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Rh A less satisfactory solution, as shown by the examples in plate IX, can be achieved by taking the tier of properties on one side of an existing street, retaining that street as one of the essential local service ways and constructing another at the opposite side of the depressed route. This will usually result in a somewhat cramped development and will expose to the express route the rear of properties at one side.

It will generally be preferable, however, to the third alternative, which is to take properties on both sides of an existing street. The latter would prevent salvage of the existing street and require the construction of two new service ways, to both of which the rear of abutting properties will be exposed.

In the outer and residential sections of large cities and in small cities generally, neither the elevation nor the continuous depression of express routes is recommended. In such sections a more appropriate design, developed on a block-wide right-of-way, may utilize the existing surface streets at the two ends of the acquired block without change as local service ways. The ample intervening space may be used for a parklike development of the express way, which would be constructed on long, rolling grades to pass under bridges built at the street level of crossing and access streets and intervening pedestrian bridges, as pictured in plate X.

Except in the largest cities, it will probably not be necessary to extend express routes through the central business section. In the first place, it may usually be assumed that substantially all of the traffic approaching the business section of a city is destined to that area, and will be discharged at its fringe, there to enter the central street system or a parking garage. In the second place, city-penetrating express routes, where they extend continuously across a city, can generally be located tangentially to the central business area. If and when it is necessary to extend an express route through a central business area, elevated or tunneled locations will usually be the more appropriate choices.

As indicated by the foregoing discussion, provision of the physical installations essential for limitation of access, though costly, involves few problems that have not been encountered in the design of ordinary main highways. The greater right-of-way requirements present more serious difficulties; and the present lack of specific legal sanction for the establishment of limited-access highways is a positive obstacle in many States.

The courts have recognized that abutting property owners have certain rights in existing streets and highways. These rights include the right of ingress to and egress from their property, and in some cases the right of visibility as well as the right to the flow of light and air from the street to the property. Moreover, it is well established in the common law that the right of access cannot be denied or restricted nor can an owner be deprived of such right except upon the payment of just compensation and in a manner not inconsistent with due process of law, and for a public use or purpose.