Transition lane lengths

[bbakk]

What guidelines might I follow for the following:

Beginning at a 4 way intersection my roadway width is 30' transitioning down to a 24' roadway width. I do not think that "L=[W(S)^2]/60" (20-25 mph) applies as I am not reducing the number of lanes or using the transition as a speed reducer or accelerator lane. I am assuming that I will be designing for comfort. Where might I find a typical transition guideline for this paticular case?

thank you in advance,

bbakk

 

[ishvaaag]

If you have the resources, design the transition as the code mandates...you won't be the sole one driving your roadway. Nor to say if there is some public body checking the design.

 

[CarlB]

The 'offset' in the transition formula applies to the travelled lane - so if your shoulder width is constant, the lane width transition is just 3' (15' to 12'), which gives you about 30' transition if I used your formula correctly. Another formula often applied is the 'speed:1' which would gove you 3x25 or 75'. These aren't very long transitions, and you may want to have them for reasons other than traffic safety (aesthetics, snow-plowing, etc.)

 

[chrisj]

I generally transition pavement widths at a rate of 30:1 when tying into an existing butt section on a road. That rate seems to work well on many roadway types and it is a smooth transiton.