Climate Considerations

Introduction
Snow and Ice Handling Issues
Hot weather Issues
Salt Use and System Implications
Impact on Maintenance, cleaning and storage of vehicles
Power Supply System Implications
Conclusions

Introduction

The technology and vehicle selected for use on Ottawa’s rail rapid transit network will have to be capable of operating in the harsh winter climate, as well as the heat and humidity of the summer months.

Ottawa can experience extremes of temperature of -36.1C (recorded in 1943) to + 37.8C (recorded in 1944). In addition to these extremes of temperature the effects of humidity and wind chill can exacerbate these temperatures and cause further extremes of - 47.8C (recorded in 1968) and +46C (recorded in 1955)1.

Reliable data on the occurrence of rapid temperature swings is not easily found, however reports and observations indicate that this is a common regional phenomenon, which will lead to increased moisture production on vehicles. The rapid change of extremes of temperature is known in the industry as ‘thermal shock’ and can typically induce early mechanical and electrical failures if the designs have not accommodated appropriate tolerances and margins.

Table 1 - Ottawa annual temperatures

Extremes of temperature significantly affect the operation of equipment and in the case of mechanical components can expand with heat or contract with cold. Electrical systems take more peak power with colder temperatures or can overheat and/or shutdown with higher temperatures.

With any technology the control of temperature is critical to maximise equipment performance and reliability. It should be noted that the verification of temperature extremes is very difficult to analyse and appropriate measures should be in place to ensure that the manufacturers warranty is not compromised.

The on-board equipment as well as the tracks, power collection and stations need to be robust enough to handle the heavy snowfalls, freezing rain and ice, and freeze-thaw cycles. While a fully winterized system can be developed, the system also has to operate during the heat and humidity of summer, introducing additional challenges.

The scope and nature of the issues, along with the implications for the vehicle technology are summarized with some potential solutions that have been adopted by other “winter cities”. The discussion is based upon known solutions in operating systems as well as requirements identified from literature reviews and specified standards from the American Public Transportation Association and other relevant standards bodies.

Range of Issues

There is a range of issues facing the deployment of rail vehicles in severe climate conditions such as those experienced in Ottawa. These include:

• Snow and snow handling issues (ploughing, storage and removal);
• Ice formation, snow, freeze/thaw, freezing rain and their removal;
• Salt use and system implications;
• Impact on maintenance, cleaning and storage of vehicles;
• Mechanical fouling due to expansion in heat;
• Mechanical failure or fracture due to rigidity or contraction in cold;
• Increased equipment unreliability due to poor cooling in extreme heat;
• Increased passenger discomfort in climate extremes;
• Increased maintenance /replacement;
• Increased power consumption due to Heating and ventilation controls compensating for poor thermal management;
• Catalyst for corrosion;
• Thermal shock of equipment; and
• Poor lubrication leading to increased wear.

Ottawa has some experience in this regard, having successfully operated the diesel-powered O-Train since 2001. Conversion to an electric system operating, within a variety of potential different corridor types (e.g. grade-separated, on-street, elevated), will require additional considerations, as outlined below.

Snow and Ice Handling Issues

There are four main issues related to snow and ice handling that need to be considered;

• Accumulation during a single snow event, wind-blown snow
• Accumulation over the course of the season,
• Formation and removal of ice, and the
• Melting snow both during and at the end of the snow season.

Cities with comparable winter conditions where LRT is deployed such as Calgary, Edmonton, and Salt Lake City (Utah) use a variety of techniques to ensure continuity of service with snow conditions. These are specific to a type of vehicle and would need to be considered, and properly specified, for the vehicle that will be procured by Ottawa.

Different vehicle types also have design constraints that will influence their winter performance, primarily related to clearance issues and their power source.

Snowploughs on front car of trains

Salt Lake City deploys cars with snowploughs on the front of each of the trains during snowfalls, and Ottawa’s Talent Trains have shovels permanently installed at each end of the trains, which assists with keeping the tracks clear. As with the City maintenance vehicle fleet, the ploughs would be installed in late fall and removed at the end of the snow season. These will add weight to the vehicle and may require specific structural modifications to the vehicle. The added weight will reduce performance, but avoids the need to have specific snow fighting equipment.

