40 TRANSPORTATION RESEARCH RECORD 1299 Movable Concrete Barrier Approach to the Design and Operation of a Contraflow HOV Lane CHRISTOPHER M. PoE A 5-mi-long contraOow lane is being cons1ructcd on - a t R.L. movable barrier to separate construction zone activities from Thornton Freeway {lH-. 0) in Dall a , Texas. T his i a joint project traffic, some requiring daily operation. of the Texas Highway D epartment and Dallns Area Rapid Tran­ During the past year, Tri has been reviewing the detailed sit. The lane will provide hi gh- occupancy vehicle (HOV) a travel design of the contraflow lane, in developing the performance time savings of up to 10 min compared with traffic opernting in th e conge ted mainlanes. Thi:; pri rity rreatm ent project i uniqu specification for the movable barrier system, and in devel­ because it uses a movable concrete barrier system in rhe design oping the operations plan and operating manual for the con­ and operation of the contranow lane. The movable barrier sys­ traflow lane. The purpose of this paper is to explain some of tem, which con i. ts of a barrier transfer vehicle and a continu ou the design and operational issues that must be considered in concrete barrier, will provid "' greater safety by physically cpa­ designing an HOV facility that uses a movable barrier system. ra ting HOV. from the oppo ing troffic in the general-purpose This paper also discusses advantages and disadvantages of a lanes. Although comraflow lanes have trnditiom11ly been re- trict d to bu cs and authorized vanpool fo r safety rea ·ons, th i movable barrier system when applied in the design and op­ relatively new technology will permit carpools lO safely use the eration of a contraflow lane. lane as well . The decision to use the movable I arrier y tern in tead of pylons to designate the priority lane essentially doubled the capital and opernring costs of the pr jeci; however, the car­ DESCRIPTION OF IH-30 CORRIDOR pool demand 11 lso doubled th e number of passenger-hours of travel time saved. The gremer afety. attrncti n of carpools, greater East R .L. Thornton Freeway is a major 8-lane radial freeway perception f utilizarion, and ability l move more people in th e peak period made the ba1Ticr ysrem an anrnctive demonstration located on the east side of Dallas (Figure 1). The freeway project. This paper discu. es de ign and operational issues as­ primarily serves commuters destined for the central business sociated with usin g the movable barrier system for u contranow district or employment centers to the north and west of the 1lOV I ne. Elt: 1111:11ls requiring special attention were the , ccess district. The presence of significant volumes of commuting location design, barrier end rreatment, equipment storage and traffic results in a high directional split during the peak pe­ maintenance, set-up and take-down techniques, and enforcemcm procedure .. riods. Approximately 70 percent of peak-hour traffic is trav­ eling in the peak direction. East R.L. Thornton Freeway experiences recurring conges­ The Texas State Department of Highways and Public Trans­ tion during both peak periods. In the morning, average vehicle portation (SDHPT) and Dallas Area Rapid Transit (DART) speeds are less than 30 mph for more than 1 hr in a section identified four freeway corridors in the Dallas area to be that extends for 5 mi. In the evening, average vehicle speeds evaluated for determining the short-term feasibility of imple­ are less than 30 mph for more than an 1.5 hr in a section that menting high-occupancy vehicle (HOV) lane projects. extends for a little more than 3 mi . The Texas Transportation Institute (Tri) researched the There are geometric design features in this corridor that feasibility of HOV alternatives in these corridors. The most present constraints in designing short-term improvements. Near favorable project was determined to be a contraflow lane on the downtown there is an elevated freeway section approxi­ East R .L. Thornton Freeway (IH-30) that used a movable mately 1 mi long, and the eastbound and westbound mainlanes concrete barrier to separate the HOV traffic from the op­ are on two separate structures at different elevations. Also, posing general-purpose traffic in the off-peak direction (1) . there is a bridge structure over the White Rock Creek that The East R.L. Thornton Freeway contraflow lane is the has no inside shoulder for the half-mile length of the hridge. first demonstration project on HOVs in Dallas undertaken by DART and SDHPT. This project will also demonstrate the use of a movable barrier system in an HOV application. ALTERNATIVE SELECTION The movable concrete barrier has not yet been used in a permanent application in the United States; however, there The Texas SDHPT has plans to build additional mixed-flow have been several construction projects that have used the capacity in the IH-30 corridor by 1995. DART and SDHPT were interested in short-term improvements that would in­ crease the capacity of the freeway for buses and carpools. Transportation Institute, Texas A & M University System, 1600 East The possible alternatives for the HOV facility were iden­ Lamar Blvd., Suite 120, Arlington, Tex. 76011. tified as follows: (a) an exclusive HOV facility in the median; Poe 41 EAST R.L. THORNTON FRWY Ill I"' I SAMUELL I II) I C'I') ~ ~ ~ IO l£l ~ = = a ~ / 8 ; ~ i !