TRAFFIC BASIS

Each section of interstate highway shall be designed to serve safely and efficiently the volumes of passenger vehicles, buses, and trucks, including tractor-trailer and semitrailer combinations and corresponding military equipment, estimated to be that which will exist in the design year which hereafter is to be 20 years beyond that in which the plans, specifications and estimates for actual construction of the section are approved, including attracted, generated, and development traffic on the basis that the entire system is completed.

The peak-hour traffic used as a basis for design shall be as high as the 30th highest hourly volume of the design year, hereafter referred to as the design hourly volume, "DHV." Unless otherwise specified, DHV is the total, twodirection volume of mixed traffic.

CONTROL OF ACCESS

On all sections of the Interstate System, access shall be controlled by acquiring access rights outright prior to construction or by the construction of frontage roads, or both. Control of access is required for all sections of the Interstate System, including the full length of ramps and terminals on the crossroad. Control for connections to the crossroad should be effected beyond the ramp terminals by purchasing of access rights, providing frontage roads to control access, controlling added corner right-of-way areas, or denying driveway permits. Such control should extend along the crossroads beyond the ramp terminal about 100 feet or more in urban areas and about 300 feet or more in rural areas.

RAILROAD CROSSINGS

Railroad grade crossings shall be eliminated for all through traffic lanes.

INTERSECTIONS

All at-grade intersections of public highways and private driveways shall be eliminated, or the connecting road terminated, rerouted, or intercepted by frontage roads. Exception may be made to permit intersections at grade in sparsely settled rural areas which are a sufficient distance from municipalities or other traffic-generating areas to be outside their influence, and where all of the following conditions are satisfied:

(a) The Interstate highway has a DHV of less than 500.

(b) The intersection at grade is with a public road or private driveway with little potential for traffic increase and on which the current ADT does not exceed 50 vehicles.

(c) Such intersections do not exceed two per mile of the Interstate highway.

(d) At the time of initial construction additional right-of-way is obtained or controlled so as to permit the ultimate construction of an interchange in place of an intersection with a public road. (e) The right to eliminate, terminate, or reroute each private driveway that intersects at grade with an Interstate highway is vested in the appropriate public authority at the time of initial construction.

DESIGN SPEED

The design speed of all highways on the system shall be at least 70, 60, and 50 miles per hour for flat, rolling, and mountainous topography, respectively, and depending upon the nature of terrain and development. The design speed in urban areas should be at least 50 miles per hour.

CURVATURE, SUPERELEVATION, AND SIGHT DISTANCE

These elements and allied features, such as transition curves, should be correlated with the design speed in accordance with A Policy on Geometric Design of Rural Highways of the American Association of State Highway Officials, 1965.

GRADIENTS

For design speeds of 70, 60, and 50 miles per hour, gradients generally shall be not steeper than three, four, and five percent, respectively. Gradients two percent steeper may be provided in rugged terrain.

WIDTH AND NUMBER OF LANES

Width of traffic lanes shall be not less than 12 feet.

The number of lanes, four or more, shall be sufficient to accommodate the estimated DHV, and shall be determined on the basis of design capacities for the applicable conditions as given in A Policy on Geometric Design of Rural Highways. On upgrades that exceed the critical design length, analysis should be made for provision of climbing lanes.

MEDIANS

Medians in rural areas in flat and rolling topography shall be at least 36 feet wide. Medians in urban and mountainous areas shall be at least 16 feet wide. Narrower medians may be provided in urban areas of high right-of-way cost, on long and costly bridges, and in rugged mountainous terrain, but no median shall be less than four feet wide.

Curbs or other devices may be used where necessary to prevent traffic from crossing the median.

Where continuous barrier curbs are used on narrow medians, such curbs shall be offset at least one foot from the edge of the through-traffic lane. Where vertical elements more than 12 inches high, other than abutments, piers, or walls, are located in a median, there shall be a lateral clearance of at least three and one-half feet from the edge of through traffic lane to the face of such element.