Ice Controlling Pantographs

The power collection pantographs on the top of the vehicle are designed to clear power contact wire of ice. As the train moves along the line they scrape the bottom of the contact wire, removing the built-up ice. In normal operation only one of the pantographs is used for power collection, while the others are retracted. In severe winter weather the additional pantographs can be extended up to increase the number of contact points, assisting with ice control. The pantographs also push the wire up, flexing it assisting in breaking off the ice.

Heated pantographs are also standard on the Salt Lake City fleet. The pantographs make contact with overhead electrical lines powering the trains. Salt Lake City also installed additional heated pantographs on several of its trains, designed to act as a “powerless spare” sending heat up into the contact wire, thereby reducing ice build up.

Automatic Switch Heaters

Sensors are installed in critical or all track heaters that come on automatically with a combination of moisture and temperature to ensure switches do not ice up. Many systems reported that where there are not automatic switch heaters, they deploy staff to clear the switches manually during snow conditions. There are a number of switch heating mechanisms on the market but these fall into two categories, gas powered or electrically powered. Electrical heating is provided by attaching a resistive element against the rail and thermostatically switching the device. The element has to be sized for the Ottawa environment and the heatsink properties of the rail. The element effectively warms the rail during cold periods. This heating system requires some electronic control systems that can manage a number of heaters. Gas powered heaters can be obtained into two formats; localised heating, where the ignited gas is held against the rail to keep the metal warm and the more general purpose heater which focuses the heat in a general rail area. It should be noted that the gas heater tends to be more effective, but can cause widespread melting and then freezing outside of the heat boundary. Propane gas is potentially a lethal and explosive fuel and therefore carries some risk of use in and around the track areas.

Continuous Operation

One of the simplest and most effective approaches, used by many transit systems, is to operate trains continuously over the line during snowstorms in order to keep tracks clear and de-iced. The movement of the trains moves the snow out of the way. This operation would continue during overnight periods when there is no revenue service. For example Vancouver, Salt Lake City, Calgary, Edmonton and Baltimore report this type of operation with their rail systems. This type of operation can also involve additional maintenance crew responsible for riding the trains and clearing switches, wires etc. as necessary.

Vehicle Clearances

Several of the available vehicles will require more attention to snow and ice removal in their standard configuration. For example, vehicles that use a Linear Induction Motor (like the Vancouver SkyTrain) have very limited clearance under the vehicle body. To operate properly the gap between the bottom of the vehicle and the LIM Rail is only a few centimetres. In Ottawa’s climate, this could very quickly be filled with snow, which can be compressed and heated and turned into ice. Similarly ground level power pick-up systems also require low clearances that could intensify winter mitigation measures.

Specialized Snow Vehicles

For major snowfalls, specialized rail mounted ploughs may be required. These vehicles would be used to clear the tracks and maintain service.

Door operation

Areas of ice fouling risk will be in the door areas where snow and ice can accumulate and compact causing the door to remain open and therefore inhibit vehicle movement. Special consideration regarding door track clearing, heating or the use of ‘plug-type’ doors should be given.

Platform edge doors

As with hot weather the platform edge door also maintains the station temperature closely to that of the interior of the vehicle and prevents and rapid fluctuations.

Braking systems

The electro-hydraulic/electro-pneumatic brake system is exposed to the extremes of temperature at all times. With electro-hydraulic system the hydraulic oil emulsifies and becomes less effective in an electro-pneumatic system the compressed has considerable water content that must be dried otherwise the water will freeze and the brakes will fail on. It is common in humid climates or climates that have rapid fluctuations in temperature to have either air-dryers or water separators fitted.

Traction control (Spin/slide)

An important development in vehicle design is the ability to monitor the revolutions of the traction wheels against the non-driven wheels. This allows two important control mechanisms to take place in the vehicle. A decrease in revolutions at the driven wheel against non-driven mean that the vehicle brakes have caused the vehicle to enter a ‘slide condition’, therefore increasing wear on the wheel and track.

