The new Milwaukee Streetcar system has been in the planning, design and construction phases for over 10 years and on November 2, 2018, operations with a combined overhead contact system and streetcar battery power commenced ushering in a new era of growth for the City of Milwaukee. Many challenges in the design and construction of the overhead contact line and power system were encountered during this time period including budgetary constraints, multiple pole location changes, underground obstacles, low clearance bridges, alignment changes, utility conflicts, and changing vehicle requirements. The line was originally designed for pantograph operation but soon adapted for pole/pantograph current collection and then changed back to pantograph only current collection during the final design. The original design consisted of underground feeder cables to supplement a 4/0 contact wire but eventually not utilized due to budgetary constraints. Instead, a larger 350 kcmil contact wire was used with no paralleling feeder cables. The added weight of a 350 kcmil wire with wind, ice and low temperatures created high forces in the overhead contact system (OCS) leading to challenges in pole and foundation design where compliance to the National Electrical Safety Code (NESC) was required. The OCS style originally proposed and finally constructed used an inclined pendulum suspension (IPS) system that was constant tensioned with rotating springs deemed by the installing contractor superior to balance weights. The pendulum system was chosen as it is simple, lightweight, less visually obtrusive, and more economical than other suspension systems such as stitch and steady arm that are being used on other streetcar or light rail systems. IPS has provided Milwaukee with an excellent operating overhead contact system. Buildings along the route that were not historic structures were utilized where possible for span wire attachment but in many locations long bracket arms up to 40 feet long had to be used requiring special designs to keep the size of the pipes standard with the rest of the system. Challenges arose at low bridge underpasses where the contact wire had to be below required code height and special precautions had to be undertaken. Other areas such as the St. Paul Lift Bridge proved challenging as well where special electrically interlocked OCS devices were initially designed to de-energize the overhead wires and is further discussed with the reasoning for their use. This paper outlines the phases of design, the changes to the design that occurred over time, the challenges encountered to the OCS design, the method of design, and the final disposition of the design for construction. It further outlines the construction of the system and problems encountered with poles, foundations, bracket arms, traction power substations, contact wire, feeder cables, and winter conditions affecting the integrity of these structures and how some of these problems were solved.

Overhead Contact Systems for electric transit vehicles utilize catenary or single contact wire suspended from cantilevers, bracket arms or span wires. For single contact wire, inclined pendulum suspension provides optimal performance for pantograph or trolley pole current collectors, though it is under-utilized in the United States. Typical suspension for single contact wire consists of direct suspension hangers or stitch suspension with steady arms where stagger is achieved by pulling off the contact wire with the hanger (direct suspension) or steady arms (stitch suspension). This results in the full weight of the contact wire in the span length being supported by the stitch or line insulator. This rigid point of attachment results in a heavy, stiff suspension leading to current collector bouncing, arcing and premature contact wire wear as the upward movement of the wire is restricted and a hard spot is created. It also results in excessive sag at elevated temperatures and contributes to an increased angle at the support span approach. Inclined pendulums can be utilized in constant tension systems or variable tensioned systems where they impart a semi-constant tensioning into the line and keep the wire tension relatively stable over a particular temperature range. The expansion/contraction of the contact wire is taken up in the inclination of the pendulums where they rise or fall so that the tension and sag in the contact wire remains relatively consistent. In addition, they provide less resistance to uplift of the current collectors at the suspension point so that rising of the contact wire occurs as the collector approaches and passes under it. The vertical angle of the contact wire approaching the span support is kept to minimum levels and collector performance during hot weather conditions tends to remain trouble free. Further, the energy wave set up in the wire from the moving collector is not grossly reflected at the suspension point as with direct suspension thus allowing the collector to pass through smoothly without bounce or loss of continuous contact. This paper describes the benefits of inclined pendulums in constant and variable tensioned systems such as creating a semi-constant tensioning effect, preventing current collector bounce and premature contact wire wear at the supports by reducing the uplift resistance on current collectors. It also provides the least visual obtrusiveness of all the suspension systems. In addition, this paper will present the associated costs of the inclined pendulum suspensions.

