I-93 and U.S. Route 3 are the same road through the notch. This page has a photograph of the signage to prove it. See also this map
I-93 and Route 3 coincide for the trip through the notch. I-93 was overlaid on the path of the older State Route 3 when it was constructed through the notch in the 1980’s. On local maps this difference is shown subtly, using the interstate highway graphic through notch with the standard state route graphic ont eh outside. The map you linked to is a poor representation. I travel through the area routinely, and I can assure you that these details are accurate. Besides, I just finshed doing some research on the construction AND watched a documentary on the subject. (I’m a bit of a history buff on the region).
As to Glenwood Canyon, it’s waiver was mentioned in the documentary I saw about Franconia Notch demonstrating the difficulties involved in deviating from the standard on federal highway projects. Later, I spoke with a park ranger about Glenwood Canyon. He didn’t know the specific details of the waiver, but confirmed that it too had special project considerations. After doing some research on the internet I believe I-70 deviates from the spec on curvature and the narrow width of its roadbed. In fact, warning systems have been installed to alert drivers about these severe driving conditions due to abnormally high incidences of rollovers. There is some information about this in the Nov/Dec 97 issue of Public Roads Online. I don’t know how the hanging bridges and the tunnels affect I-70’s status since I haven’t read the specifications yet.