§... ! 12 \ = = FIGURE 1 Study corridor. (b) a concurrent-flow HOV facility on the inside shoulder; or does not exist. Furthermore, a concurrent flow lane without (c) a contraflow HOV facility using a lane in the off-peak a shoulder does not allow adequate enforcement. Considering direction. The intent of the intermediate facility was to pro­ experience in other cities, many vehicles use an HOV lane vide a cost-effective improvement that could be operating in illegally if enforcement is not visible, effective, and safe. High 18 to 24 months. violation rates on the first HOV project in this area would The bridge structures at different elevations near downtown be detrimental to future projects. eliminate the short-term feasibility of an at-grade facility in The contraflow HOV lane can be designed and operated the median. An elevated structure would be required over on the inside freeway lane of the off-peak direction. This the bridge sections. These structures could not be designed requires no additional construction over the bridge structures and built in the 18- to 24-month time frame. and only minimal construction at the access-egress points. The The inside shoulder is not continuous, thus making a con­ controlled-access points aid in enforcement by limiting the current flow lane infeasible. Two sections, near IH-45 and number of locations vehicles can enter the lane. Use of the over White Rock Creek, essentially have no inside shoulder. inside lane of the off-peak direction also allows the contraflow A 10-ft inside shoulder exists for the remainder of the freeway lane to have a shoulder for incidents and enforcement. corridor, but long sections of the shoulder have significant A primary constraint with contraflow operation is the traffic cross slopes that require extensive retaining walls. Even with volume in the off-peak direction. Operation of the contraflow considerable reconstruction and narrowing of the general­ lane can only continue as long as general-purpose lane traffic purpose lanes, a desirable buffer zone between the concurrent volumes in the off-peak direction are low enough to operate flow HOV facility and the congested general-purpose lanes with one less lane available for general-purpose traffic. East 42 TRANSPOR TA TION RESEARCH RECOR D 1299 R.L. Thornton Freeway has relatively low traffic volumes in are other benefits realized from this type of project; however, the off-peak direction. A more detailed discussion of the es­ not all are easily quantified. timated life of the project is presented subsequently. The cost of building a contraflow lane with pylon separation (no movable barrier) included construction at the access points, HIGH-OCCUPANCY VEHICLE DEMAND restriping the freeway, signing, support vehicles to place py­ lons, and operating costs. The annualized cost was estimated Peak-period traffic counts were conducted to determine the to be $1.3 million per year (capital costs were amortized over existing hus volumes, carpool volumes, and occupancy rates. the four year life of the project and :uicled to the annual There are approximately 70 DART buses in the peak hour operating costs). This resulted in a benefit-cost ratio of 1.5. within the corridor, all having destinations in the downtown This pylon-separated contraflow lane would be limited to buses area. The peak-hour person volumes in buses are slightly over and vanpools only for safety reasons. 2,500 persons. There are also approximately 800 total carpools However, if a movable barrier system were to be imple­ in the peak hour on the freeway; 660 are two-occupant car­ mented, carpools could also operate in the contraflow lane. pools and 130 are three-or-more occupant carpools (vanpools The addition of the movable barrier and the barrier transfer are included in the 3+ occupant carpools). These carpools vehicles increases the annualized cost of the contraflow lane carry an estimated 1,800 persons in the peak hour. to $1.9 million per year. (It was assumed that the barrier The bus volume in this corridor is one of the largest in the system will have a residual value equal to 30 percent of the Dallas area. However, almost half of the potential HOV mar­ initial cost after 4 years of operation.) Including 2 + occupant ket is carpools.