Phase 2 Alternatives Jun 13, 2008 12:12:50 GMT -8
Post by darrell on Jun 13, 2008 12:12:50 GMT -8
I see two basic criteria, what I'll call lane flow capacity and queuing length.
* Lane flow capacity is limited by stopped time at signals. For example, a standard lane can carry X vehicles per hour through an intersection where the signal is red 30 seconds out of a 60-second cycle.
The exercise in Monday's presentation for Overland said there is 25 minutes of red time per hour at Ashby.
Stopped time for crossing gates overlaps part of that red signal time, resulting in their conclusion of 32-33 minutes of combined signal and gate-down red time per hour.
That reduced flow capacity (from 35 minutes per hour to 27 minutes per hour green time) per lane would be mitigated by adding a third lane coming up to the intersection on each side.
Less green time per lane x more lanes = more total time.
Same for Sepulveda, adding a third southbound lane to mitigate increased red time at the Exposition Blvd. intersection / crossing.
* Queuing length is simply whether stopped cars would back up across a grade crossing. Can't have that!
For example, Bundy queues all the way from Pico to Olympic in both directions, here shown at the right-of-way, and will have a bridge.
The concept for Barrington is to add right-turn lanes in both directions. That third lane in each direction shortens the queue length at Olympic and Pico by as much as 1/3.
With three different traffic engineering consultants looking at this, their analysis must be pretty bullet-proof.