Four Basic Types Proposed840,000 people in St. Louis owned 165,000 automobiles and trucks in 1946. By 1970 it is estimated that there will be about 230,000 automobiles and trucks. This figure does not include streetcars and busses or the many thousands of new cars and trucks in suburban areas, all of which are potential users of city streets. The annual traffic in St. Louis will be increased from 1,531,000,000 to 2,403,000,000 vehicle miles by 1960 (Estimate by Missouri State Highway Department, Highway Planning Survey.).

…

Since 1916 St. Louis has expended over $40,000,000 in opening, widening, connecting, and extending the system of major streets. Much has been accomplished in converting a horse and buggy street system to automobile needs. As the total volume of traffic increases, however, certain new needs arise…there is a need for complete separation of grade where traffic volume is sufficiently heavy to justify the cost involved. The Federal Government, which has helped finance our splendid system of national highways, has recently revised its policies and Congress has appropriated substantial funds to aid the cities in the construction of express highways and for facilitation of traffic flows from certain selected state highways through metropolitan areas to the central business districts of large cities. Past and present experience reveals the need for four types of major streets and trafficways as follows:

1. Secondary Streets (4 Lanes)
   Most St. Louis streets were laid out with a width of 60 feet. A considerable volume of traffic can be accommodated in a 60-foot street with a 40-foot roadway, especially if curb parking is restricted at times of heavy traffic flow…
2. Major Streets (6 Lanes)
   Their general width of 80 feet permits a 54 or 56 foot roadway to accom modate six lanes of traffic. There is need for quite a number of such routes where traffic volume is insufficient to warrantgreater width of the street except by expensive widening of the street.
3. Major Streets (8 Lanes)
    They are the dominant structural elements of the street plan. Their traffic capacity is unusually high since they permit three or four lanes of moving traffic in each direction. It is impractical to provide for streets with wider roadways because of weaving and complications encountered in traffic control.
4. Express Highways
   When traffic volume becomes so great that it cannot be accommodated even on eight lane surface highways it becomes necessary to provide for uninterrupted traffic flows through grade separations in the form of depressed roadways in wide right-of-ways or by roadway elevation. An overall right-of-way width of 200 feet is generally considered a minimum standard. This is far more costly than street widening but a limited mileage can be justified where there is sufficient traffic volume.

   Express Highways-Interstate
   This is an expressway, which is on the Federal Interstate System to be constructed in part with Federal aid funds, in part with State Highway funds, and with some limited local cost participation.

Plate 18

Plate Number 18

shows the widths of roadways, sidewalks, planting strips and the placement of street lights and street trees for each of the above basic types of major streets and traffic ways. 

plate 19

The new Major Street Plan, Plate Number 19, has a total mileage of 301.7 which is 28 percent of the total 1100 miles of streets in St. Louis. The mileage in each of the five major classification is shown by Table Number IX.
Table Number IX

a) Includes both streets constructed and streets provided for by ordinance to be constructed.

St. Louis has never established building lines on major streets to require new building construction to set back to future street lines. Numerous American cities established such building lines many years ago for purposes of economy and to assure sufficient street capacity to meet future traffic needs. Building lines should now be established on all major streets of inadequate future width.

Because of the extremely heavy traffic between the business district and the western part of the city a new express highway is recommended which would follow approximately the line of Pine, Chestnut and Laclede to Grand Avenue, thence along Forest Park Boulevard to Kingshighway, thence along the west side of the Wabash Railroad through Forest Park to DeBaliviere Avenue and thence along the old Rock Island right-of-way to Skinker Boulevard. This would be a distinctly local expressway.

The Interstate Express Highways on the Federal system are U. S. 40 both east and west from St. Louis, and U. S. 66 both southwest and northeast from St. Louis, and U. S. 50 eastward from St.Louis. Recommended locations for these Interstate Highways have been the subject of much careful study and discussion with State and Federal officials, as well as with local groups. The proposed routes are shown on the Major Street Plan.

Read the rest here: http://stlouis.missouri.org/government/docs/1947plan/streetstra.html