Looking for Capacity Analysis w/ vs. wo/ twltl

[County]

I am trying to develop a standard for when to upgrade to multiple through lanes and/or include a two-way center left turn lane in a typical section. It seems that most capacity analysis on arterials deals with free flow speed and number of access points. I am looking for a technique, or better yet software, that would show me at what point a particular road needs upgrading. Using volumes alone would be easiest, but that seems that it could lead to both over and under designing.

Any ideas would be greatly appreciated!

 

[COLDAVE]

The solution isn't quite that easy. I recommend you use the Highway Capacity Manual and the software that emulates the process.

Deciding when to add lanes or when to convert from four lanes to three with a continuous left turn lane is subjective most of the time. The region in which you work may well have different comfort levels among the driving population than does another.

You should work with the University in your region that has an Engineering Extension Service from which you can gain a lot of information from the work of others. I use the HCM and the software that provides the similar results to manual calculation. Acceptable service levels vary with region and adaptability of the driving public. You will want to define service levels for your part of the world. Then you will have a better feel for when new lanes are needed.

Good luck with your quest! Traffic Engineering is still a bit of an art.