An increase in revolutions at the driven wheel means that the driven wheel has lost traction and will need to deposit either sand to gain traction or reduced power at the driven wheel.

The performance of this system should not be underestimated for Ottawa. The spin detection allows the vehicle to accelerate quickly out of a station under all conditions. While the slide detection reduces maintenance, decreases stopping distance while increasing safety for the passenger.

Electrical Loads and switching

Of significance is the low temperature effect of electrical resistance. As decreases with lowering temperature the start-up currents and power consumption will be greater during winter. The vehicle equipment design will have to take this into consideration.

Moisture removal

Within the vehicle there will be areas that interface between a colder body and the warm interior, such as displays and equipment cupboards. Some of these areas will require thermostatically controlled anti-condensation heaters that will operate at preset temperatures to ensure that the temperature drops does not induce condensation. It should be noted that in extreme case of high humidity, there are some moisture absorbent paints available which will provide the same function.

Hot weather Issues

The high humidity and high temperatures of the Ottawa climate pose some additional challenges to the designer of the vehicle and its equipment, which is largely in the form of the management of the vehicle cooling and the dissipation of excess power generated as heat.

Any LRV will generate a large proportion of waste heat from a number of sources:

• Braking resistor (if fitted).
• Braking system.
• Air conditioning.
• Electrical and mechanical equipment.

Neglecting the effects of humidity, when outside of the tunnel the vehicle generates waste heat and releases this into the ambient environment whereupon it is dissipated in the air; this is known as convection.

However in the tunnel areas the vehicle will dissipate heat into the ambient environment of the station surroundings once stopped. In the height of summer this can be a considerable temperature rise if unmanaged.

As such the station heating and ventilation and air conditioning (HVAC) will need to be sized to be able to cope with the transient heat rises expected from the vehicle when stationary. Not only is this for the comfort of the passengers but also the longevity of operation of the vehicle equipment. It should be noted that some modern stations actually recover the waste heat and pump this into heat recovery or storage systems for operational buildings or facilities.

To isolate the interior of the vehicle from rapid changes in temperature some stations provide platform edge doors that effectively assist with maintaining temperature inside and outside the vehicle.

Humidity in addition to high temperatures adds further to the extreme environment as heat transfer technology or the process of convection is less efficient. The general approach to this is to ensure that train and equipment cooling mechanisms can cope with the maximum temperature and humidity for long periods when undergoing tests and evaluation of performance. Equipment should be appropriately de-rated and in most cases should be able to tolerate failure of the cooling system for short periods of time until detected. There are several railway standards that mandate testing that would emulate the Ottawa environment; one particular standard (EN50155) would be suitable for use or adaptation and would not be unfamiliar to vehicle manufacturers.

Salt Use and System Implications

Many winter operating properties reported the use of anti-icing and de-icing programs at stations, platforms and associated parking lots. The Rail Safety and Standards Board in the United Kingdom has the most recent study on the different materials that can be used and their impacts on LRT systems.² This 2005 study finds that a variety of materials are used by rail systems ranging from Rock Salt to Glycol.

The research identified two distinct areas within station areas that influence technology, namely platforms and parking lots. The study did not specifically address track use as they noted it was not specifically deployed on tracks and it was difficult to isolate the kind of product used along an entire track due to different methods being deployed by different cities etc. The cheapest option of rock salt was deemed appropriate for station parking lots as they are large areas to treat and run-off would be unlikely to affect the track. The number of metal structures present is limited and the surface is normally tarmac, rather than concrete, therefore corrosion is not a priority in this area.

The report noted that the most sensitive areas to treat are the platforms. For these it was suggested acetates would be the most suitable de-icers. A potassium acetate product applied in liquid form and a sodium acetate product in solid form is recommended as the most appropriate. These projects are seen to be less expensive than Glycol, but also less damaging to the track and station infrastructure than rock salt.

The report also noted that as well as the de-icer product, the application rate is also important. Therefore, is recommended that appropriate spreading equipment be used rather than ad hoc spreading in order to control the spread rate of the de-icer. Health and Safety requirements also need to be considered both during application of the product and also during storage. Correct storage of the selected de-icer product is also important in order to maintain its effectiveness and ease of application.

