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Other San Antonio Area Roads
Superstreets

This page last updated March 7, 2021

A "superstreet"-- also known as a "restricted crossing U-turn" or RCUT-- is a roadway where intersections have been modified to eliminate left turns and straight-through traffic on streets that cross a major roadway. Doing this reduces the number of traffic signal phases required to move traffic through the intersection thereby allowing for longer green times on the primary roadway, thus reducing congestion. This is one of several "innovative" or "alternative" intersection types used to improve intersection throughput when grade-separation (overpasses or flyovers) is not possible, not warranted, or too expensive.

The San Antonio area has had three sections of superstreets: one on US 281 North (four intersections), one on Loop 1604 West (two intersections), and one on Bandera Road (currently one intersection.) In the 281 and 1604 cases, the superstreet was in a transition area between the freeway and non-freeway sections of those roads, and both were intended to be short-term improvements while planning was completed and funding acquired to upgrade those segments to freeways. The 281 and 1604 superstreets were the first two superstreets in Texas.

A superstreet intersection was completed on Bandera Rd. at FM 1560 South in 2018. This was the first of several superstreet intersections planned for Bandera Rd. from Loop 1604 to Triana Parkway. Unlike those on US 281 and on Loop 1604, the superstreet plan on Bandera is considered to be a long-term solution for existing and expected congestion.


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Please note that the intersection diagrams below are generalized for the types of intersections involved and not intended to reflect specific existing or future conditions on either 281 or 1604.  They are intended instead to illustrate the concepts being discussed.  Thanks to "SPUI" for the base superstreet illustration used in the intersection diagrams.

On this page:


Local superstreet history

US 281
In February 2009, with the proposed US 281 tollway stalled due to ongoing litigation that resulted in a new environmental study being required, engineers with Pape-Dawson Engineering made an unsolicited proposal to the Alamo Regional Mobility Authority (ARMA) to convert US 281 into a "superstreet" from Encino Rio to Marshall as a short-term fix while the new environmental study for the long-term project on 281 was completed. The plan was expected to increase traffic throughput on 281 by at least 30%, increase average rush hour speeds by about 10 mph in both directions, and reduce travel time by about eight minutes between Loop 1604 and Marshall Rd. The MPO approved funding for this project on March 23rd, 2009. Funding came from a combination of funds from the federal stimulus, Advanced Transportation District, and City of San Antonio. On January 14th, 2010, ARMA's board selected Ballenger Construction's bid of $5.2 million to build the project, which was nearly 20% below the final estimates and nearly 50% below initial projections. Ground was broken on the project on March 11th, 2010. The first intersection (Encino Rio) was completed on August 29th, 2010. Weather delayed work on the Marshall Rd. intersection; it was finally completed on September 26th. The remaining intersections were completed on the weekends of October 2nd and 9th. Construction is now underway to upgrade that section of US 281 to a freeway and three of the four superstreet intersections have now been removed and replaced with conventional access road intersections; the remaining intersection will be converted by mid 2021.

Loop 1604
In October 2009, with plans for the US 281 superstreet nearing completion, the Bexar County Commissioners Court approved funding to study a possible superstreet in the Loop 1604 West corridor, specifically between Braun Rd. and SH 151, as a possible interim solution to ease congestion while ARMA completed an environmental study for long-term improvements there. The superstreet study, completed in early 2010, showed that a combination of conventional and superstreet improvements along that section of 1604 would provide substantial improvements. In May 2010, ARMA previewed the initial designs and expected benefits. Under the plan, the intersections of New Guilbeau and Shaenfield would be reconstructed as superstreet intersections. It was estimated that by doing so, travel speeds could be increased by 36% and delays reduced by 69% during the morning peak and that average travel speeds could be increased by 65% and delays reduced by 79% during the evening peak period. At Braun, the improvements consisted of adding additional through lanes. The superstreet improvements at New Guilbeau and at Shaenfield began construction in March 2011. The New Guilbeau intersection was completed August 18th, followed on September 15th by the Shaenfield intersection. The superstreet intersections were subsequently removed when the corridor was upgraded to a freeway in 2016.

Bandera Road
TxDOT has proposed two superstreet segments along Bandera Rd. One is through Helotes from Loop 1604 to Triana Parkway. Construction on the first intersection-- at FM 1560 South-- was completed in October 2018.
This intersection was the first to be done because a project was already in the works to reconfigure the obsolete and congested dogleg intersection at Circle A Trail, so the superstreet design was incorporated into that project so that the new intersection wouldn't have to be torn-out and redone when the rest of the superstreet corridor is built in the future.

The next two intersections-- at Leslie/Hausman and at Cedar Trail-- are funded and work is expected to start in 2022. The remaining intersections from FM 1560 to Triana are currently unfunded and therefore there is currently no timeline for their completion.

The second proposed segment for Bandera Rd. was between Eckhert and Loop 1604, but after further study was determined to be inadequate as a long-term solution and therefore there are currently no plans for it. Leon Valley has not endorsed a superstreet south of Eckhert. Instead, other proposals are currently being studied.


Conventional intersection operation

Before explaining how a superstreet works, it's important to understand how conventional intersections function, especially with regards to the traffic signal operation. Understanding the signal phasing is vital to grasping the improvements provided by a superstreet. 


What is a signal phase?

A signal "phase" is the green time assigned to a specified movement or collection of movements in a traffic signal cycle. In other words, when the signal is green for a specific movement (straight through, left turn, etc.), that's a signal phase. When it changes to red and another movement gets a green signal, that's another phase. The complete rotation through of all of the phases is a cycle.
 

