101/Woodside Interchange - Other Promising Alternatives Considered

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Three alternatives to the Preferred Project were considered “Promising Alternatives” and evaluated in the Project Approval & Environmental Document (PA & ED) phase of work. The Promising Alternatives included some common elements, which are listed below.
  • Addition of through lanes on Woodside Road/Seaport Boulevard at the interchange.
  • Reconstruction of all ramp connections between US 101 and Woodside Road/Seaport Boulevard, including additional vehicle storage and turn lanes, and new signalization at ramp intersections.
  • Construction of a flyover ramp providing a direct connection between Veterans Boulevard and US 101.
  • Construction of bikeways, including Class I (shared use (bike/walk) paths), Class II (bike lanes), and Class III (bike routes), on Woodside Road and Seaport Boulevard between the intersections of Woodside Road and Bay Road and Seaport Boulevard and East Bayshore Road/Blomquist Street.
  • Construction of sidewalks, ranging from 6 feet to 10 feet in width, with associated crosswalks with standard safety features, on Woodside Road and Seaport Boulevard between the intersections of Woodside Road and Bay Road and Seaport Boulevard and East Bayshore Road/Blomquist Street.
  • Addition of turn lanes at the intersections of Broadway and Bay Road with Woodside Road, and the intersection of Seaport Boulevard and East Bayshore Road/Blomquist Street.
  • Construction of a Class I Bikeway (shared use (bike/walk) path) adjacent to the Union Pacific Railroad (UPRR) drill track serving Seaport Boulevard industries. This bikeway is subject to approval by UPRR, and would connect the intersections of Veterans Boulevard and Chestnut Street and Seaport Boulevard and East Bayshore Road/Blomquist Street.
  • Construction of Class I Bikeways (shared use (bike/walk) paths) on each side of the Veterans Boulevard flyover ramp between Chestnut Street and Woodside Road, which would connect with existing sidewalks and Class II Bikeways (bike lanes) on Veterans Boulevard.

The other promising alternatives considered are summarized below. These were evaluated against the No Build Alternative, which assumed no major improvements within the Project area other than routine rehabilitation and repair.

Alternative 3A - Roundabout with Diamond Interchange
(click image to enlarge)

101-84-Alt-3A-small


 As shown in the exhibit above, this alternative was a variation of the Preferred Project that would construct a roundabout instead of the signalized intersection at the northbound US 101 ramp intersection. The roundabout offers the benefits of continuous vehicular flow and reduced vehicular conflict points, with yield control rather than signals at its entries. The other features of this alternative would basically match those described for the Preferred Project except as noted below.

Vehicles exiting northbound US 101 would bypass the roundabout to reach Seaport Boulevard and points east, and enter the roundabout to reach Woodside Road and points west. Vehicles on Seaport Boulevard entering northbound US 101 would bypass the roundabout and enter US 101 on a ramp very similar to the existing one. A loop on-ramp similar to the existing one would serve the eastbound Woodside Road to northbound US 101 movement. Through traffic in both directions would use the roundabout.

Alternative 3B - Partial Cloverleaf with Diamond Interchange and Broadway Grade Separation
(click image to enlarge)

101-84-Alt-3B-small

 As shown in the exhibit above, this alternative was a variation of the Preferred Project that would lower the through lanes on Woodside Road west of US 101 so they cross under Broadway, which provides the benefit of reduced vehicular conflicts and improved intersection operations. The existing at-grade Broadway intersection would remain in place and continue to serve through traffic on Broadway and turning movements to and from Woodside Road.  The other features of this alternative would basically match those described for the Preferred Project.

Alternative 8B - Diverging Diamond Interchange
(click image to enlarge)

101-84-Alt-8B-small

 As shown in the exhibit above, this alternative would replace all existing US 101 ramp connections with diagonal ramps in a diverging diamond configuration, a relatively new but proven design whereby Woodside Road would be reconfigured to allow eastbound and westbound traffic to cross to the opposite side of the road and back again at two new signalized “crossover” intersections, one on each side of US 101, to efficiently serve conflicting traffic streams. These two signals can operate very efficiently because they serve only two phases of traffic (eastbound and westbound Woodside Road). Also, this alternative limits vehicle conflicts at signalized off-ramp intersections because each one of these junctions serves only one direction of Woodside Road traffic rather than both.

This alternative would add sidewalks on both sides of Woodside Road and Seaport Boulevard except between the Woodside Road crossover intersections, where a Class I Bikeway (shared use (bike/walk) path) would be constructed in the median of Woodside Road. The Class I Bikeway would connect to outboard sidewalks via crosswalks at the crossover intersections. The Class I Bikeway would continue east on the south side of Seaport Boulevard to connect to the intersection of Seaport Boulevard and East Bayshore Road/Blomquist Street.