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Antonio Area Roads
INFO: Harry Wurzbach at Austin Highway
page last updated June 1, 2018
Location: Harry Wurzbach at
This project will build an interchange connecting
Harry Wurzbach to Austin Highway to replace the disjointed access there
now. Exit and entrance ramps will connect from Harry Wurzbach directly
Austin Highway at the existing overpass location. The new
interchange will include San Antonio's first Single Point
Urban Interchange (SPUI).
elongates a standard access road intersection so that the two intersections
by the access roads on each side of the overpass are instead compressed into a
intersection located on the middle of the overpass. To do this, the
access road approaches are bent inward so that the left turn movements
can pass-by each other like they would at a typical surface street
opposing left turn movements on each axis of the intersection to
simultaneously like they do in a typical surface street intersection,
the number of signal phases required (fewer phases = fewer delays.)
Right-turns still take place at the same location as they do in a
conventional intersection. However, with a SPUI, there is no
traffic on the access roads (i.e. you cannot exit Harry Wurzbach and
re-enter it by going straight through to the entrance ramp.) At this
location, since there are entrance and exit ramps and not true access
roads, there should be no need for anyone to go straight through
the diagrams below for a visual depiction of a SPUI as compared to how
a conventional intersection at this location would operate.)
will be the first SPUI in San Antonio and, from what I can tell, just
the third one in Texas. The other two are in North Texas in Plano and
McKinney and a couple have also been proposed in the Houston area. The
design, however, has been around since the mid-'70s and is in
widespread use in many other states and overseas.
diagrams below show what the traffic flow for a conventional
intersection would be versus that for a SPUI.
FLOW FOR AUSTIN HWY.
SINGLE POINT URBAN INTERCHANGE (PROPOSED)
TRAFFIC FLOW FOR AUSTIN HWY.
FLOW FOR HARRY WURZBACH LEFT TURNS TO AUSTIN HWY.
SINGLE POINT URBAN INTERCHANGE (PROPOSED)
FLOW FOR HARRY WURZBACH LEFT
TURNS TO AUSTIN HWY.
accomodate the SPUI, the existing overpass will be expanded. The extent
of that expansion varies by quadrant.
addition to the ramps and SPUI, this project will also make the
following other changes:
signal on Eisenhauer just west of Harry Wurzbach at the current access
road will be removed and left turns at that intersection will be
prohibited and blocked by a concrete island. (With the new ramps to and
from Harry Wurzbach, there should be little need for those turns
anymore.) The right-turn ramp from the access road to Harry Wurzbach
will also be removed; drivers will still be able to make two right turns at that location to get onto southbound Harry Wurzbach.
signal on Harry Wurzbach just south of Austin Highway (providing access
to the Lowes and HEB) will be removed. A dedicated left turn lane into
the rear driveways of both stores will be provided. Motorists can also
use the new ramps to Austin Highway and then access those stores via Austin Highway.
current "front" driveway for Lowes at Harry Wurzbach will become an
exit-only drive as it is located where the southbound entrance ramp
from Austin Highway will be; traffic coming from there will turn onto that ramp.
driveway to Discount Tire on Austin Highway will be closed as it is too
close to the new intersection and there is sufficient and convenient
access just around the corner.
driveway on Austin Highway closest to Advance Auto Parts will be
closed, also because of its proximity to the new intersection.
existing signals on Austin Highway and on Harry Wurzbach at Eisenhauer
(with the exception of the one discussed in the first point above) will
will be no right turn allowed from the northbound Harry Wurzbach
mainlanes to Eisenhauer Road due to the proximity of the entrance ramp
bike lanes, hike/bike (aka "shared use") paths, crosswalks, and bus
stops are included throughout the project.
to close Thrush View Lane at Eisenhauer and to construct a connector to
Harry Wurzbach instead have been eliminated.
project will help
The new interchange will allow traffic to more easily get
Harry Wurzbach to Austin Highway and vice-versa. The SPUI will allow
the new intersection there to function more efficiently than a
intersection would. The two separate intersections in a
conventional configuration cause left turn movements (for all
approaches) to conflict with each other. As a result, each left turn
movement requires its own protected green for a total of four signal
phases. Because opposing left turns in a SPUI can proceed
simultaneously, this results in only three total signal phases being
required instead of the four in a conventional intersection.
is set to begin in early 2019 and take about two years to complete.
- This looks difficult to navigate.
It will cause lots of crashes.
While it may look complicated on the schematics, it's
actually fairly easy to navigate on the ground. A 1996 study of SPUI
implementations found no significant difference in accident rates or
severity compared to conventional intersections.
- So if this isn't safer than a conventional intersection, why do it?
Because the design means fewer signal phases, which means less
delay for traffic. Since its also no more dangerous than a conventional
intersection, the benefit of the reduced delay easily prevails.
- Are the new left turns flyovers?
the new turning lanes are at the same level as Austin Highway. Harry
Wurzbach will continue to pass under Austin Highway as it does today.
- Will there be turnarounds?
No, there will be no turnarounds at this intersection.
- Why hasn't there been a real intersection here before?
Harry Wurzbach was first built back in the 1940s, its purpose was to
connect Fort Sam Houston to Camp Bullis. Because of that, and because the area around this intersection was
unpopulated, there was little demand to get from Harry Wurzbach to
Austin Highway or vice-versa. Since Austin Highway was the highway to Austin at that time (US 81), it was quite busy, so to avoid conflicts
between military convoys on Harry
Wurzbach and traffic on Austin Highway, the overpass that's there
now was built to separate that traffic.
- Who came up with this cockamamie
The SPUI design has been around for several decades and is in
widespread use in the US and internationally and has a proven
track record of improving traffic wherever it has been implemented. It
is one of several types of "innovative" or "alternative" intersection
designs being implemented across the country at intersections
to improve their efficiency. Since this is a completely new
intersection, the city and TxDOT were able to select the best design
for the location. Since there is no reason for north-south through
traffic at this intersection, a SPUI was a perfect fit.
is the detailed project schematic with annotations as well
as some renderings of the completed project. The
project schematic is courtesy of the City of San Antonio and
change. Annotations are my own. For an animation of the SPUI, see the links at the bottom of this page.
DETAILED PROJECT SCHEMATIC
Click above to see the detailed
annotated schematic for
Looking NE along Austin Highway
Looking SW along Austin Highway
Looking from SE corner
Looking along northbound exit from Harry Wurzbach
Close-up of SPUI intersection
Looking northbound along Harry Wurzbach
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