SHOULDERS

Shoulders usable by all classes of vehicles in all weather shall be provided on the right of traffic. The usable width of shoulder shall be not less than 10 feet. In mountainous terrain involving high cost for additional width, the usable width of shoulder may be less but at least six feet. Usable width of shoulder is measured from edge of through-traffic lane to intersection of shoulder and fill or ditch slope except where such slope is steeper than 4:1 where it is measured to beginning of rounding.

SLOPES

Side slopes should be 4:1 or flatter where feasible and not steeper than 2:1 except in rock excavation or where there are other special conditions.

RIGHT-OF-WAY

Fixed minimum widths of right-of-way are not given because wide widths are desirable, conditions may make narrow width necessary, and right-ofway need not be of constant width. The following minimum widths are given as guides.

In rural areas right-of-way widths should be not less than the following, plus additional widths needed for heavy cuts and fills:

In urban areas right-of-way width shall be not less than that required for the necessary cross section elements, including median, pavements, shoulders, outer separations, ramps, frontage roads, slopes, walls, border areas, and other requisite appurtenances.

CULVERTS

All culverts shall be of sufficient length to accommodate the pavements, median, and shoulders.

BRIDGES AND OTHER STRUCTURES

The following standards apply to Interstate highway bridges, overpasses, and underpasses. Standards for crossroad overpasses and underpasses are to be those for the crossroad.

Bridges and overpasses, preferably of deck construction, should be located to fit the overall alinement and profile of the highway.

On all rural sections the clear height of structures shall be not less than 16 feet over the entire roadway width, including the usable width of shoulders. At urban places the 16-foot clearance shall apply to a single routing. On other urban routes the clear height of structures shall be not less than 14 feet. Allowance should be made for any contemplated resurfacing.

The width of all bridges, including grade separation structures, between inside faces of curbs, when used, or between rails or parapets when curbs are not used, shall equal the full roadway width on the approaches, including usable width of shoulders. Curbs, if used, shall not exceed 18 inches in width. Major long-span bridges may have lesser width which shall be individually analyzed.

On major long-span bridges offsets to face of parapet or rail shall be at least 32 feet measured from the edge of through traffic lane. If used, barrier curbs on such bridges and curbs on approach highways shall be offset at least 2 feet. These dimensions apply on right and left.

The minimum lateral clearance from the edge of through-traffic lanes to the face of walls or abutments and piers at underpasses shall be the usable shoulder width but not less than eight feet on the right and four and one-half feet on the left.

A safety walk shall be provided in tunnels.

PART III BRIDGE LAWS

TITLE 33, UNITED STATES CODE, "NAVIGATION AND NAVIGABLE

Sec. 491.

WATERS"

Chapter 11.-BRIDGES OVER NAVIGABLE WATERS

Approval of and deviation from plans.

492. Bridge as post route; limitation as to charges against Government; telegraph and telephone lines.

493.

494.

Use of railroad bridges by other railroad companies.

Obstruction of navigation; alterations and removals; lights and signals; draws; tolls.

495. Failure to comply with regulations; penalty; removal of bridge.

496.

497.

Time for commencement and completion of bridge.
"Persons" defined.

498. Reservation of right to alter or repeal.

498a. Application of sections 491-497 to bridges authorized prior to June 10, 1930.

498b. Application of sections 491-497 to bridges authorized prior to March 23, 1906.

503. Tolls; reasonableness; bridges to which provisions not applicable. 504. Same; determination of reasonableness by Secretary of the Army; effect of order prescribing toll.

505. Same; review of order.

506. Same; hearings to determine reasonableness; attendance of witnesses; punishment for failure to attend.

507. Same; failure to obey order prescribing toll; punishment.

514. Submission and approval of general plans and specifications. 515. Contracts for project; guaranty of cost.

Noncompliance with orders; penalties; removal of bridge.

