236 To 644 Freebies!!

Actually, the afternoon southbound lanes are open to non-HOV traffic during HOV hours at the Turkeycock Run entrance ramp (located at the bottom of the hill between Duke Street and Edsall Rd). Non-HOV traffic must now exit at one of the next two exits south of the Turkeycock Run entrance ramp(either Va 644 Old Keene Mill Rd or the following exit which is the flyover for Backlick Rd or back to the regular southbound I-95 lanes). The third exit after the Turkeycock Run entrance ramp is at Va 7900 (the Franconia-Springfield Parkway), and it is "HOV-3 only" during HOV restricted hours. All three of these afternoon exits are from the left HOV lane.

It seems that the main reason the Va 644 HOV exit is open is it allows traffic to exit safely onto the two westbound lanes of Va 644. When cars exit off the regular lanes onto Va 644 westbound, those cars must do a "mixing bowl" across three lanes of heavy traffic already on Va 644 to get into the two left lanes that continue west of Springfield Plaza. It's much less dangerous to all Va 644 traffic to allow cars to exit off the Va 644 HOV exit.

It appears the late afternoon back-up at Springfield is caused mainly by cars entering the HOV at 6 PM from both Va 7900 and the entrance ramp from the regular lanes a short distance south of Va 7900. We've seen traffic backed up north to Va 644 because of that situation. Haven't really seen a back-up caused by the Turkeycock Run entrance or the Va 644 and Backlick Rd exits.

T'Rex,
That's true too.
Just pointing out that one possible reason the Va644 HOV exit remains open to non-HOV may be because the exit contributes to the safety of all traffic on westbound Old Keene Mill Rd.
Our carpool uses that exit most every day, and we don't see that it causes a backup problem on the HOV lanes. It appears to us that the major HOV backup problem is from traffic entering at the next two HOV entrances that I mentioned in my earlier post.
If VDOT does decide to change the Turkeycock Run (TCR) entrance to HOV3-only for now, that's understandable - and it won't impact our 4-person carpool at all since we enter HOV at the Pentagon.
But in the big scheme of things, the TCR entrance will be just another EZPass access point onto the HOT lanes. Then HOV-3, and those SOVs willing to pay the toll, can do the same thing they do today at that entrance.
Just pray that all the publicity about HOT lanes remaining FREE for HOV3+ is true as VDOT and DMV advertise.
Just curious as to what exact problems you have had at the TCR entrance & Va644 exit, and what time do you go southbound through there? Need more info to understand what you believe is a problem. We pass through there between 4:30 and 5 PM most days.

They have access from the regular lanes. It's Just not very convenient. Exit on Backlick then make an illegal U-turn and you're there.