While the incidence of rail bridge issues is relatively small, the media have not paid much attention to the simple fact that our highway infrastucture has been put under intensifying pressure due to more liberal size and weight restrictions.
When I graduated from college in 1971, the maximum length permitted for a highway semitrailer in my native Pennsylvania had just been increased from 40 to 45 feet. That figure has since been raised twice more, and now stands at 53 feet. Gross vehicle weight restrictions have been increased from 73,000 to 80,000 pounds. and the diminshed suitability of the rail network for "high and wide" moves has opened the door for much bigger loads if authorized by special permit.
Preliminary indications are that the bridge in question was not under a particularly heavy stress, but I'm still waiting for confirmation. It's worth noting that in the days of steam, some rail bridges necessitated the separation of double-headed power by the use of idler cars. And as a very heavy load crosses a truss bridge, the stresses shift to different parts of the structure. Multiply that by the chance occurrence of two or three heavily loaded 18-wheelers spaced close together and moving in the same direction -- who knows?
If any suitable response comes out of this tragedy, I would hope that our media would do a better job of informing the public how badly our transport infrastructure has deteriorated, and how much greater a cost will be occasioned by our "gotta-have-it-yesterday" attitude toward distribution.
Last edited by 2nd trick op on Fri Aug 10, 2007 2:14 pm, edited 1 time in total.
What a revoltin' development this is! (William Bendix)