The primary purpose of this study is to use a nano-scale optical surface profilometer to assess the feasibility of such instruments in measuring localized friction coefficient on railways, beyond what can be commonly measured by tribometers used by the railroad industry. One of the important aspects of moving freight and passengers on railways is the ability to manage and control the friction between the rails and wheels. Creating a general friction model is a challenging task because friction is influenced by various factors such as surface metrology, properties of materials in contact, surface contamination, flash temperature, normal load, sliding velocity, surface deformation, inter-surface adhesion, etc. With an increase in the number of influencing factors, the complexity of the friction model also increases. Therefore, reliable prediction of the friction, both theoretically and empirically, is sensitive to how the model parameters are measured. In this study, the surface characteristics of four rail sections are measured at 20 microns over a rectangular area using a portable Nanovea JR25 optical surface profilometer and the results were studied using various statistical procedures and Fractal theory. Furthermore, a 2D rectangular area was measured in this study because 1D height profile doesn’t capture all the necessary statistical properties of the surface. For surface roughness characterization, the 3D parameters such as root-mean-square (RMS) height, skewness, kurtosis and other important parameters are obtained according to ISO 25178 standard. To verify the statistical results and fractal analysis, a British Pendulum Skid Resistance Tester is used to measure the average sliding coefficients of friction based on several experiments over a 5 cm contact length for the four rail sections selected for the tests. The results indicate that rail surfaces with lower fractal dimension number have a lower friction. The larger fractal dimension number appears to be directly proportional to larger microtexture features, which potentially increase friction.

General purpose railway tank cars similar to road tankers are known to transport liquid cargo in partial-fill state due to variations in liquid cargo density and governing axle load limits. It is widely reported that the cargo movements constitute additional forces and moments that could strongly affect the wheel-rail interactions and coupling forces, and thereby the directional dynamics of the wagon. In this study, the linear slosh theory is used to describe the liquid cargo movement in the roll plane by a simple pendulum, which is integrated into a comprehensive nonlinear multi-body model of a three-piece truck to study the effects of liquid cargo slosh on lateral dynamics of the tank car. The model also incorporates the nonlinear secondary suspension restoring and damping forces, attributed to friction of the wedges, using the non-smooth contact method in addition to the geometric constraints of various components. The wheel/rail contact forces are simulated considering non-elliptical wheel-rail contact using the FASTSIM algorithm. The lateral dynamic responses of the multi-body model of a freight car with partially filled liquid load and an equivalent rigid cargo are evaluated to study the effect of cargo movement on the critical speed and the wheelset hunting oscillations frequency. The results obtained considering different fill ratios of the liquid cargo suggest that the fluid slosh yields additional damping effect on the lateral dynamics of the car. Liquid cargo movement within partly-filled tank car could thus yield a beneficial influence on the wheelset hunting. This was evidenced from the phase relationship between the lateral oscillations of the pendulum and the bogie/wheelset. Consequently, a partially filled tanker resulted in relatively higher critical hunting velocity compared to that of the wagon with equivalent rigid cargo.

The current freight railroad operations are restricted to a maximum speed of 80 mph partly due to lateral instability of conventional freight trucks at higher speeds. The three-piece truck, a workhorse of the railroad industry for over 100 years, and its variations are susceptible to hunt at 50–55 mph when empty and 90–100 mph in loaded conditions. Design attempts to increase high-speed stability generally lead to diminished curving performance and increased risk of derailment. In this paper we describe a true pendulum suspension based freight truck that is designed to achieve stable operations up to 150 mph without compromising curving performance. The truck’s performance has been analyzed using an industry standard vehicle dynamics simulation tool. The AAR MSRP M-1001 Chapter 11 ‘Service-Worthiness Tests and Analyses For New Freight Cars’ were used to qualify the design where applicable. Traditional tread brakes are supplemented with axle-mounted disc brakes to provide safe braking capabilities beyond 110 mph. Two full-size 70-ton prototypes have been assembled using off-the-shelf and fabricated components. Yard tests have shown that the truck curves properly even under very tight curving conditions.