STREET PLAN. Since an engineer is occasionally called upon to plan a city, and often to lay out additions to cities and vil lages, the various street plans for the city will be considered. In plan ning the streets of a city three objects should be kept in mind ; viz.: (1) the subdivision of the area in such a manner as to give the maximum efficiency for business or residence purposes; (2) sufficient accommodation for the pedestrian and vehicular travel on the streets; and (3) good drainage and easy communication between the different parts of the city.
Lots are seldom less than 100, nor more than 180, feet deep; and usually vary from 100 to 150 feet. A lot more than 150 feet deep is objectionable, because of the temptation to build unsightly residences fronting on the alley and because of the difficulty of keeping a deep lot in good sanitary condition.
For convenience, especially in business districts, it is best to have an alley run lengthwise through the block. The alley varies from 10 to 30 feet, but is usually from 16 to 20 feet.
The above depth of lot and width of alley makes the width of the block 2'20 to 330 feet. The length of the block will depend
upon the requirements for traffic perpendicular to the principal streets. Sizes of blocks vary much in any particular city, and Ptill more between different cities. The following are the dimen sions of typical blocks in several cities: Boston, 220X 400 ft., and 100 X MO ft.; New York, 200 X 900 ft., and 200 X 400 ft.; Phila delphia, 400 X 500 ft., and 500 X 800 ft.; Washington, 400 X 600 ft., and 300 X 800 ft.; Montreal, 250 X 750 ft.; Chicago, 300 X 350 ft., and 300 X 500 ft.
Fig. 81 is given to illustrate the advantages to be derived from a careful study of the best size of blocks and of the most advan tageous arrangement of streets. The left-hand side of the dia gram shows the typical arrangement of streets and blocks in the residence district of New York City, the shaded portions repre senting the usual buildings. The right-hand side shows a much superior arrangement.* The three center blocks of the present plan comprise an area of 720 X 800 feet, and contain 480,000 sq. ft. of building area and 96,000 sq. ft. of streets; and in the corre sponding area of the proposed plan, there are 481,000 sq. ft. of building area and 94.200 sq. ft. of streets; therefore the two plans give substantially the same area for buildings and for streets. In the first case the length of streets is 1,600 feet, in the second 1,520 feet; therefore the two plans have practically equal light and air. The proposed arrangement is the better in the following partic ulars: 1, number of corner sites; 2, accessibility of rear entrances for delivery of provisions, coal, etc., and the removal of garbage, ashes, etc., and in case of fire; 3, removal from the street of dangerous and cramped cellar entrances; 4, removal from the main or primary streets of the loading and unloading of trucks; and 5, increased transportation facilities in a direction perpendic ular to the length of the original blocks.