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New Digital Speed Limit Signs on Freeway

Started 1 year ago by The Velvet Bulldog
Latest reply from datamuse

The Velvet Bulldog
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So, it seems that whenever I'm stuck in traffic moving 20mph, or not moving at all, I happen to notice those new digital speed limit signs telling me to slow down to 40mph. All I can do is shake my head and wonder, "HOW much money did the City spend on these??" I understand their intent--let drivers know there's a slowdown up ahead, and maybe from WS we're always merging into the worst of the I-5 Northbound slowdown, so the signs don't do us much good. But really, when traffic is stop-and-go, do we need this awesome technology telling us that it thinks we should be going 40mph? Have they been helpful for any of you?

Posted 1 year ago #
metrognome
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ok, first of all, it's the State, not the city. Second, the signs are part of a comprehensive effort to create a 'smart highway' system around the Puget Sound, which has one of the worst traffic overload problems in the country. Other parts of that effort include the overhead lane closure signs to divert traffic around stalls and wrecks, the traffic cameras, info available via smart phones, etc. Third, it appears altho the signs haven't yet helped reduce congestion, they have helped reduce rear-end collisions:

"A total 35 crashes occurred in the seven-mile stretch between Tukwila and Interstate 90 from Aug. 10 to Nov. 1, compared with a range of 100 to 140 wrecks between Aug. 10 and Nov. 10 the past five years ...

"Drivers are constantly asking what's the point of having a sign that says 40 mph, when I'm stuck in stop-and-go traffic?
....

The first answer, says McCormick, is that 40 mph becomes the legal maximum, and troopers have handed out speeding tickets. (Minneapolis' speeds are merely advisory.) As with any road, drivers must react safely to conditions. Nonetheless, even an inflated "40 mph" figure still gives a clue congestion is ahead.

Second, the signs can be only so precise. "A lane that was doing 30 a few seconds ago might be going 10. It's really dynamic," McCormick said."
from http://seattletimes.nwsource.com/html/localnews/2013373837_smartsigns08m.html

The story includes more details on the state's efforts to manage our freeways more efficiently.

Posted 1 year ago #
DP
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Thanks m-nome. (I was wondering the same thing as The VBD.)

I believe you formerly worked for the City of Seattle or something, doing some kind of PR or writing work, correct? I can tell.

Posted 1 year ago #
metrognome
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DP -- worked for Metro (aka King County); among other things, did a lot of writing (info pieces, letters for signature way way up the food chain) and research. Even tho I'm retired, I still scan articles on transportation. And thanks for the compliment ...

Posted 1 year ago #
The Velvet Bulldog
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mg: Thanks for the info and clarification! Apparently I couldn't find info because I didn't know what to call them, "Smart Signs?" Really?? ;-)

Appreciate the feedback!

Posted 1 year ago #
brew
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The thing that disturbs me about these "smart signs" is how they collect the information -

The travel times are calculated through license plate recognition. A traffic camera in one place records license plates of cars passing through its field of vision. A camera a little ways down the road does the same. The computer compares the two, calculates the elapsed time, which is displayed on the Travelers' Information Map. A set of dynamic signs hoisted above roadways in the city shows similar information to motorists.

Posted 1 year ago #
pigeonmom
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brew, the other day I received a survey in the mail regarding my travel habits in a certain sector of I-5. I'm sure this camera is how they tracked me.
Creepy.

Posted 1 year ago #
metrognome
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Velvet Bulldog -- I think we have given up on smart drivers and are relying instead on smart hiways. here's some more info from the WSDOT site: http://wsdot.wa.gov/operations/traffic (if you click on the little itty bitty 'Smarter Highways' under the pic on the right, it takes you to some useful info.
BTW, I apologize if my first answer was a little snarky, so I appreciate the thanks.

