Our decaying infrastructure that's really too young to be decaying: Big Dig light fixture hanging by a thread

Hanging by a thread

UPDATE: State officials are blaming an "oversize truck" for taking out one of those lane-marker things, BostInno reports - so yes, it's always September in the O'Neill Tunnel.

Somewhere in the back of the mind is a vague memory of state officials promising to do something about all the Big Dig light fixtures held up by library paste or paper clips or something. Jason Porter managed to take a picture in the northbound tunnel this morning that suggests they missed at least one.

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Nope, no signs on chains.

But they do have overheight detectors prior to the tunnel entrances that a) activate warning signs for the approaching drivers and b) send an alarm to the tunnel control center, who then notify the State Police.

Plus, the clearance in the O'Neill Tunnel is only 13'-9" from top of roadway to bottom of anything hanging off the ceiling. As max legal height for trucks in Massachusetts without a permit is 13'-6", that doesn't leave much room to account for a shift or bounce in the load, especially given how the tunnel roadway grade changes (containers and car carriers are notorious for this effect).

Is there any leeway? In

Is there any leeway?

In some states, clearances are actually a foot higher than the signs say.

Of course, that causes problems when truckers assume there's an extra foot, and then there isn't.

As I understand it, the only "leeway"

in the Big Dig tunnel clearance is that the 13'-9" measurement is from the roadway to the bottom of the stuff hanging from the ceiling (like those signal lights and overhead signs). So, the actual vertical clearance of the tunnel "box" itself from roadway to ceiling is probably closer to 15'-5".

As a point of reference, Federal standards for "low clearance" signs on highways generally require the posted clearance on the sign to be at least three inches less than the actual clearance. However, I've never seen (or heard of) any instances in Massachusetts or other states where the difference between the sign and the actual clearance is a foot or more.

Yeah, let's bury all the roads!

Just in case nobody gets it, we have constant teaching moments that burying Interstate highways underground is not worth the much higher complication, cost, maintenance, and number/severity of problems compared to even elevated roadway.

Wiki lists Interstate highway specs as having 14' minimum vertical clearance in urban areas, 16' rural, plus allowance for repaving layers. So, the $14B tunnel will continue to be an exception to standards, resulting in more events. The difference isn't as bad as Storrow drive, but we can expect more events to come.

Over height sensors were installed for a reason - tunnel being below spec. I wonder what the point of them is beyond just making it easier to find the time to search video recordings. I would hope there might be loud warnings and visual sign warnings to stop, both on the road and in security and control centers.

When an over-height truck

When an over-height truck passes the first over-height sensor heading toward the tunnels, all the big LED message boards activate and warn the driver to exit or pull over. If they ignore the warnings and pass the second set of over-height sensors, the state police is dispatched to catch the violator. Alarms also activate at the 24/7 MassDOT Operations Control Center in South Boston. I learned this on a recent tour of the Operations Control Center.

Nice theory

That all seemed to work as well as the $100M intruder alert system at JFK or Ronald Reagan's Start Wars anti-missile systems. Low tech is sometimes still the best solution. $100M could have paid for human patrols for a long time.

Box truck being towed did it?

I was trying to imagine what vehicle would be high enough to take out the signs. Video from yesterday's power line down across the Interstate showed one of the trucks being towed. It was high flat bed with a shipping container on it. So, a 13' truck on the hook of a (big) tow truck certainly puts it over 13'9" high.