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Wednesday, May 6, 2009

Variable Speed Limits – What’s the deal?

MoDOT is currently in a two-year study on the use and effectiveness of Variable Speed Limits (where traffic engineers raise and lower the speed limits based on how fast traffic is moving). Since the project was implemented in May 2008, the department has surveyed drivers and collected speed data. The media is reporting on preliminary findings of that survey (which include the fact that at this point, law enforcement and drivers are not convinced of its effectiveness).

As one of the people sitting in on developing the criteria for the study, I have to admit that this was completely expected. One of the items I hoped to see as part of the study was a change in public opinion through the two-year project. This is a brand-new idea to the St. Louis area -- using variable speeds to manage the volume of traffic flow through congested areas is completely new, and people don’t like change they don’t completely understand.

This early data from this study helps MoDOT determine what it’s doing correctly and what it isn’t. For instance, one of the big areas that drivers and law enforcement both stress is that they don’t believe the public is as informed as they need to be about how variable speed limits work. That’s a great point, and something that MoDOT (and I) need to look at. So – we have a website that talks about how the project works, we have a flyer that we handed out, and we’ve put spots in the media. What else do you suggest? I’ll consider any reasonable request (especially if it’s cheap (since we are a state agency.))


Jason H said...

not the right spot, but I assume someone will read this. WHOS BRIGHT IDEA WAS IT TO CLOSE THE HANLEY BRIDGE AND BIG BEND BRIDGE AT THE SAME TIME???? idiots

And variable speed limits suck. I will tell you why. NOBODY does 60. I drive a rig and flow with st. louis traffic everyday down 270, which is usually about 70 mph. 60?? Really? Most cars are capable of 120mph. 60 should be criminal.

MODOT CR STL said...

Jason H –

Let me assure you that the closure of both Hanley and Big Bend was discussed and debated extensively before Gateway Constructors and MoDOT determined to simultaneously close the overpass.

Both Hanley and Big Bend Bridges are a significant portion of the rebuilt section of I-64 between Kingshighway and I-170. Both bridges are in the way of the new roadway and have to be reconstructed. Big Bend had to close June 1 to ensure that the entire east half of the roadway is completed by the end of the year. Hanley has been closed since the beginning of this year and we anticipate that the work on the Hanley Bridge and interchange will be complete by August. The contractor is working as hard as possible to complete the Hanley Bridge as quickly as they can. Additionally, now that both bridges are closed, we are monitoring the traffic flow and making adjustments to signals as needed to keep traffic flowing as smoothly as possible.

As far as your comments about Variable Speed Limits, the limits are designed to be implemented during times when congestion is building on I-270 – primarily during morning and evening rush periods. The speeds are reduced in the section of roadway prior to the congestion, in an effort to keep the congestion from growing and creating gridlock. We cannot make people obey those limits – all we can do is educate and continue to educate people that if they speed through areas where the limit is reduced, all they are really doing is speeding toward potential gridlock. Variable speed limits do work – they have been proven in other portions of the country and overseas. They do require people to adhere to them, to work correctly.

Andrew G.

t.lodholz said...

Variable speed limits are an ineffective and dangerous tool.

1. The limits change too rapidly during peek hours. It has been observed that limits can vary buy 20 mph in just a mile of highway. As some drivers quickly break to adjust to the new limit, others traveling faster can slam into the rear end of the breaking vehicle.
2. Common sense tells that the safest way to drive on a highway is having everyone moving “with the flow of traffic”. A slower moving vehicle becomes an obstacle to other drivers. This is a very dangerous situation.
3. Take you eyes off the road. If you are in the left lane and a truck is along side you in the right lane, you can’t see the signs.
4. “Shake down” tool for local police. Maryland Heights in particular is reaping the benefits by writing tickets to confused drivers as these shifting limits change throughout the day.
5. It doesn’t work. After a million dollars of tax payer money, no significant change has occurred.

I don’t like the way drivers on 270 speed, but anyone who has lived in St. Louis knows people drive fast on 270, it isn’t going to change. Now you add extremely low speed limits and you turn drivers into dangerous road hazards. It is good in theory, but I not going to risk my life. I will continue to drive at a safe speed, and if that happens to be 60 mpg in 40 mpg, so be it.

Modot states that people “don’t like change they don’t completely understand”. Well MODot needs to understand that drivers shouldn’t have to risk their lives to safe them a few bucks.

Anonymous said...

I tried this 45 mph tonight on 270. Three signs were 45 and I was the only one doing it! I saw everyone fly by me! I felt VERY UNSAFE! IF I GET IN AN ACCIDENT DO I GET TO SUE MODOT!?! Once I got to 270 & 170 the highway was all blocked up and the speed limit was posted @ 60mph! Who could do that noW that we were all in a jam!? Get rid of it... a Pilot program doesn't last for YEARS... This pilot has crashed... pickup the pieces and move on!

MODOT CR STL said...

Jeff --

Thanks for your comment -- I can understand your frustration with driving at 45 mph and having other vehicles pass you. They did, however, contribute to the jam that you experienced, because they didn't moderate their speed.

Why did the sign say 60 mph in the middle of the jam, then? Well, we adjust the signs based on the traffic ahead of you -- I would venture that once the vehicles got out of the jam, traffic moved fairly quickly (as evidenced by the 60 mph ahead sign). It was somewhat self-regulating (the jam regulated the traffic), but people would move much faster if they actually paid attention to the variable speed limits (and obeyed them).

You can see this for yourself. Take a funnel, a jar and about a half a pound of rice -- pour the rice in the funnel and watch how the rice (traffic) creates its own jam. If you regulate the speed by which the rice (traffic) pours into the funnel, you can get the rice through the funnel faster. The same thing happens on the natural choke points on Interstate 270.

One might say, then, to build a bigger funnel -- that's a reasonable idea, but building larger roads still cost a lot of money (and don't necessarily get rid of the natural choke point). So, building a larger road would fix the problem for a short time, but then more traffic would use the road and would create the same issue (only larger).
The VSL program was a two year program to help alleviate congestion issues during the I-64 closure -- and once the closure was finished, we would be evaluating the project for its effectiveness. We are still evaluating it. Initial results show that there was some improvement to traffic flow on the sections where the variable speed limits were implemented.