Best Ways For Expressway Lane Merges?

[bluecountry]

So on the NJTP headed south at exit 4, the road shrinks from 3 lanes SB to 2 lanes with the rightmost lane becoming the exit lane.  Meantime, headed northbound at exit 4, the road increases from 2 NB to 3, with the new right lane forming as exit 4 merges onto the road.

On the other hand, in VA on I-64 as it shrinks from 3 lanes each way to 2 lanes each way, the right 3rd lane continues past the exit, with in fact a 4th lane added from the interchange merging down to 3 then 2 lanes.  When going east from 2 to 3 lanes, 64 adds the 3rd lane before traffic from the interchange has merges, so in fact when traffic from the interchange is added it goes to 4 lanes with a merge to 3.

My question, isn't the best way to transition from 2 to 3/3 to 2 or any increase/decrease in expressway lanes to simple have it done at the exit, like with NJTP where exiting traffic takes the right lane, and entering traffic adds the right lane, this way there is no merging?

[Dirt Roads]

My question, isn't the best way to transition from 2 to 3/3 to 2 or any increase/decrease in expressway lanes to simple have it done at the exit, like with NJTP where exiting traffic takes the right lane, and entering traffic adds the right lane, this way there is no merging?

NCDOT may have been thinking that lately.  Historically, the merge point on I-40 westbound leaving Durham was just beyond the Orange County line (which is located just before the westbound onramp connection at Exit 270).  The leftmost lane dropped at about the same location as the end of the onramp, (sometimes) forcing four lanes of traffic to squeeze down to two lanes.  Fairly recently, NCDOT changed the lane drop such that the right lane exits for US-15/501, and the left two lanes only have to deal with (sometimes) heavy onramp traffic downstream.

Indeed, this works much better at all times of the day (albeit, rush hour congestion is now as early as 2:30PM).

[webny99]

Ideally a lane drop at an exit would be an exit only lane so that slower exiting traffic is on the right. In addition, traffic from the right lane that merges left will now be in the new right lane, instead of traffic merging left being in the new left lane. This only works as long as there is enough traffic exiting that the loss of a lane on the mainline doesn't cause backups. If backups are occurring, it's better to extend the lane on the mainline and have it end beyond the interchange so traffic can use the available lane and zipper merge.

Ideally a lane being added at an entrance would open up on the left of the mainline. That way traffic will default to the right and center lanes and only shift to the far left lane as needed to pass, and if there is no entering traffic, the left lane should remain open for passing.

Admittedly, this mixes the two different types of merges which some may see as inconsistent, but it is optimal to prepare drivers for the shift to having one more or one less travel lane and to promote KRETP as much as possible.

[triplemultiplex]

Adding or dropping a lane at an exit is the best solution only if there's a good bit of traffic using that exit and it's easier to give exiting and entering traffic its own lane.  Otherwise, it's best to add and drop lanes on the left.
I see the latter more often around here where the extra lane gets added to the left as one approaches the next interchange.  And then in the other direction, the left lane ends a little ways past where the onramp merges.

I see that as generally better because you're not forcing 'thru' traffic to merge.
Though this gets more tricky in urban sections with busier exits so it's not always the best solution.

[bluecountry]

So maybe this is why on the NJTP, the 3rd lane is used as exit only since a lot of traffic leaves but on I-64 WB the 3rd lane continues past the interchange?

You think when merging from 3 to 2 lanes (or any merge) it is better for the far left to be the lost lane than the right?

[Dirt Roads]

You think when merging from 3 to 2 lanes (or any merge) it is better for the far left to be the lost lane than the right?

I grew up at a time where we were taught that "The car on the left always has the right-of-way".  That rule applied to four-way stops, on-ramps (with or without yield signs), and switching lanes on multi-lane highways.  I think that it is fair to say that this rule no longer applies in many of these situations, and in some cases, folks are taught the exact opposite.  (My uncle who was much older wasn't taught that rule back then, either).

Anywhoosit, for those designers using this as a rule of thumb, lane drops in the far left lane both allows the fast lane to overtake the middle lane, plus allows for the construction of the additional lane in the freeway median without requiring a zig-zag at the merge point.  But in West Virginia, we are accustomed to right-side additional lanes that are specifically marked as "Truck Lanes" (ergo, climbing lanes).

If your main consideration for Best Ways For Expressway Lane Merges? is short-term costs, the left-side solution is a no-brainer.  But someone in another thread recently mentioned that this construction technique gets messy when the freeway needs a complete reconstruction of the original lanes.