2.0  Shoveling with Chemical treatment
This approach employs manual labor, snow blowers, and other mechanical devices to remove the precipitation.  Attractive features of this approach include: little or no capital cost, no added system to maintain, no appreciable increase in electric power demand, and no need for extra maintenance staff because available  contract   services provide a ready pool of laborers.  This approach, however, has several strong negative effects on the short term and long term structural health of the facility and on the life of capital equipment.

Use of corrosive chemicals to delay re-freezing of pavement has damaged vital escalator components, accelerating the deterioration of the platform, and threatens the substructure of the stations.  See Table 1 for summary of the system’s strengths and weaknesses and comparison with other systems.  The costs and effects of the chemicals on the station structure and capital equipment are often over looked.  This is because the deterioration process is not immediately evident.  The American Concrete Institute classifies an environment where deicing agents are present as a severe environment.  Typically calcium or sodium chloride is used as the chemical agent.  The chloride ions react with and break down the binding agent, cement paste, of the concrete.  Due to the relatively small size of the chloride ions, the deterioration moves through the concrete with each wet and dry cycle.  Eventually the chloride ions reach the reinforcing steel and rapidly consume it.  Once the adhesion is lost between the sand, gravel, and the reinforced steel, the concrete fails structurally.  The only solution left is to replace the concrete. 

The impact of corrosive chemical on concrete structures is demonstrated by the rate of deterioration of parking garages.  Parking garages are not treated with snowmelt chemicals.  However, these chemicals are tracked on to the premises by incoming vehicles.  The garages are generally constructed using a low water-cement ratio (f>45000psi), fly ash, and epoxy coated reinforcement to reduce the effects of salt.  Even with these precautions, the time to major repairs ranges from 7 to 15 years.  The major repairs include replacement of floors, beams, and columns.  Without this chemical exposure the life expectancy of the concrete is approximately 40 years.  MTA’s platforms are subjected to far more salt than parking garages and are less resistant to chloride ion penetration.  As a consequence, our platforms have to be repaired more frequently and suffer more rapid decline in structural integrity.  There are other chemicals sold as deicing agents that have even more destructive effects on concrete than salt.  MTA once used such chemicals, which resulted in structural failure in concrete members.

Capital equipment such as elevators and escalators are similarly affected by deicing agents.  Elevators and escalators at station entrances deteriorate from the bottom up.  A recent survey of these escalators exposed damaged base supports, and rust build-ups, resulting in deformation of crucial support members, and, in a few cases, actual shifting of the entire escalator assemblies were observed.  Thus, the total annual cost of using this method to clear snow and ice must include the hidden costs of major repairs or replacement of the infrastructure, inconvenience patrons suffer, and accidents.  Using our

10 freezing event for Baltimore, we estimate the annual cost to clear ice and snow at Owings Mills to be $88,000.  Details of this estimate are outlined Appendix, A.10.
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3.0  Overhead Infrared Approach
Infrared radiation is an electromagnetic emission generated in a heat source by rapid vibration and rotation of molecules.  The most attractive feature of Quartz lamp Infrared heaters is that it instantaneously provides radiant heat to melt snow without raising the temperature of the intervening air space.  The infrared fixture requires no more maintenance than would a fluorescent fixture, and the quartz lamps are rated for 5000hours.  The average duration of freezing precipitation is less than 150 hours per year.  Hence, the lamps will render many years of useful service.  With the infrared approach there is no refreeze of pavement.  Hence, there is no need for the use of corrosive chemical.  The system is equipped with temperature and relative humidity sensors.  Thus, it is automatically turned on some time before there is freezing precipitation.

