work zone speed reductions at large 1

[Drumchaser]

Would like to throw this out there and receive comments on how effective some of you all think this is. Our standards have taken some of the teeth out of using these, by making them harder to acquire.
Not looking for MUTCD qoutes, just general opinions, instances of success, failure, problems etc.
Speed is routinely the root of most performance issues in our work zones. Long-term and short-term reductions.

Thanks

 

[ACtrafficengr]

WZ speed limits face the same problems as any other speed limit: to be effective, you have to make the driver believe that the appropriate speed matches the speed limit. One way to do this is draconian enforcement.

About a decade ago, I saw a TRB article about attempts to reduce speed on I-10 near Houston. The only thing that had any affect on speed was narrowing travel lanes to 10'. On two-lane roads, 10' lanes are associated with 50% increases in run-off-road, sideswipe and head-on crashes.

Maybe you need to look at it the other way, and see if you can design your work zones to accommodate the travel speed on the roadway. Easier said than done, I know, but that might be the reasoning between the change in your standards.


"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[Drumchaser]

Amen on the Draconian. Have been on the Katy frwy. when the lanes were narrow and it felt like nine ft....not good at all.

Thanks for your comments.

 

[teeman]

My own guideline is WZ traffic control should be designed for the prevailing operating speed. A speed reduction might be justified if significant (more than 1 ft) reductions in lane width are necessary to maintain the number of required lanes. In general reductions in posted speed limits should be avoided.

 

[LCruiser]

teeman has it right - you need to design for the prevailing speed. Draconian measures increase speed differentials. Speed differentials are more dangerous than speeding per se. The speed limit should be set at the 85th percentile speed, which just happens to be the 1st std. deviation. Most drivers are used to driving at the speed the roadway is designed for. Artificially lowering that speed is dangerous and could make you liable in a court of law for an accident. Follow the MUTCD - that's your best and safest bet. The FHWA has literally billions of dollars of research on this subject - besides, then they become the deep pocket. If you don't follow the MUTCD you and/or your client become the deep pocket.

 

[Drumchaser]

LCruiser

Thanks for the great comments. Here comes a curve.

Visualize:
A controlled access high speed facility w/heavy truck mix.
2-lanes in each direction w/depressed median.
Lane closure will be needed for daytime operations.
While the closure is intact delivery trucks will be exiting into live traffic every 10-15 minutes or so while operations are in the inside lane closure.
You cannot design for the prevailing speed here.

You see....there will exist a speed differential regardless. The challenge then becomes how to effectively deal with it.
Is a speed reduction prudent here?

 

[LCruiser]

Certainly, I would say a speed reduction based on the geometry of the entrance ramp. Speed differentials are much less important when there is no passing available

 

[Drumchaser]

Sorry, let me add some details.

The entrance ramp does not come into play. The del. trucks are leaving the closed lane (inside lane) and exiting the WZ into the live lane at 10-15 minute intervals.
Oh yea, the capacity of this rdwy is maxed out even when no work is present.

any takers?

 

[teeman]

Speed limits are meant to define the border between reasonable and unreasonable behavior on the part of motorists operating under "ideal" conditions. Under congested conditions speed limits have no meaning.

An intermittant entry into a lane where stop&go conditions exists does not have the same hazard as a heavy vehicle trying to enter high speed flow in an adjacent lane. A common WZ practice is to have arriving trucks exit the adjacent lane downstream of the WZ and back into the WZ. The gap created by arriving vehicle can also be used by exiting vehicles.

Motorists need to know if they are in a lane that may need to accommodate an entering construction vehicle. Access to and from the site is an element of the WZ design that needs to be considered during the design process.

 

[Drumchaser]

teeman

Well spoken. Highly relevant comments. Your descriptive sequence in and out of the WZ is very real time and utilized as much as conditions will allow.

Congested conditions are not happening upstream a mile or so.
Driver expectancy on this rdwy is high speed hammer down. Rolling terrain. Generally rural.
The ebb and flow of the distant upstream que is the concern.
And the PCMS's and WZ speed drop would be to give timely advance warning to conditions ahead.

Is a daytime speed reduction prudent here?

 

[teeman]

I don't see reduced speed limits as having any real advantage unless you physically cannot negotiate the geometry of the WZ at the posted speed in good weather and uncongested traffic flow conditions.

Most modern high speed roadways have sufficient sight-distance for a motorist to recognize the presence of a queue on the road ahead. If queues extend past the advance warning signs on a regular basis, I would add additional signs at a point in advance of the queue.

We have tried to divert traffic from corridors under construction by posting informational signing in advance of bypass routes. The signs indicate the presence of construction in the corridor, the start date and a message to consider alternate routes.

 

[Drumchaser]

teeman

Again, your comments are germane.

This facility is not new or modern.

We also have tried to inform John Q of impending WZ's at key points of possible diversion, with some success.

The use multiple PCMS's (portable changeable message signs)
in advance of the WZ, to give sufficient warning, seems to be most effective.

Thanks again for your comments.

 

[Drumchaser]

Thanks for all the comments.

Okay, what I would really like to see is "actual" instances of use of WZ speed reductions. Anything ranging from expressway to two-lane (one-lane flagger TCP) facilities would be great.

Please no manual, policy, or organizational rhetoric.

You actually employed the reduction(s), and the good or bad of what transpired.

Input on the “actual results” of use of advisory speed plaques would be great as well.

And as is the usual case (of maintenance type work), the zones are not usually designed; they are existing facilities where standard TCP's are utilized with the addition of other measures to enhance the specific needs of the situation.

Thanks