Embedded Turnouts for the Hiawatha LRT Project. Author: David F. Peterson, PE. Parsons Corporation

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1 Embedded Turnouts for the Hiawatha LRT Project Author: David F. Peterson, PE Parsons Corporation Design Manager, Hiawatha Light Rail Transit Project September 30, 2003

2 ABSTRACT Installation and maintenance of turnouts in paved areas have always been something to avoid for both railroads and transit agencies. For the development of the Hiawatha Light Rail Transit Project, a key element is at-grade rail access to downtown Minneapolis. The present north end in downtown requires crossovers in Fifth Street and Nicollet Mall, a confined area congested with utilities and vehicular traffic. Embedded turnouts turnouts installed in paving are required in this and other locations along the Hiawatha corridor. Minnesota Transit Constructors (MnTC), the design-build contractor for the Hiawatha Project Office, elected to use #6 flexive double tongue switches for paved areas. This European Edgar Allen switch design differs from AREMA standard double tongue turnouts by having a flexible switch point set in a fixed casting, a transit type design also being used in Tampa s new LRT system. For containment of stray electrical current to prevent corrosion of nearby infrastructure, the embedded track is electrically isolated. The turnout is constructed in a concrete tub comprised of concrete and insulating membrane and sealed with elastomeric grout. The turnout and tub are constructed with

3 three concrete pours, with the insulating membrane installed between the first and second pours. In most cases, the turnouts are power operated with switch machines between the switch point castings, and heated with calrod-type electrical resistance heaters. The turnouts were fabricated by Progress Rail Services and will be installed by MnTC s subcontractor Railworks Track Systems in early to mid 2003.

4 1. INTRODUCTION Construction and operation of turnouts in paved areas have always been a lessthan-desired alternative to ballasted designs. These embedded turnouts require closer construction tolerances and higher maintenance and are avoided when possible. The Hiawatha Light Rail Transit project in Minneapolis and Bloomington, Minnesota is currently under construction. Hiawatha is a new system linking downtown Minneapolis with the Minneapolis St. Paul International Airport and the Mall of America in Bloomington. The line is approximately 12 miles in length and includes seventeen stations located in commercial and residential areas. Low floor Bombardier light rail vehicles will operate at up to 55 mph at 7 ½ minute headways at peak travel periods. The system requires six embedded crossovers, primarily at the end points of the system to cross trains over for return movements. The design-build contractor, Minnesota Transit Constructors (MnTC), worked closely with the representatives of the Hiawatha Project Office (HPO) to identify

5 the most appropriate embedded track and turnout system for the Hiawatha LRT system. 2. TURNOUT EVALUATION The HPO s two agencies the Minnesota Department of Transportation and Metro Transit, decided during the design development process to use tee rail in lieu of girder rail for embedded track applications. This in turn led to discussions of alternative types of turnouts. AREMA s Portfolio has two embedded turnout types that in the past have been used both for railroad and light rail transit applications. (See Portfolio Plan No and other referenced plans). These turnouts, using tongue and mate and double tongue switches, would have performed satisfactorily. However, these turnout designs are traditionally intended for railroad use, and considering the lower axle loads of Light Rail Transit (LRT) applications, other options were considered. During the evaluation of turnout options during design development, the HPO and MnTC considered the embedded switches manufactured by Edgar Allen Limited in the United Kingdom. Edgar Allen s switches are currently in use by Tampa, Florida s Hartline system and are being installed in New Orleans streetcar system. They are also in use in Sheffield and Manchester, England

6 and Hong Kong. These flexive tongue designs are ideal for paved track applications and can provide maintenance advantages. Flexive tongue turnouts involve a solid manganese steel body with a flexible manganese tongue, acting as the switch point, fastened to the body by two screws. The tongue is easily removed for maintenance or replacement without removing the entire unit. Electrical resistance heaters (calrods) can be placed along the sides or underneath the manganese castings. 3. METALLURGY Edgar Allen s flexive tongue turnouts were introduced in 1992 for the Sheffield Supertram system in the UK. The Supertram system opened in 1995, and Edgar Allen supplied turnout points and castings for six 25m and three 100m radius turnouts. Both the manganese points and bodies are rated at a Brinell Hardness of approximately 250 at manufacture Edgar Allen reports that in the five years after opening of the Supertram system the bodies and points have work hardened to approximately 400 BHN. The castings and points are manufactured using austenitic manganese steel. 4. TURNOUT DESIGN CONSIDERATIONS

