Antonio Area Freeway System
INFO: US 281 at Jones-Maltsberger
page last updated December 7, 2018
project is currently in design
descriptions below are based on preliminary schematics and, as
result, details may change before the project goes to construction.
This page will be updated when final schematics for the project are
US 281 at Jones-Maltsberger (South)
planning (see timeline below)
This approximately $5 million project will convert the
intersections at US 281
at Jones-Maltsberger near the Alamo Quarry
Market from conventional intersections to a
Diamond Interchange" (DDI). The
shift traffic in both
directions on Jones-Maltsberger
to the opposite side of
the roadway just before crossing US 281. Traffic will then travel under
US 281 to the left of opposing traffic. This will allow traffic
turning left to US 281 to then make a free left turn onto
the entrance ramp.
Through traffic on Jones-Maltsberger will
then cross back over to the right side
of the roadway. The two crossover
locations will be controlled by a traffic signal. (See
the diagrams below for a depiction of these changes.)
currently no DDIs in San Antonio, but one is proposed at Loop 1604 and
Blanco and another at SE
Military Dr and I-37.
Elsewhere in Texas, there are currently DDIs in El Paso, The Colony,
Round Rock next to the
IKEA. The design
has been used successfully in nearly 100 other locations
the US as well.
companion project at Basse Road
will help to remove traffic from this interchange.
FLOW FOR JONES-MALTSBERGER RD.
the left turns conflict with the opposing through traffic
DIVERGING DIAMOND INTERSECTION (PROPOSED)
TRAFFIC FLOW FOR JONES-MALTSBERGER RD.
Note how the left turns no longer
conflict with the opposing through traffic
CONVENTIONAL INTERSECTION (EXISTING)
FLOW FOR EXIT RAMP LEFT TURNS TO JONES-MALTSBERGER RD.
the left turns conflict
DIVERGING DIAMOND INTERSECTION (PROPOSED)
FLOW FOR EXIT RAMP LEFT
TURNS TO JONES-MALTSBERGER RD.
the left turns no longer conflict
project will help
The DDI will help reduce current
and expected future congestion at this intersection. Current and
projected traffic volumes are sufficient to cause level of service "F"
(congested) conditions during peak periods but are not
sufficient to justify flyovers now or during the next 20 years. Thus,
this intersection is considered to be in the "sweet spot" for an
"outside-the-box" (no pun intended) intersection design. Computer
modeling shows a dramatic improvement in this intersection's operation
a DDI over conventional improvements; the following table
summarizes those findings.
Delay (in seconds) on Jones-Maltsberger
How a DDI
improves traffic flow:
A DDI is a relatively low-cost improvement that increases the
throughput of an intersection by eliminating the conflicts caused by
left turns. This is accomplished by shifting all traffic to the left
side of the road through
the interchange. Doing so then allows two movements that would normally
conflicting to go at the same time. For example, traffic turning left
from the southbound exit ramp can move at the same time as northbound
traffic on Jones-Maltsberger. This overlapping eliminates one of the
two signal phases
required for them in a conventional intersection, making the signals
much more efficient by allowing more traffic to move through the
intersection in the same amount of time.
also improve safety by reducing the number of potential crash points
from 26 to 14 with the worst type (side-angle collisions)
reduced from 10 to just two. Additionally, a DDI physically prevents
turning the wrong way onto the access roads, thus helping to prevent
markings, and signals: To
properly control traffic and minimize potential
signals will be located at the crossover locations as well as the left
turns from the exit ramps. These are simple, two-phase signals
and will be
coordinated and operated from the same signal controller.
lane markings and signage (including large overhead signs) will help
traffic into the correct lanes. The crossover intersections will be
angled sufficiently to make the crossover transition much more
intuitive (engineers have learned from previous projects the optimal
angles for this.)
through a DDI is actually far easier than it may seem from the
diagrams and descriptions.
study of the DDI built in Round Rock in 2016 showed that despite a 50%
increase in afternoon peak period traffic volumes after the DDI was
travel times improved 44-58% over the previous conventional
has also improved
at DDI intersections. A study of safety improvements at DDI
intersections in Colorado showed a 36% reduction in crashes. A 60%
reduction was reported at a DDI in
Springfield, Missouri, where 97% of drivers reported they felt
the DDI was safer
than the previous conventional intersections.
