Constructing the Kurla flyover, workmen struck a gas pipeline belonging to Mahanagar Gas, which led to a leakage. At Goregaon last year, drills ruptured the Western Railway's underground feeder cables, disrupting power supply to the station.

A maze of subterranean utilities like electricity, gas and water pipelines, buried beneath the roads are proving to be irritating speed bumps in the Maharashtra State Road Development Corporation's (MSRDC's) high-speed, high-profile flyover programme.

That these utilities are virtually unmapped adds to their headache. ``We have been provided only directional maps by local authorities, which just indicate their general direction and not their exact location,'' says PL Bongirwar,MSRDC's joint Managing Director. Besides, some of these maps are old, practically useless considering many roads have been widened since they were drawn up.

So like oil prospectors of yore, flyover construction workers use the hit and miss technique, digging up the general area of the foundation until they come across some piped utilities.

Every conceivable utility from electric cables to water mains and phone cables runs beneath the roads, complicating construction, especially pile driving and foundation laying. There are four types of water pipelines: water mains, minor water supply lines, storm water drains and sewage lines. Even the slightest jerk could crack them as contractors have discovered. In the last two years, several such minor mishaps have occurred (EXAMPLES).

This has necessitated design changes. The under-construction Sion flyover, the most difficult of them all thus far, is a case in point. Amongst the city's oldest and most important traffic junctions, Sion is also an importantunderground conduit for thousands of cables.

Over a dozen piles were driven into the ground and abandoned before the contractors could find the right spots to erect nine-metre-high pillars. A single sewer line led to change in the design of the CST flyover inaugurated last month.

But the worst is yet to come. This problems on the western and eastern express highways could seem kidstuff compared to the maze of sub-surface utilities beneath city roads.

Staring at the MSRDC is a century-old storm water drain beneath the Mohammed Ali road, right in the path of the pillars for its two kilometre-long road over road. The corporation has proposed splitting this eight-foot-high six-feet-wide drain and shifting it to either side of the road.

However, anticipating such trouble, the MSRDC has cleverly included the provision for shifting these utilities in the tender clauses of flyover contractors. The big carrots being offered, Rs 1 lakh for each day of early project completion, naturally ensure that contractorswork double quick to rectify the fault. The delay doesn't last more than a couple of days.

And if its the bewildering array of utilities, then it's the sheer number of departments handling them. The BMC alone has 12 such departments. ``It took us three meetings just to identify the various authorities in charge of different utilities,'' says an exasperated MSRDC engineer.