In platform heating options can also reduce the amount of snow and ice control needed at the platform as can increasing the percentage of the platform that is covered and protected from the extremes of weather. Platform heating can be selectively used for stairs and stair landings as well as portions of the platform that are exposed to the elements, however the source of heat energy and the inefficiencies of heating outdoor areas have a negative impact on overall energy use.

Covering the tracks and platforms for all or most of the platform length can substantially reduce the amount of snow and ice that needs to be removed or melted. This has an initial capital cost associated with providing the cover, but reduces long term maintenance.

The prime concern with de-icing agents is their affect of inducing rust and corrosion in vehicle bodies, corrosive effects on the door mechanisms and floors inside the vehicles, cleaning and maintenance impacts, and the potential impacts that contaminated water could have on vehicle power and communications systems. The physical effects on vehicles can be mitigated through the use of aluminium car bodies, regular cleaning and floor materials that are resistant to the corrosive effects of the chemicals used, however the impacts on power and communications systems are more difficult to address.

The ingress of saline water associated with the melted snow will exacerbate any corrosion on metallic surfaces in close proximity to the water. Many modern vehicles have inner compartments that have sealed floors that assist in maintenance and cleaning and help to reduce the corrosive impact of saline water. However the mix of the warm environment and the saline water will always serve to create an ideal corrosive environment. Fixings and fastenings through this floor should be minimised to ensure that the water does not channel through the body shell but also improve cleanability. Floor slopes should be added to assist drainage and positive drainage should be provided to ensure the liquid can escape. This concentrated saline water should then be dispersed below the vehicle in a strategic area where the solution cannot contaminate equipment below.

Rock salt contamination in switches can cause the device to impact operations either by not closing, or to seize due to poor lubrication. Regular maintenance during winter periods to ensure the mechanism is clear of contamination will minimise the impact of the rock salt or the addition of automatic lubrication will assist in reducing corrosion. One further aspect of corrosion is the build-up of rust on the rails that leads to poor track circuit detection. As such the vehicle may requires appropriate track circuit detection that can operate with some rust contamination or be fitted with a rail scraping mechanism to remove some of the oxide layer.

In electric rail systems, the electrical current returns through the running rails, and circuits to control train movements (connected to the signal system) also use the running rails. Salt water, particularly with high concentrations of sodium and chlorides, can interfere with these systems by allowing power and signals to “leak” to ground. This can affect the signal system and introduce stray currents into the adjacent ground.

Impact on Maintenance, cleaning and storage of vehicles

Maintenance and Cleaning

Winter operating conditions are reported to require additional inspection and some additional maintenance for vehicles, including the need for:

• Additional inspection of doors to remove ice build up and ensure seals are operating properly for both regular operation and to ensure against moisture leakage.
• Waterproof or water resistant housings for electrical systems to stop “Fluffy” snow from entering into the electrical system from the underbelly of the train causing a short in wiring.
• Additional inspection of air filtration systems to prevent snow penetration.
• Additional inspection of control system heating vents to ensure working properly during winter with no snow or ice build up.
• Additional part inspections and replacements for gaskets and undercar electric boxes.3
• Some properties operating in winter conditions report the need to clean floors of vehicles more vigorously in the winter months and the need to have or add heaters at door entries for both low floor and high floor vehicles to prevent slipping. Drainage of the snow melt in the compartment area will be a challenge, but regular maintenance, lubrication, the use of plated or stainless steel fixings will reduce the effects of corrosion. Under floor equipment should be painted with protective paints such as 3M’s ‘Copon’ and care should be exercised in understanding the electrolytic properties of the interface of fixings and fastenings to ensure that dissimilar materials are not used.

Additional design and maintenance consideration for winter operations include:

• Avoiding steep grades immediately adjacent to sharp turns, which can potentially impair the vehicles braking ability in ice conditions. Grades (incline or decline) should also be avoided anywhere a vehicle must regularly start or stop, for slippage concerns.
• Need for preferential snow clearance on track that is flush with street, particularly for low-floor vehicles. Snow needs to be kept out of the tracks and if the tracks are flush with the street will collect in the tracks. Locations where track is higher than surrounding area helps to protect against this issue. Although open switches are preferred, particular attention must be paid to drainage when there are in-street switches.
• Water lubricants (if needed to control wheel squeal at tight turns) cannot be used in the winter and a substitute is required.

