Evaluation of HOV and Shoulder lane Travel Strategy for I-95 BY CHUNG

Interstate 95 (I-95) is the major northsouth traffic artery for much of’ the eastern United States. In the Washington, D. C., area 1-95 joins I-495 (the Capital Beltway) to carry an extraordinary volume of the region’s traffic. In Northern Virginia, I-95 runs through Fairfax County, where it figures heavily in morning and afternoon commuting for thousands of motorists. The cumulative demand far exceeds roadway capacity: Traffic has been operating at extremely congested and unacceptable service levels during the peak hours for many years. Capacity bottlenecks at on-ramps and off-ramps and weaving areas, and some construction locations have resulted in traffic queues extending for several miles. Long delays are experienced consequently on both the freeway and on adjacent arterials. The significant increases in freeway traffic volumes, site developments within the area, and rightof-way restrictions have made traffic management of the corridor a major challenge for the Virginia Department of Transportation (VDOT). Twenty-four hour shoulder lane travel was adopted in December 1991 in conjunction with the existing HOV-3 lane operation as an interim strategy to relieve the congestion until construction activities are completed.’ These actions have created a new category of freeway operation in the United States. Public concern about the effectiveness of the strategy and the potential safety effects prompted VDOT to undertake a system analysis of the corridor’s traffic operations. This study focuses on an approxi mately 7.7-mile section from U.S. Route 1 North of Woodbridge to Franconia Road (Route 644). The study section is an eight-lane (including shoulder travel lanes) divided freeway. In each direction, the left lane is designated for HOV-3 vehicles during peak hours; the remaining two lanes and right shoulder lane are used as conventional lanes. Four interchanges are included in the corridor: I-95 at U.S. Route 1 (Jefferson Davis Highway), at Route 642 (Lorton Road), at Route 617 (Fairfax County Parkway), and at Route 644 (Franconia Road). All interchanges are combination type with partial cloverleaf and diamond configurations. Travel lanes are generalIy less than 12 feet (ft) wide. Before implementing the strategy, shoulder lanes were reinforced to handle the traffic load, and emergency pull-off locations were designated with pavement markings and signs. Each pull-off area is paved and is 300 ft long and 12 ft wide. There are 200 ft of transition to and from each site. The spacing between pull-off areas is approximately one-half mile. In 1991 the annual average daily traffic (AADT) was 156,400 on the corridor, a 12 percent increase over 1990. Directional splits are approximately equal. Traffic distribution per lane varied by time and location; the maximum reached 31 percent of total directional volume. Land development along the freeway is of mixed-use type, including commercial, industrial and residential. The highly developed land use, continuing roadway construction, and HOV/shoulder lane travel strategy ha$~ created a very complicated traffic operation pattern on the corridor. HOV has been a part of the transportation system on some U.S. freeways since the 1970s, and since its implementation more than 20 cities have developed HOV facilities. The costeffectiveness of HOV facilities has been evaluated in various studies.z However, information about the study of combined HOV/shoulder lane travel strategy has not been found. The purpose of this study was to evaluate the impact of the HOV/shoulder lane travel strategy on traffic operations and safety, to identify actual and potential problems, and to suggest measures for remediation.