main negative of this intersection is that straight-through traffic
from the exit ramp to the entrance ramp will not be possible. However,
as there are not continuous
frontage roads on either side of this interchange, this should not be
an issue here.
with anything new and unconventional, there will be some skepticism
and initial confusion while drivers learn the new traffic patterns and
adapt. And there are always some naysayers who will perpetually
anything different, innovative, or outside their comfort zone or
is not yet scheduled. As of this writing, it is anticipated that work
could begin in 2021 and take about a year to complete.
- This looks confusing.
It will cause lots of crashes.
While it may look complicated on the schematics, it's
actually fairly easy to navigate on the ground. See the
"how-to" video at the bottom of this page. Statistics from DDI
implementations show a significant reduction in crashes and
practical experience from other DDI locations shows drivers quickly
adapt to it.
- How does this improve
This intersection design improves traffic because shifting the traffic
to the left side of the road through the intersections removes the
conflicts between left turns and opposing traffic found in a
conventional intersection. As a
result, traffic in two of the four legs of the intersection can move
during a single green phase instead of needing two separate
phases, thus moving more traffic through the intersection in the same
amount of time.
- Will there be
No, this project will not add turnarounds. There is insufficient demand
at this location for turnarounds.
- Why not just add the extra
and through lanes?
While this would help move more vehicles through the intersection on
each cycle, the improvements would be short-lived as traffic increases
to fill the new lanes. The
DDI dramatically improves the underlying efficiency of the traffic
signals themselves which provides longer-term relief. See the chart
above that compares projected delay with a DDI versus conventional
- Why not build flyovers instead
like the ones at Bandera and Loop 410?
This intersection does not have current or projected traffic volumes or
- Why don't they build a railroad
a railroad grade separation is very expensive and requires approval
from and extensive cooperation with the railroad. In this location
especially, the proximity of the freeway makes such a project very
challenging. That said, TxDOT and the City of San Antonio are working
with Union Pacific on a long-term plan to construct grade separations
for the railroad at Jones-Maltsberger, Basse, and Sunset. Such a
project is likely a decade or more out, however.
- How is this different than the
intersection under construction at Bandera and Loop 1604?
The DDI is similar to the Displaced Left Turn (DLT) intersection being
built at Bandera and 1604 in
that they are both considered to be types
of "innovative" or "alternative" intersection
that make signalized intersections function better by removing the
inefficiencies caused by protected left turns. Both intersection
designs do this by moving the left turns over to the other side of the
road and out of the way of oncoming traffic. However, in the DLT, it is
just the left turns that are shifted to the other side of the road
whereas the DDI moves both left-turning and through traffic over. A DLT
has its crossovers further away from the main intersection and requires
more signals and right-of-way than a DDI. Also, the DLT does not block
through-traffic on the access road like a DDI does.
Finally, a DLT does not eliminate the conflicting left turns from the
access roads to the cross street like a DDI does.
- Who came up with this cockamamie
The DDI design has been used in France since the 1970s and made its
debut in the United States in 2009. It is now in use in
nearly 100 locations in the US and internationally and has a proven
track record of improving traffic and safety wherever it has been
is one of several types of "innovative" or "alternative" intersection
designs being implemented across the country at intersections
not warrant more expensive conventional upgrades (e.g.
flyovers.) TxDOT selected this design for this intersection
after studying multiple other options. Computer modeling showed this
design provided significant improvement in operations with substantial
reduction in delays. The DDI concept was hailed by Popular Science
one of the top 100 innovations in 2009 and has been featured on
National Public Radio and in Time,
many other publications.
the image below to open the detailed schematic for this
project from TxDOT with my own annotations added to help clarify and
explain the various elements. The schematic will
open in a new window that you can scroll and zoom. Below
a "how-to" video on navigating a DDI.
DETAILED PROJECT SCHEMATIC
video of how to drive through a DDI, see
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