"I'm not sure that an underpass, if intended for the light rail line and the vehicular traffic, would be any less disruptive, however, since it would probably need to be about as long."

That has essentially been METRO's stance, too, but it's simply not true. You don't need to look any further than the Fannin underpass at Holcombe, which has light rail and is approximately half as long as the proposed Harrisburg overpass.

Here's a summary I wrote previously for why an underpass would have significantly fewer impacts on the community. For some baffling reason, METRO did NOT take these points into consideration for their estimate of $67 million for an underpass:

1. Overpass will have to go over freight trains. Freight trains can be very tall, somewhere in the neighborhood of 22-25 feet. A bridge has to completely clear that. The tallest thing an underpass will have to clear are the light-rail vehicles, which require about 15 feet.

2. East Belt rail line is at a higher grade than Harrisburg. The freight tracks are several feet higher than Harrisburg. IE -- there's a bump there as you drive over the tracks. Those extra feet add to the clearance a bridge needs. Conversely, they take away from the required depth of an underpass.

3. ADA Compliance. A bridge cannot go any steeper than a 5% grade because the accompanying sidewalk can't be too steep for people in wheelchairs. The sidewalk of an underpass, however, is not constrained to the same depth/grade as the main lanes. Therefore, the slope of the underpass is determined by the light rail vehicles, which require a slope of no more than 7%. Steeper slope = shorter incline for a given height.

4. Caylor Street must remain open. Houston Armature Works owns warehouses on either side of Harrisburg and uses Caylor as an access road. Because of the above three considerations, a bridge will not be able to descend before Caylor and thus must remain in the air over Caylor. An underpass, because of the above considerations, will be able to reach grade by Caylor, and its length is thus unaffected by the need to keep Caylor open.

See, also, the discussion over at the Citizens' Transportation Coalition forums, starting approximately here:

http://www.ctchouston.org/forums/viewtopic.php?t=1254#4898.

The discussion includes reasons an underpass is preferable for the community as well as for light rail and urban development, and why an underpass could be feasible at this location.

I agree with all if Ian's points. Underpasses are always preferable to overpasses if there are neighborhoods nearby. But the specific conditions in this case make the difference more extreme than usual.

From the CTC forum:

Many civic and organizational groups in the East End have directed their energy and resources towards fighting the construction of METRO's proposed service and inspection (S&I) facility on land southwest of the intersection of Harrisburg and the UP rail line. The principle argument against the facility is that it will hinder the type of urban development that the neighborhood desires along Harrisburg. Developers have expressed their unwillingness to construct near the facility because of noise and the expected visual unpleasantness of the proposed building.

The hypocrisy is rather insulting. The S&I facility will be built at the existing Central City Industrial Park (formerly Hughes Tools). Does the name give you an idea of the type of development at this site?

Yet, it is OK for the East End Chamber of Commerce and Mr. Hlavacek to complain about the proposed S&I facility and at the same time feel compelled to protect Houston Armature Works. Can someone please identify these so-called developers that have a problem with the proposed S&I facility?

By the way, Houston Armature Works is owned by Lynn Woolley (a much respected business owner in the East End). His wife is State Representative Beverly Woolley and obviously Metro has made plenty accommodations to protect Houston Armature Works, even with an overpass scenario. No complaints here about that.

I have lived in the East End for 46 years and am very familiar with its residents. Folks from Second Ward, Eastwood and Magnolia that will depend on rail for transportation (unlike Mr. Hlavacek or myself since we are fortunate enough to own vehicles) could care less if it is an underpass or overpass. This is about mobility, especially over the UP rail tracks, which has been identified as the most blocked rail crossing in Houston. It is also about what is most cost effective -an overpass or underpass, especially in these economic times.

Excuse me Mr. Davila, but this is about more than merely protecting specific businesses or trying to achieve some vague idea of urban utopia. This is about creating transportation infrastructure that maximizes mobility for the community while minimizing destructive forces on impacted neighborhoods. It's also about making decisions that maximize benefits for the community over the long-term(say, 50-100 years), not just looking for the nearsighted, short-term, most "cost-effective" solution. On all of these fronts, an underpass wins at most urban rail crossings, and as Christof said, there are specifics at this site that make Harrisburg even more compelling than most.