four feet in the clear between curbs will take care nicely of four lines of automobiles, and the middle twenty feet thereof may carry a double track for an electric railway.

From the viewpoints of both economy and public convenience it is better to pass at once from a two-line-travel deck to a four-line-travel deck, because a width great enough for only three lines is unsatisfactory in that, as before indicated, it offers to reckless drivers a fine opportunity for head-on collision and, again, it is not as suitable for high speed as a wider structure. It is true that in the case of a total break-down it has a decided advantage over the two-line-travel deck, permitting vehicles to pass around the obstruction, but that is not sufficient reason to warrant its adoption.

Footwalks are often made much wider than necessary, but sometimes too narrow. The minimum width should be five (5) feet, which will just permit two people to walk abreast and to carry umbrellas. Any smaller width would be uncomfortable, and one a foot wider would be better. A width of eight (8) feet is generally sufficient for all requirements, but sometimes ten (10) or even twelve (12) feet are called for. If travel in both directions is permittted on the same footwalk, it should not be made less than seven (7) feet wide, and preferably nine (9) or ten (10), but it is seldom good policy to allow such traffic, because the pedestrian travel will be faster if it is always kept to the right-hand side of the structure.

If a bridge is very long, it is not likely that there will be much pedestrian travel over it, unless there be some special inducement such as beautiful scenery or cool breezes in hot weather, consequently the omission of side-walks, either entirely or temporarily, becomes an economic question of some importance. Sometimes, however, the obtaining of a charter for building the bridge is conditioned upon putting on sidewalks; and in that case the only economy practicable would be to obtain from the authorities permission to provide for their future addition and to omit them temporarily until the development of traffic indicates their necessity. In very long bridges it is economical to reduce the sidewalk width to the absolute minimum of five (5) feet, owing to the small number of people that are likely to pass over the structure on foot.

When a steam-railway bridge has to carry electric-railway cars as well, it is often economic to adopt the expedient of gauntleted tracks, i.e., separate lines of rails for the electric railway lying quite close to the steam-railway rails and with no connection thereto, switches being omitted and the steam-railway rails being cut so as to permit the wheels of the electric-railway cars to cross them on a frog. This expedient obviates the necessity for increasing the railway live loads in order to provide for the electric-railway traffic.

The question of what arrangement of decks to adopt for the accommoda- tion  of  several  kinds  of  traffic  is  an  economic  problem that sometimes arises in a bridge  engineer's  practice.  It  has  lately come up in  the  author's