7 The Hiawatha designers evaluated other aspects of the turnout design that would ultimately impact the performance of the turnouts. These factors should be considered for any transit project that requires turnouts in paved areas. a. Paving Depending upon whether vehicles will actually drive upon the turnout, careful consideration should be taken regarding the type of paving to be used around the rails and other turnout components. For Hiawatha, it was decided to use portland cement concrete islands between the rails, with asphalt cement concrete infill to approximately six inches from the rail head. This would give better support to the traffic that could potentially cross the turnout and was considered more aesthetically attractive. Based upon discussions with other transit properties, it was decided that using portland cement concrete against the rail would not perform well due to movement of the rail against the concrete, potentially breaking the concrete. It could also present problems with replacement of rail and turnout components and might not provide satisfactory rail to rail insulating properties. b. Electrical Isolation The embedded track for the Hiawatha system was insulated from the ground to protect adjacent utilities and structures from electrical corrosion by using the

8 rubber boot system manufactured by the Iron Horse Corporation cast in portland cement concrete. The turnouts, however, could not use the boot system due to the irregular size and shape of frogs, switch castings, and plates. As a result, the embedded turnouts were constructed in insulated concrete tubs, which are comprised of reinforced concrete with a rubberized isolation liner with protection board. The rails as they enter the tubs are themselves isolated with bulkheads perpendicular to the track. The turnout materials, including rail, plates, frogs, switch machines, switch castings, and the concrete islands discussed above are installed in the tub. Rail and switch components are mounted on elastomeric grout pads that provide additional insulation and shock resistance. c. Switch Machines The Hiawatha LRT system, as currently designed, has six crossovers in embedded track. Four crossovers are powered using Hanning & Kahl (H&K) switch machines, and the other two crossovers use hand throw turnouts. Spring switches, although common on other systems, were not utilized for operational reasons. The power switches are powered by H&K Model HW(E)61V. The switch machines are located between the switch casting and each switch machine box is drained with non-conducting PVC pipe to the storm drainage system. Power and signal conduit to the switch machine and turnouts run through the isolation

9 membrane and are insulated. Both bonded and poly bar insulated joints are used and are identical to those in standard track applications. Hand throw switch boxes are also located between the switch castings. d. Switch Heaters Since Minnesota winters are long and cold with plenty of snow, the embedded turnouts will be heated using electrical resistance heaters (calrods). There was considerable discussion within the design team regarding whether to install the heaters along the side of the switch castings or underneath. There is no ideal way to heat the switches, since the heaters will be in contact with other materials such as asphaltic concrete or elastomeric grout. Discussions with other transit properties revealed that both methods of heating are used. The Hiawatha designers decided to place two heater rods in metal conduits under each casting, above the concrete and far enough away from the elastomeric grout pads to avoid overheating of the pads. The heater rods can be pulled out of the conduit and replaced without removing the switch casting or conduit. By installing the heater rods underneath, it avoids the inevitable melting of asphalt concrete along the side of the casting, and the dual heater rods provide redundancy. e. Drainage

10 The paved areas in downtown Minneapolis and suburban Bloomington are generally flat and drainage is a challenge. In warm climates, poor drainage in embedded turnouts can be a nuisance in Minnesota, with long periods of subfreezing weather, frozen switch mechanisms could put a turnout out of service for months. The embedded turnout tubs and embedded trackbed are provided surface drainage and the switch machine boxes are also drained. Switch heater rods will be placed in the switch drains to keep them clear during the winter season. 5. CONSTRUCTION METHODS At the time of this writing, the embedded turnouts for the Hiawatha LRT project are under construction. The construction of the turnouts is very time consuming compared to construction of ballasted turnouts and takes several months from start to finish. The construction of the turnouts can be discussed in terms of the three concrete pours, as follows: a. First Pour The Isolation Tub The reinforced concrete isolation tub is constructed on select base material, with conduits in place for drainage and systems (traction power and signal) facilities. The first concrete pour is eight inches thick, with walls up to top of rail longitudinally on the field side of the rails, and with the concrete bulkheads to top of rail between the rails at the ends of the tubs.

11 After placement of the concrete, the isolation liner is placed on the bottom and sides of the tub. The rubberized liner is heat welded and the welds electrically tested. The liner is installed with one-eighth inch thick protection board on both sides of the liner. The following exhibits show the details of the turnout design. The three stages of construction, labeled First Pour, Second Pour, and Final Pour are included. The concrete pour for that phase is cross-hatched in the cross sections. Plan View Isolation Tub for Crossover Hiawatha LRT Design-Build PAVEMENT INFILL TRANSVERSE C OF CROSSING L B CONCRETE 1 MIN C L TRACK NO. 6 TURNOUT WITH DOUBLE TONGUE SWITCH PER SPEC MIN. A SWITCH DRAIN (AT EACH SWITCH) PS C SWITCH AND COVER PLATE FLOW 2-0 MIN. 9º31 38 PITO TUB DRAIN (AT LOW END) CONCRETE 2-0 (MIN.) SWITCH BLOCK OUT C DETAIL A 4-0 MIN. 7 - MAX FLOW POURED POLYMETRIC JOINT SEAL FOR LESS THAN 2 GAP IN RAIL HEAD B CONCRETE PAVEMENT INFILL C L TRACK 38 MAX. A EMBEDDED TRACK SLAB Exhibit I, Plan View, Isolation Tub