Indoor Storage

While manufacturers report that vehicles do not need to be stored indoors, many systems that operate in extreme cold or heat conditions store vehicles inside in order to ensure the on-board systems and temperature are sufficient for quick deployment. In particular, Calgary noted that when there is insufficient storage for vehicles, the pantograph is connected which allows them to run an auxiliary heater to the interior. Power also allows the traction and other vital electronics to be under current. This generates enough warmth to facilitate the needed functionality of the components otherwise start-up can be very sluggish.

Some systems use tunnels or covered stations for storage of trains during winter non-operating periods to help prevent snow and ice issues. Tunnel storage may require staff monitoring by the city Fire Marshall.

The vehicle will inevitably be exposed to some severe thermal swings in its daily and annual schedules. A combination of adequately specified equipment, careful design and thorough maintenance and operating procedures will assist in limiting the effects of climate on the vehicle.

The Ottawa climate will necessitate the storage of the LRV in some form of temperature controlled and enclosed environment. An unprotected vehicle will be subjected to large thermal swings from low temperatures associated with overnight storage back up to ambient temperatures. This rapid change in temperature gives rise to high internal humidity and increases power consumption at start-up.

One method of mitigation is that the vehicle can be left powered through the storage period, however there may be safety issues related to leaving the vehicle powered and unattended, even in a reduced power mode.

Storing the vehicle outside and the consequential exposure to the outside elements will incur time penalties in start-up durations and therefore running costs; as the vehicle will take longer to prepare for service. Furthermore, external storage will not be conducive to regular inspection during the winter periods.

The placement of the vehicle in a covered storage facility has a number of benefits:

• LRV is maintained at ambient temperature and therefore only uses minimum power to adjust its internal temperature when running outside.
• Ease of maintenance and inspection.
• Less thermal impact on equipment and components.
• Maintains manufacturer’s warranty.

Power Supply System Implications

In addition to the potential issues related to the selection of the vehicles, the power systems also have winter issues. Ice build-up in particular, will impact the design and look of the system. Each of the potential power supply solutions will be impacted in different ways:

• Catenary poles and the design of the messenger and catenary wires need to consider the added weight of ice build-up over the course of an event. Ice can add substantial weight to the poles and wires, and must be considered in sizing the poles, wires, mechanical fasteners, tension systems and related hardware.
• Third rail systems are susceptible to snow build-up and drifting snow, which can interfere with electrical contact, and ice can build up on the third rail. The weight of ice and snow is not generally an issue as the supports and size of the third rail is sufficient to support the added load.

While the Traction Power SubStations (TPSS) are not susceptible to snow and ice issues due to their enclosure in protected rooms, the electrical supply that feeds the TPSS requires redundant connections to ensure reliability of supply in the event of an Ice storm or delivery system failure. As such it is normal for the electrical power provider to implement redundant connections or a form of redundancy scheme that can ensure electrical supply to the system throughout extreme events. As electrical systems require additional power in the lower temperatures associated with Ottawa’s winter the system will require design to accommodate the additional demands required.

Conclusions

The extremes of winter and summer in Ottawa, introduce significant challenges to operating rail-based transit. The specific conditions will require stringent specifications to be developed, derating of components and appropriate design margins to deliver and maintain a reliable and cost-effective system.

The clearance under vehicles, the design of the power collection system and the use of de-icing materials represent the most significant issues to be addressed. Ample space and clearance, as well as careful control of snow and ice are required. The vehicle selected, along with the power system to operate it are equally important in determining the future direction for Ottawa.

¹. Source Environment Canada

². Rail Safety and Standards Board, Evaluation of Frost, Ice, and Snow Precautions at Stations, Project T532, 2005.

³. APTA, Volume 2-Vehicles Inspection and Maintenance, Recommended Practice for Heating Ventilation and Air Conditioning Periodic Inspection and Maintenance, February, 2002.