THE UTILITIES PROBLEM

Drive down any Austin street.  Look at the long, rectangular patches.  These are ‘street cuts' and they are a regular feature of utility maintenance.  Since water, sewer, gas, telephone, electric, phone and cable lines are run mostly underground, when it is necessary to service or repair these lines, cuts must be made in the street.

When the utility must repair these lines under the light rail, what becomes of the rail service?  Cars would have to be shifted from one set of tracks to the other, thereby slowing service in both directions.  Extensive switching must become part of the light rail line to enable them to shift cars from a south-bound to a north-bound track, and vice-versa.  

However much this slows the commute, it also slows the utility work since they can only go to the center of the light-rail line and stop, finish the first portion, then move to the other side and begin all over again, doubling the service time usually required.

However, the real problem of utility lines is what light rail electrical current does to them.  It corrodes them!  In Salt Lake City, this was a surprise result of their light rail, and every utility pipe had to be dug up and coated to prevent further corrosion.  See Utility Reconstruction for the University Light Rail, for an article where they try to sugar-coat this damage.  Likewise, in Austin, besides tearing up the street to lay rail lines, they would have to dig deeper for the entire route to uncover all utility lines, and coat them as well.

Cap Metro has made no mention of this in their planning.  Could it be that like Salt Lake City they were unaware of it? How much will this increase their cost projections?  If the normal track installation took a matter of 6 months on any given stretch, how much longer will it take to dig up every utility pipe at a much greater depth and specially coat it?  Will it have to be retrenched and laid even deeper than it was?  These are just some more of the unanswered questions Cap Metro has left us with.

From Utility Reconstruction for the University Light Rail:

'The first and most obvious difference is that unlike cars or buses, light rail trains  cannot be detoured around obstructions in the road when, for instance, a  water line breaks. Utilities which lie underneath the tracks must be either relocated or improved to minimize the possibility of breaks and mitigate the  need to tear up the road and shut down TRAX operations during routine or emergency utility maintenance.

The second, and less obvious impact of a new light rail system is a phenomena called stray current corrosion. Light Rail trains are powered by electricity. In basic terms, electrical current travels in a circuit from the power station to the train via the

overhead wires above the tracks, through the train’s electric engine, and back to the power station via the rail and ground. Electric current in the  ground will use the most conductive medium to return to the power station. Iron and steel water pipes are often good conductors. However, when the current leaves the pipe, it takes electrons with it and corrodes the pipe. To mitigate this problem, UTA is constructing a state-of-the-art system to minimize any stray currents. Furthermore, new water lines are being constructed with plastic materials (PVC and high-density polyethylene pipe) and/or protective coatings.  Included is a monitoring system to determine if any light rail stray current is getting onto the water pipes.'

LEAKAGE CURRENTS AND CORROSION

Leakage currents. The electricity supplied to the tram from the single overhead wire has to have a return path to the power source so that there is a complete circuit. This path is invariably through the metal rails on which the tram runs. Although tram rails are of large cross sectional area, they have to be made of hard-wearing steel alloy which gives them significant electrical resistance. This resistance can result in several volts difference in potential between the ends of a length of track when a large current is flowing .If one end of the track is well connected to earth, the other end has to be at some (small but unavoidable) voltage above earth. Under these circumstances, some of the current will tend to leave the track at far end, and other points along the track length, and find its way back through the soil. These currents are termed 'Leakage Currents. 'Leakage currents can be minimized by good rail bonding. Electrolytic corrosion currents through damp soil are a serious problem. As they enter and leave metallic objects, direct currents carry some of the metal of the objects into solution in the ground and the object is eaten away. The exact rate at which this happens will depend on the type of metal and the magnitude of the prevailing currents (which in turn depend on many other variable factors), but it is capable of wreaking considerable destruction unobserved if allowed to continue for a long period of time. Pipes, the metal sheaths of cables and the steel reinforcement in the foundations of buildings can all be attacked and it is a matter of great concern to any tramway to ensure that it is entirely blame-free in this respect. This problem was first tackled in the 1890s and the necessary precautions have been well known until recently.

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