brew -- here's what the WSDOT website says about how speeds are calculated; monitoring license plates is not one of the methods they use:
"Traffic sensors along the roadway collect vehicle speeds, congestion information and traffic flow rates. This information is continuously relayed back to the WSDOT’s Traffic Management Center in Shoreline and analyzed by computers. When circumstances that would benefit from lowered speed limits—like congestion—are identified, the computer reduces speeds incrementally to gradually reduce the approaching flow of traffic to the congested area."
source: http://www.wsdot.wa.gov/smarterhighways/vsl.htm

pigeonmom: curious if you can provide more info on who sent out the card or who the survey is being done for. License plate surveys are routine and have been used for years to identify a pool of people to survey when more traditional methods can't be used. Not too much different than Safeway or Costco (or any other store with a member's card) tracking your purchases ... or is it? The state has adopted pretty stringent guidelines on use of this kind of data.
http://apps.leg.wa.gov/RCW/default.aspx?cite=42.56.330

Posted 1 year ago #
pigeonmom
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Yes, I understand all that. This was sent by Thurston County Regional Planning Council.

Posted 1 year ago #
brew
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Metrognome - Actually the WSDOT site did have info regarding the license plate scanners several weeks ago but that info was removed. Why? I don't know, but I did read it there myself.

My quote came from here - November 16, 2010 entry, 4th paragraph down -
http://www.digitalcommunities.com/blogs/city-cio/

Backed up by SDOT's site, 3rd paragraph down -
When the system is completed in March, there will be 22 dynamic information signs, 80 vehicle license detectors (to collect travel times), 130 traffic cameras, solar-energized traffic volume counters, upgraded computer-controlled traffic signal equipment, and fiber optic connections

http://onthemove.seattle.gov/2010/10/18/real-time-travel-times-helps-travelers-make-smart-choices/

Posted 1 year ago #
metrognome
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brew -- the two articles you linked to are about Seattle DOT's system, not WSDOT's. Neither mentions what they do with the images of the license plates; so I checked SDOT's site:

"License Plate Reader Systems - uses CCTV technology to scan license plate numbers to measure the travel time along a corridor. The system is set up to have an entry point and an exit point that create a cordon. When a vehicle enters a cordon its license plate number is recorded. If the vehicle goes all the way to the exit point its license plate number is recorded again as well as the time the vehicle took to travel through. This data averaged over many vehicles creates an accurate picture of current travel times. Once the travel time data for a vehicle is recorded the license plate record is discarded."

http://www.seattle.gov/transportation/its.htm

I also searched WSDOT's site for 'license plate reader' and got 5 hits; the only useful one was a presentation about using cameras for traffic studies.

Posted 1 year ago #
hooper1961
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from what i have heard the dynamic freeway signs have improved safety. 40+/- mph is the speed when the maximum capacity is achieved; and in many cases it also indicates the freeway is congested and operating poorly. thus it my suspicion that 40 mph is the defacto minimum that is used

my primary issue is why the signs are limited to 60 MPH maximum when the majority of the freeway is designed for 80. There are times during the summer evening (daylight, light traffic and dry) where freeway design allows for a 70 MPH limit. admittedly the times are rare and simply being able to actually travel at 60 MPH is nice

Posted 1 year ago #
waterworld
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Well, Hooper, you do know why the signs only go up to 60 MPH when 60 is the maximum legal speed on a stretch of highway, don't you? I respect your analysis of traffic and roadway issues given your credentials, but it is hard for me to believe you don't understand the concept of a limit imposed by law as opposed to sound engineering criteria. My sense is that you understand the legal limit, but you disagree with it.

Posted 1 year ago #
waterworld
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oops, hit the button twice...

Posted 1 year ago #
johnnyblegs
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You know what would be very useful with these "smart signs"? Letting me know when the EXPRESS LANES are open. I rarely travel on I-5, but when I do it's when I'm going north to the Skagit Valley. I've lived here all my life and for some reason I can never keep it straight as to when they're open. It would be very helpful to notify drivers as they travel north in the carpool lane that the express lanes are good to go. I think this would greatly reduce all the last minute merging that happens closer to the downtown core.

BTW: the speed numbers they post are bunk. How does that reduce accidents? It just shows me which lane to switch to. But that could actually increase collisions.

