Weaving vs. Ramp Junctions

[kevparker]

Could anyone tell me the advantages over a weaving section vs an on/off ramp junction section. I have analyzed both alternative, but the LOS is higher for the ramps. This does not make logical sense?

 

[johnp]

Hi kevparker,
Glad to see you are still in charge of the mathematics, and not the other way around. If the answer doesn't make sense, it usually means that some of the built-in assumptions are wrong, or some of the fudge factors have not been verified for your range of application.

I suggest you forget the mathematics for a while. Go to a weave section with a stopwatch, and a Video Camcorder. Then do the same for the on-off ramp. Then you have some real hard data to base your decision on. And check out for safety issues while you're at it. Weaving is OK if you have polite drivers, but can be hard yakker if some are pig headed.

Regards - Sgt John Rozentals
University Regiment (retired)

http://www.latviantourists.com.au

Johnp.Rz

http://www.mets.net.au

 

[DMcGrath]

I was involved in some design review / value engineering for a major interstate corridor, and a "weave" type interchange was something the design group tried to avoid if at all possible. Sorry I don't know the mechanics behind it, but weave was almost a four letter word to this group.

 

[ACtrafficengr]

Weaving sections have more conflicts between vehicles, and therefore often have safety problems. Drivers are trying to get on, off and throough at the same time. Since humans are not really that good at doing more than one thing at a time, mistakes are made.

Since separate ramps reduce driver workload drivers make fewer mistakes.

"...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

 

[civilman72]

Not that I'm an expert traffic engineer, but I believe it comes down to the number of conflict points with other traffic...

To get on or off a standard on/off ramp, you have unimpeded flow, whereas with a weaving section you must deal with traffic doing the opposite of you (i.e. if you are exiting, you are crossing the drive path of those entering). So, becasue an on/off ramp configuration has less conflicts than a standard weaving section, the LOS should be better.

 

[cvg]

we have a weaving junction about a mile from the office. Ramp is going onto the freeway. After going up the ramp, either weave left to freeway A or stay in the lane to go on freeway B. Cars from freeway A can then weave right to go onto freeway B. It's a constant struggle to get on either freeway after going up the ramp and avoid the high speed cars attempting to weave right. I don't see very many accidents there, however in heavier traffic it comes to nearly a complete stop every time.

 

[kevparker]

Thanks, everyone. The insight has helped me to look at the problem a little differently. I just couldn't see how three through lanes with on/off ramps could be more efficient than three through lanes connected by an auxillary lane.

The calcs from the Highway Capacity Manual don't make logical sense to me, but they are empiracal and based on a sufficient amount of research.

Thanks.