For you Seattle, WA folk...

[wisp2007]

For years, this empty sign bridge on I-5 in Seattle has piqued my curiosity. 
I do know there was a sign on here, because old photos showed a sign once stood there, but I have never been able to see what that sign was ^^ If there's anyone who can help me, or who remembers, that would help me a lot

[Alex]

Seattle's freeways about to get smarter

Starting next year, new electronic signs along Interstate 5 and State Route 520 will alert drivers when there is a collision or traffic slowdown ahead. The signs, which will rely on a network of sensors, are part of the "Active Traffic Management" system, or what state transportation officials call "smarter highways."

The signs will be placed every half-mile on three corridors. The locations and activation dates are:

    * Northbound I-5 between Boeing Access Road and I-90 in summer 2010.
    * SR 520 between I-5 and 130th Avenue Northeast in Bellevue in summer 2010.
    * I-90 between I-5 and 150th Avenue Southeast in Bellevue in spring 2011.

Already, WSDOT is building overhead sign bridges along I-5. The signs will be installed every half-mile.

Alternate speed limits will be posted above affected lanes, or signs will show when a lane is closed. Drivers who don't obey the alternate speed limit could be ticketed, Charlebois said. (WSDOT has this video to show you how it works).

[Chris]

Interesting. We have that on many freeways in the Netherlands, and now other countries are picking it up too.

We have it since 1981.

It reduces accidents in the tail of a traffic jam.

The problem over here is that they abuse the system to enforce ridiculously low "environmental" speed limits, such as 50 mph on freeways that would otherwise be posted at 60 or 75 mph.

[KEK Inc.]

Seattle's freeways about to get smarter

Starting next year, new electronic signs along Interstate 5 and State Route 520 will alert drivers when there is a collision or traffic slowdown ahead. The signs, which will rely on a network of sensors, are part of the "Active Traffic Management" system, or what state transportation officials call "smarter highways."

The signs will be placed every half-mile on three corridors. The locations and activation dates are:

    * Northbound I-5 between Boeing Access Road and I-90 in summer 2010.
    * SR 520 between I-5 and 130th Avenue Northeast in Bellevue in summer 2010.
    * I-90 between I-5 and 150th Avenue Southeast in Bellevue in spring 2011.

Already, WSDOT is building overhead sign bridges along I-5. The signs will be installed every half-mile.

Alternate speed limits will be posted above affected lanes, or signs will show when a lane is closed. Drivers who don't obey the alternate speed limit could be ticketed, Charlebois said. (WSDOT has this video to show you how it works).

That new system is utilizing the newer steel sign bridges.  The sign the original poster was referring to is an older 1960-1980 style lattice structure sign bridge.  While it's possible that this sign may have been preserved for the new traffic system, the question still remains as to what was on the sign.

[KEK Inc.]

Here's a photo I took of the new speed limit system, actually. 

[Scott5114]

Hm. Does the "speed limit must be the same in all lanes" rule that FHWA espouses not apply to HOV lanes?

[KEK Inc.]

Hm. Does the "speed limit must be the same in all lanes" rule that FHWA espouses not apply to HOV lanes?

Technically, this sign is supposed to allow different speeds for different lanes.  Say there's a wreck in a lane...  They would reduce the speed for the lane being merged onto.

[Bickendan]

Where is this?

[KEK Inc.]

Where is this?

NB I-5 at around mile marker 162 (just before I-90).

[Scott5114]

Hm. Does the "speed limit must be the same in all lanes" rule that FHWA espouses not apply to HOV lanes?

Technically, this sign is supposed to allow different speeds for different lanes.  Say there's a wreck in a lane...  They would reduce the speed for the lane being merged onto.

Yes, but that's against the Word of FHWA. I remember CA tried a thing with a different speed limit above each lane and FHWA got all fussy with it and made them stop.

[J N Winkler]

Yes, but that's against the Word of FHWA. I remember CA tried a thing with a different speed limit above each lane and FHWA got all fussy with it and made them stop.

My memory is different (or perhaps we are thinking of different incidents).  In the early 1960's Caltrans tried lane-by-lane speed limits to see whether that would lead to a more favorable distribution of vehicle speed across lanes--slower traffic in the right lanes, faster traffic in the left lanes, each lane faster than the one to the right of it, etc.  The lane-by-lane speed limits were found to have no useful effect on traffic distribution and the final report concluded that they served no useful purpose.  FHWA was not involved at all (strictly speaking, it did not exist at that time because it had not yet replaced the BPR).

Does the MUTCD have chapter and verse forbidding lane-by-lane speed limits even in dynamic contexts?