518.

519.

520.

Review of findings and orders.

525. Construction and operation of bridges; consent of Congress; approval of plans; private highway toll bridges. Amount of tolls.

526.

527. Acquisition of interstate bridges by public agencies; amount of damages. 528. Statement of construction costs of privately owned interstate bridges; investigation of costs; conclusiveness of findings; review.

529. Sinking funds; rate of tolls, cancellation of tolls.

530. Bridges included and excluded.

531.

International bridges.

532. Eminent domain.

533. Penalties.

*

BRIDGES OVER NAVIGABLE WATERS

GENERAL BRIDGE ACT OF 1906

33 U.S.C., secs. 491-498*

§ 491. Approval of and deviation from plans.

When, after March 23, 1906, authority is granted by Congress to any persons to construct and maintain a bridge across or over any of the navigable waters of the United States, such bridge shall not be built or commenced until the plans and specifications for its construction, together with such drawings of the proposed construction and such map of the proposed location as may be required for a full understanding of the subject, have been submitted to the Secretary of the Army and Chief of Engineers for their approval, nor until they shall have approved such plans and specifications and the location of such bridge and accessory works; and when the plans for any bridge to be constructed under the provisions of sections 491-498 of this title, have been approved by the Chief of Engineers and by the Secretary of the Army it shall not be lawful to deviate from such plans, either before or after completion of the structure, unless the modification of such plans has previously been submitted to and received the approval of the Chief of Engineers and of the Secretary of the Army. (Mar. 23, 1906, ch. 1130, § 1, 34 Stat. 84.)

§ 492. Bridge as post route; limitation as to charges against Government; telegraph and telephone lines.

Any bridge built in accordance with the provisions of sections 491-498 of this title, shall be a lawful structure and shall be recognized and known as a post route, upon which no higher charge shall be made for the transmission over the same of the mails, the troops, and the munitions of war of the United States than the rate per mile paid for the transportation over any railroad, street railway, or public highway leading to said bridge; and the United States shall have the right to construct, maintain, and repair, without any charge therefor, telegraph and telephone lines across and upon said bridge and its approaches; and equal privileges in the use of said bridge and its approaches shall be granted to all telegraph and telephone companies. (Mar. 23, 1906, ch. 1130, § 2, 34 Stat. 85.)

§ 493. Use of railroad bridges by other railroad companies.

All railroad companies desiring the use of any railroad bridge built in accordance with the provisions of sections 491-498 of this title, shall be entitled to equal rights and privileges relative to the passage of railway trains or cars over the same and over the approaches thereto upon payment of a reasonable compensation for such use; and in case of any disagreement between the parties in regard to the terms of such use or the sums to be paid all matters at issue shall be determined by the Secretary of the Army upon hearing the allegations and proofs submitted to him. (Mar. 23, 1906, ch. 1130, § 3, 34 Stat. 85.)

§ 494. Obstruction of navigation; alterations and removals; lights and signals; draws; tolls.

No bridge erected or maintained under the provisions of sections 491-498 of this title, shall at any time unreasonably obstruct the free navigation of the waters over which it is constructed, and if any bridge erected in accordance with the provisions of said sections, shall, in the opinion of the Secretary of the Army, at any time unreasonably obstruct such navigation, either on account of insufficient height, width of span, or otherwise, or if there be difficulty in passing the draw opening or the drawspan of such bridge by rafts, steamboats, or other water craft, it shall be the duty of the Secretary of the Army, after giving the parties interested reasonable opportunity to be heard, to notify the persons owning or controlling such bridge to so alter the same as to render navigation through or under it reasonably free, easy, and unobstructed, stating in such notice the changes required to be made, and prescribing in each case a reasonable time in which to make such changes, and

*49 U.S.C., 1655 (g) (6) (B) transferred the functions of these sections to the Secretary of Transportation.