Page:Toll Roads and Free Roads.pdf/70

50 BRIDGES AND OTHER STRUCTURES

Culverts, bridges over streams, railroad and highway separation structures, and all other structures such as retaining walls would be constructed so that vehicles will have adequate clearance and drivers will feel no sense of restriction at any point.

Structures carrying the traffic of the proposed roads would be designed in all respects except their clearances, in accordance with the Standard Specifications for Highway Bridges of the American Association of State Highway Officials. The live loading would be H-20. Structures carrying intersecting roads would be designed in accordance with the standard practice of the agency in control of the intersecting road but in no case for a live loading less than H-15.

The vertical clearance provided at undercrossings would be at least 14 feet within the limits of the pavement; and horizontal clearances would be such that the shoulders would be carried through the structure opening without reduction in width. Medial parkway strips would not be narrowed and one pier only would be permitted in the middle of them. Future sidewalks, if required, would be carried through in the shoulder area.

When the proposed roads are carried on structures of moderate length (up to about 100 feet) the width of the medial strip would not be reduced and the normal shoulder area would be used for sidewalks. For bridges over 100 feet long the medial strip might be narrowed but in no case to less than 6 feet between curbs. All curbs on bridges would be 2 feet outside the normal edge of the pavement so that the minimum medial distance between normal inside edges of pavements on divided roads would be at least 10 feet. Changes in width of medial strip would be accomplished by gradual transition to avoid all sense of forced alinement.

Substantial bridge railings would be located at the pavement curbs. Sidewalks would be located between the curb and pedestrian railings at the sides of the bridge.

Where it is necessary to omit shoulders, as at high retaining walls, barrier curbs would be placed 2 feet outside the normal edge of pavement and the nearest face of the retaining wall would be at least 2 feet from the face of the curb.

Guardrails, where required, would be placed clear of the normal shoulder and carried continuously past all culverts. The width of embankment would be increased to accommodate the rail. Railings would be extended well beyond the ends of fills to overlap adjacent cuts or shallow sloping fills.

ACCESS POINTS AND TOLL FACILITIES

Access points would not be spaced at regular intervals but would be located to give the maximum service commensurate with the cost of maintaining toll booths and toll operators. For example, the average distance between the access points proposed in New Jersey is 2.6 miles, the minimum 0.5 mile, and the maximum 7.5 miles. In Montana, the average distance between proposed access points is 79.4 miles, the minimum 9.2 miles, and the maximum 140 miles. A typical grade separation, access roads, and toll booths for a fourlane toll road are shown in plate 31. Traffic would always enter and leave the toll road on the right. Liberal deceleration and acceleration