The Texas
Highway Man

Home Search Miscellany Updates About me Contact Menu
San Antonio Area Freeway System
PROJECT INFO: US 281 at Jones-Maltsberger Rd.

This page last updated February 21, 2024

Engineer

This project is currently in design


The descriptions below are based on preliminary schematics and, as a result, details may change before the project goes to construction. This page will be updated when final schematics for the project are available.


Location
  • US 281 at Jones-Maltsberger Rd. (South)

Status
  • Advanced planning

Timeline
  • Construction is not yet scheduled. As of this writing, it is listed to possibly start in 2032 and would take about a year to complete..


ADVERTISEMENT




On this page:


Project description

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 "Diverging Diamond Interchange" (DDI). The DDI will 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.) There are currently no DDIs in San Antonio, but one is under construction at Loop 1604 and Blanco, and another is proposed at SE Military Dr and I‑37. Elsewhere in Texas, there are currently DDIs in El Paso, The Colony, and in Round Rock next to the IKEA. The design has been used successfully in nearly 100 other locations around the US as well

A companion project is planned at the Basse Rd. interchange.

CONVENTIONAL INTERSECTION (EXISTING)
TRAFFIC FLOW FOR JONES-MALTSBERGER RD.

Traffic flow schematic

Note how the left turns conflict with the opposing through traffic

DIVERGING DIAMOND INTERSECTION (PROPOSED)
TRAFFIC FLOW FOR JONES-MALTSBERGER RD.

Traffic flow schematic

Note how the left turns no longer conflict with the opposing through traffic


CONVENTIONAL INTERSECTION (EXISTING)
TRAFFIC FLOW FOR EXIT RAMP LEFT TURNS TO JONES-MALTSBERGER RD.

Traffic flow schematic

Note how the left turns conflict

DIVERGING DIAMOND INTERSECTION (PROPOSED)
TRAFFIC FLOW FOR EXIT RAMP LEFT TURNS TO JONES-MALTSBERGER RD.

Traffic flow schematic

Note how the left turns no longer conflict

(Underlying schematics from TxDOT; annotations added by Brian Purcell)


How this 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 with a DDI over conventional improvements; the following table summarizes those findings.

Delay time chart

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 be 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.

DDIs 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 drivers from turning the wrong way onto the access roads, thus helping to prevent head-on collisions.

DDI

For a deeper dive on how a DDI functions and how it improves traffic flow, see the Blanco Rd./Loop 1604 DDI project page.


FAQ


Schematic

Click on the image below to open the detailed preliminary schematics 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.

Schematic thumbnail

Click the image above for a full-sized schematic of this project


Video

TxDOT has a good video that describes this project:





Other sites of interest

TxDOT - Open House - US 281 at Basse Road and Jones Maltsberger Road Interchanges
https://www.txdot.gov/inside-txdot/get-involved/about/hearings-meetings/san-antonio/101818.html