Infrared fixtures are typically installed overhead.  Without a completely covered platform, a large number of fixtures would have to be mounted on poles.  The number of poles required could compromise space and the aesthetics of platform.  This is one of the drawbacks to the infrared approach.  See Table 1 for a summary of the system’s strengths and weaknesses and a comparison with other systems.  Another weakness of this approach is its high electric power demand.  For the Baltimore area, the system is required to output 90W/sq.ft to provide the desired result.  The total annual cost of using this method to clear snow and ice is estimated at $47,108.  See Appendix A.20 for cost derivation.
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4.0 Embedded System Approach
This approach requires implanting ferromagnetic tubes and or high resistance power cable in concrete, 2-4” below the finished surface of the platform.  The Direct Buried Cable and the Skin-effect methods are currently the most effective embedded systems in use.  Like the infrared approach, there is no refreeze of pavement.  Hence, there is no need for the use of corrosive chemical.  The system is equipped with temperature and relative humidity sensors.  Hence, it is automatically turned on some time before there is freezing precipitation.
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4.1 Direct Buried Cable
The Direct Buried Cable System is designed to deliver an average of 30w/ft.  A system designed to output 40W/sq.ft is generally required to yield the best result.  The fact that the cable is directly buried in concrete constitutes the system’s biggest weakness.  See Table 1 for a summary of the system’s strengths and weaknesses and a comparison with other systems.

      Correcting any fault in the buried cable would require jackhammering the concrete.  One weakness of this system, relative to the infrared system, is that much energy is expended to raise the pavement temperature before snow melting begins.  Other weaknesses include high installation cost and the potential for high repair cost.  Additional attractive features of this system include; low annual operating cost, very little maintenance requirements, and lower electric power demand than the infrared system.  The total annual cost of using this method to clear snow and ice is estimated at $44,340.  See Appendix A.30 for cost derivation.
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4.2  Skin-Effect Heating System
Skin-Effect heating system is designed to deliver 50W/sq.ft to the pavement.  It is best suited to large area applications.  The system is founded on the principles of electromagnetic induction and the skin-effect phenomenon that occurs in current carrying conductors.  Insulated conductors are used to heat the ferromagnetic tubes, embedded in the concrete.  The distinct advantage of this system over the direct buried system is that the cable can be pulled in and out of the tube in the event of a cable fault.

One weakness of this system, relative to the infrared system, is that much energy is expended to raise the pavement temperature before snow melting begins.  The biggest drawback to this system is its initial cost.  At $50/sq.ft this system is the most expensive on the market.  This cost does not include pavement demolition and reconstruction.  Another weakness is the potential for high repair cost.  Additional attractive features of this system include; low annual operating cost, very little maintenance requirements, and lower electric power demand than the infrared system.  See Table 1 for a summary of the system’s strengths and weaknesses and a comparison with other systems.  The total annual cost of using this method to clear snow and ice is estimated at $65,640.  See Appendix A.40 for cost derivation.
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5.0  Conclusion
The shoveling with Chemical treatment has been shown to be the most costly and inefficient of the approaches to control the accumulation of frozen precipitation on pavements.  It has been demonstrated that this method generates indirect costs that, in the final analysis, make it more costly than the most expensive automated system.  The inherent weaknesses of this method far outweigh its strengths.

The analyses also showed that the infrared system could be the method of choice based on its instantaneous heat production, lower annual cost than the skin-effect system, and low maintenance cost and requirement.  The advantages of the infrared systems outweigh its relatively high power demand.  The primary   drawback to the total use of infrared in platform application is the requirement for additional poles to mount the heat fixtures.  This problem would be eliminated if the platform were totally covered.

Of the two embedded systems discussed, the Skin-effect system would be the better choice for platform application.  The higher initial cost for the Skin-effect is compensated for by the fact that probable cable faults are much less costly to repair with the Skin-effect system.  The Direct Buried system falls short as an option because exception is taken to the prospect of jackhammering the platform to fix a cable fault.

Although our analysis suggests that automatic systems would be ideal for snow and ice control, they are not widely used in the Transit industry.  The current systems installed in the MTA are yet to receive unanimous acclaim within the MTA.  WMATA is still in the process of evaluating its needs.  Personal Rapid Transit, PRT, in Western Virginia, employs a hydronic system installed in 1971.  Reports indicate that the system is working well.  However, annual operating costs for the hydronic system range from $75,000 to $250,000.  Chicago Transit Authority, CTA employs infrared and other systems for snow and ice control.  The extent of the application of these systems could not be confirmed at this time.
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6.0  Recommendations:
The MTA should use an automated snowmelt system to control the build-up of frozen precipitation at its metro stations.  The infrared system is suitable for applications where the areas are totally covered with a canopy or the use of mounting poles would not be an exception.  A combination of the Infrared and Skin-effect systems for semi-covered platform applications, such as Owings Mills station could prove cost effective and efficient.
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