12 Hiawatha LRT Design-Build Isolation Tub First Pour PAVEMENT 3-0 MIN. 6 1% 1% #4 REBAR 18 ON CENTER L TRACK ALONG C L TRACK C L TRACK 4 VARIES ½ GAUGE 18 CONCRETE 4-8 ½ GAUGE CONST. IN FILL JOINT LEVEL PCC 2 1/2 CLEAR 3 CLEAR 1% 3-0 MIN. INSET CURB AND GUTTER AND SIDEWALK 1 4 x 4 CHAMPHER 2 ISOLATION MEMBRANE PROTECTION 2 BOARD 3 ISOLATION TUB 1 AGGREGATE BASE, CLASS 5 (02211) NON-FROST SUSCEPTIBLE SOIL ELASTOMER GROUT Exhibit II, Isolation Tub, First Pour Hiawatha LRT Design-Build Section D-D End of Isolation Slab TUB EMBEDDED TRACK SLAB SPECIAL TRACKWORK PLATE WITH E.G. PAD 1 115RE RAIL #5 BETWEEN RAILS BEND UP #6 BAR HORIZ. REINF. 4 x 4 ISOLATION SLAB CHAMFER TOP OF RAIL 2 ELASTOMER GROUT SEAL FOR MEMBRANE EDGE 1 EXPANSION JOINT MATERIAL AND SEALER #6 BETWEEN RAILS TUB REINFORCEMENT PROTECTION BOARD #6 TOTAL 3 EPOXY COATED # ISOLATION MEMBRANE TUB (WORKING SLAB) 9 Exhibit III, End of Isolation Slab b. Second Pour Support for the Rail

13 A strongback system and jacks are used to support the assembled turnout in the proper line and grade prior to the second concrete pour. Anchor bolts and inserts for the turnout plates are placed in the plates in position for embedment in the concrete. Plastic caps are placed over each of the e-clips to prevent fouling during the concrete pour and for protection afterward when asphalt is placed against the rail. Hiawatha LRT Design-Build Isolation Tub Second Pour PAVEMENT 3-0 MIN. 6 1% 1% #4 REBAR 18 ON CENTER L TRACK ALONG C L TRACK C L TRACK 4 VARIES ½ GAUGE 18 CONCRETE 4-8 ½ GAUGE CONST. IN FILL JOINT LEVEL PCC 2 1/2 CLEAR 3 CLEAR 1% 3-0 MIN. INSET CURB AND GUTTER AND SIDEWALK 1 4 x 4 CHAMPHER 2 ISOLATION MEMBRANE PROTECTION 2 BOARD 3 ISOLATION TUB 1 AGGREGATE BASE, CLASS 5 (02211) NON-FROST SUSCEPTIBLE SOIL ELASTOMER GROUT Exhibit IV, Isolation Tub, Second Pour The concrete is placed within the tub to a level one inch below the turnout plates. The one inch vertical gap will be filled with elastomeric grout, which provides electrical isolation and support for the plates, after the second pour concrete is

14 cured. The reinforcement in the second pour is of course separate of the reinforcement in the first pour due to the design of the isolation liner, but hoops of rebar are included in second pour to secure the islands above, which are part of the third pour. c. Third Pour Concrete Islands While elastomeric grout is being poured under the turnout plates, systems work can be done, including bond wires to rails for power feeds and signals, setting and adjusting the switch machines, and installing and testing the insulated joints. The third and last concrete pour brings the concrete between the rails and on the field side of the rail against the isolation liner to top of rail. Hiawatha LRT Design-Build Isolation Tub Final Pour PAVEMENT 3-0 MIN. 6 1% 1% #4 REBAR 18 ON CENTER L TRACK ALONG C L TRACK C L TRACK 4 VARIES ½ GAUGE 18 CONCRETE 4-8 ½ GAUGE CONST. IN FILL JOINT LEVEL PCC 2 1/2 CLEAR 3 CLEAR 1% 3-0 MIN. INSET CURB AND GUTTER AND SIDEWALK 1 4 x 4 CHAMPHER 2 ISOLATION MEMBRANE PROTECTION 2 BOARD 3 ISOLATION TUB 1 AGGREGATE BASE, CLASS 5 (02211) NON-FROST SUSCEPTIBLE SOIL ELASTOMER GROUT Exhibit VI, Isolation Tub, Final Pour

15 The approximately six inch gap between the ball of the rail and the island concrete will be filled in later to top of rail, along with a flangeway, with an asphalt concrete infill to finish the work. 6. SUMMARY The embedded turnouts for the Hiawatha project will be operated in a harsh weather environment and will be critical to the successful operation of the system. The Edgar Allen turnouts, while fairly new to North American transit systems, have been proven to be reliable in Europe and its design should perform well in street conditions in Minneapolis and Bloomington.