...and why aren't there the same signs going SOUTH? Seems they could have taken a few of them off the north lanes and put them on the other side. I mean...do we really need them every 100 yards?

Posted 1 year ago #
metrognome
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johnnyblegs -- there are no signs going south cuz chupacabras only go north (to get away from the WS raccoon gangs).

I'm glad you asked about the hours, cuz I go to Edmonds on weekends:

Monday-Friday
Southbound - 5 a.m. to 11:15 a.m.
Northbound - Noon to 11 p.m.
Closed: 11:00 p.m. - 5 a.m.

Saturday & Sunday
Southbound - 7 a.m. to 1 p.m.
Northbound - 2 p.m. to 11 p.m.
Closed: 11:00 p.m. - 7 a.m.

there are also changes in hours for special events:
http://www.wsdot.wa.gov/Northwest/King/ExpressLanes/SpecialEvents.htm

There is an open/closed sign about mile from the entrance but it is after the James St bypass off-ramp, so it's too late to take an alternate route. If there is a logjam, it can be faster to take the Seneca off-ramp, turn right on 6th and then right at the next intersection which becomes an on-ramp; this helps avoid the bottleneck (shhh ... don't tell anyone else or they'll all use it.)

So, where would you like to see a sign about whether the lanes are open or closed? Your only alternate route is the Viaduct. I think I'll e-mail WSDOT to see what they say.

The speed numbers are the same for all lanes; the message boards advise of lane closures and you can be ticketed for continuing in closed lanes. The variable speed postings reduce accidents by alerting people to slowdowns ahead that they can't see because of the hills and curves or talking on their cellphone or whatever. Much of the congestion in caused by accidents, not solely by traffic volume.

Posted 1 year ago #
johnnyblegs
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Thanks metrognome. I've never known the migration paths of the chupacabra. It's nice to get that cleared up (:

That's always been my gripe about the closed sign for the express lanes. Why notify drivers 1 mile out? I though this would be remedied with the expensive new digital signs installed on I-5. I think the first one is down by Boeing Field. It'd be nice to know back there. And why not a sign on the WS bridge and even the Columbia/Spokane street onramp from Beacon Hill. The city is trying to improve traffic flow right? What about the folks bypassing the city exits and just driving straight through?

Posted 1 year ago #
nuni
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they seem like another distraction for already distracted drivers.

Posted 1 year ago #
GAnative
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metrognome - "The speed numbers are the same for all lanes...".

Are you saying that all lanes have the same speed at the same time? Because they don't; at 8:34 this morning the last smart sign before the I90 exit said 40mph for all lanes except the far left which was 50mph. I wasn't quick enough to get a picture because for one we were doing the speed limit. :)

Posted 1 year ago #
metrognome
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GAnative -- you were right about what I meant but apparently I was wrong or that sign malfunctioned. My understanding is that the same speed limit must be applied to all lanes in a stretch of road but it could be I misread whatever it was I read or ... as I recall, the far left lane is an HOV lane, so maybe it is permissible for a different speed limit to apply to that lane. I was gonna e-mail WSDOT about johnnyblegs question, so will ask about that too.
And, thanks for not taking a picture if you were the driver.

Posted 1 year ago #
WorldCitizen
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I've seen different speeds on different signs within each group as well.

Posted 1 year ago #
JoB
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me too

Posted 1 year ago #
metrognome
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I've read thru the WSDOT Smarter Highways site til I'm cross-eyed and there is no mention of different speeds in the same stretch of road; however, there were two pictures of a different speed in the HOV lane than the regular lane; here's one:

http://wsdotblog.blogspot.com/search/label/Smarter%20Highways

the best rule of thumb is that the *maximum* speed limit for the lane you are in is the speed posted on most recent sign you saw.

Posted 1 year ago #
datamuse
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I too saw a different (higher) speed limit for the far left HOV lane on NB I-5, near the I-90 interchange.

I would guess that since the HOV lane is usually less crowded it might often have a higher speed limit.

Posted 1 year ago #