COPYRIGHT, 1909, BY COMMERCIAL CLUB OF CHICAGO ] The thoroughfares of a city may be divided into three classes: the street, by which is meant the general type of artery; the avenue, on which tides of traffic and travel surge back and forth; and the boulevard, designed primarily as a combination of park and driveway. The first consideration for all thoroughfares is cleanliness, which is the result of a good roadbed kept in thorough repair, and unremitting care on the part of the city cleaning department. In the congested retail district the desirable street width is from 80 to 100 feet, about equally divided between sidewalks and roadway. Here the pavement should be smooth and noiseless; there should be frequent islands of safety for the pedestrian crossing from side to side, and occasional subway crossings; and the lighting, the signs, and every accessory of the street should be arranged with regard to the dictates of good taste. For streets carrying heavy tonnage a width of from 70 to 90 feet is desirable, with a roadway width of a little more than one-half the entire space, and here the pavements should be of the most enduring character, regardless of noise.[22] [Illustration: XC. CHICAGO. THEORETICAL DIAGRAM OF STREET CIRCULATION, SHOWING EXISTING LINES OF TRAVEL (BLACK), AND PROPOSED SUPPLEMENTARY LINES (ORANGE). Circulation from north to south and east to west is already established by the rectilinear system of streets. There is need of additional facilities to be provided by street widenings and new arteries. Circulation towards the center is partially established, but the arteries need extending and developing, and circulation across the city from the northwest to the south and east and from the southwest to the north is lacking. It is proposed to remedy this lack by extending existing diagonal streets. COPYRIGHT, 1909, BY COMMERCIAL CLUB OF CHICAGO ] On residence streets the area devoted to pavement may well be lessened to from 20 to 36 feet, according to the amount of traffic, in order that greater area may be obtained for trees and grass plots. This is highly desirable where, as in some sections is inevitable, houses are crowded together or apartment buildings abound, so that the smaller children may have playgrounds close at hand, and restful shade may prevail. A well-kept grass plot in front of the house induces habits of neatness and comfort within; and cool shade brings people from cellars and dark rooms out into the light, thus contributing to good order and a higher morality.