Modifying Freeway Geometrics to Increase Capacity

Every sector of urban transportation faces the problem of rising costs, limited funds, and depleting resources with which to provide for increasing travel demands. One approach to the solution is restriping the mainline pavement with narrower lane widths and encroaching on the shoulders to create an additional lane for travel. This technique has been applied successfully on local and arterial streets. However, only in the last 10 yrs have transportation departments considered similar changes to cross sections of urban freeways. This paper presents a state-of-the-practice as developed from a survey of the states. The designs for six general types of modifications are examined and specific results from 14 operational projects are summarized. The general consensus of the study is that surface modifications are cost effective techniques for increasing freeway capacity. The modified freeways have improved safety records because of the increase in capacity, but accident severity may increase with time as traffic demands increase.