This is how a typical conventional intersection is configured:

 

The "split-phase" signal configuration typically necessitated by traffic patterns at these intersections requires five signal phases (i.e. signal changes) per cycle (three for the "T" intersections) to allow for each movement through the intersection:

Phase 1


Phase 2


Phase 3


Phase 4


Phase 5


In other words, if you get stopped just as the light is turning red, you have to wait for three or four other directions to have a green light before you get to go.

In a congested intersection, the number of phases and the required length of each phase due to heavy traffic volumes causes overall signal cycles to be long, thus causing long queues and congestion, especially during peak periods. Additionally, each signal phase adds up to 10 or so seconds of "lost" time due to yellow and all-way red clearance intervals as well as the time it takes for stopped motorists to react to a green and to start moving.

Many times, people will say that the signal timings simply need to be adjusted in order to reduce the congestion. In some cases, signal timings can be further optimized to improve conditions. However, in most cases, signals are already optimized as much as they can be and the laws of physics prevent any further efficiency of the existing intersection. When this happens, the intersection must be physically changed.


How a superstreet works

A superstreet reconfigures intersections like this:

At first glance, this can seem quite complicated, but it actually makes sense once you understand how it works and why.

A superstreet intersection eliminates the ability of traffic on the cross street to continue straight through the intersection or to turn left. Instead, all traffic on the cross street must turn right onto the primary road, then use a downstream turnaround to either go the opposite direction or to return to the cross street to continue on it. Those turnarounds are typically located approximately 1000 feet (about 2/10th of a mile) from the intersection they serve to allow sufficient room for merging and storage.

So how does this help? By eliminating the through-traffic and left-turns from the cross streets, the signal phases required for those movements can also be eliminated (or, more specifically, they're combined with the phase for traffic turning left from the primary road onto the cross street.) It is by eliminating those signal phases that the benefit is derived (keep reading.)

While superstreets in areas with low traffic volumes can operate well with stop/yield intersections, most superstreets (including all those in San Antonio) are signalized; in fact, it actually doubles the number of signals in each direction. Yes, it's seems counterintuitive that adding signals can help improve traffic flow. But it's not the number of signals that causes problems, it's the time required to service each movement at the intersection that causes backups. By eliminating the straight-through and left turn movements on the cross street, the number of signal phases (green time for a movement) is reduced from the previous five phases to just two (or from three to two at "T" intersections):

Phase 1


Phase 2

 

That's it-- just two signal phases! Notice how many movements are accomplished in the second phase. This essentially takes phases 4 and 5 and the left turn movements of phases 1 and 3 of the conventional intersection and combines them all into one, eliminating all the time required for those individual phases. In other words, if you get stopped just as the light is turning red, you only have to wait for one other direction to have a green light before it's your turn as opposed to the three or four other directions you have to wait for in the conventional intersection.

Furthermore, significant additional time savings is realized because every signal phase inherently includes some "wasted" time in the form of all-way red clearance intervals as well as the time it takes for drivers to start moving when they get a green light. All of that can add 5-10 seconds of lost time per phase.

All of these time savings allow the green time for through traffic on the primary road to be increased without having to correspondingly reduce the green time for the cross street or lengthen the total cycle time.

It should be noted at this point that the diagrams above for the superstreet signal phases are simplified to show the corresponding phases on both sides of the major road operating simultaneously, but in practice, the phases are usually staggered to better coordinate traffic through the intersections and to optimize the operation of each signal based on the traffic volumes at that time and location. Conceptually, however, this is how the system works.

Superstreet "secret sauce" explained
If the explanation above is still a bit muddy, here's another way of looking at it. Imagine in the diagrams above that you're on the primary road headed from left to right. You reach the conventional intersection just as the light turns red (phase 3.) You then have to wait through phase 3 for 20 seconds, phase 4 for 30 seconds, and phase 5 also for 30 seconds before you get a green light again on phase 1, for a total wait time of 80 seconds
. With the superstreet, all of the movements that took 80 seconds before can now be accomplished in a single 30 second phase, which means that through traffic on the primary road is now only stopped for 30 seconds per cycle instead of 80 second. The 50 seconds of time that's been freed-up by eliminating two phases can be added to the green time for the primary road. So if through traffic previously was allocated 40 seconds of green time, it can get 90 seconds with the superstreet without any change to the overall two minute cycle time. This an obvious and substantial improvement and is where the benefit of a superstreet is derived. See below for a visualization of these timings. (Note that the timings I provide here are for illustrative purposes only and do not necessarily reflect any actual current or previous phase and cycle times.)
 

Example timings
Illustrative red and green signal phase times and associated movements from the perspective of
through traffic on the primary road moving left to right in the diagrams above.
(Be sure to read the explanation in the paragraph above.)


Conventional intersection




Superstreet intersection



Note that the 30 seconds for the cross street could be increased to further reduce congestion there if necessary and still leave significantly more green time for the main road than in a conventional intersection. For example, the cross street could be allocated 40 seconds of green time, leaving 80 seconds for the primary road, which is still twice as much as it had before. This demonstrates the additional flexibility afforded by this design.

Better synchronization
In addition to reducing signal phases, superstreets allow for much better synchronization of the signals. With conventional intersections, signals along a corridor in both directions are inherently interdependent-- in other words, changes cannot be made to one direction without affecting the other. This dependency makes signal coordination and signal progression (or "synchronization") tricky, especially two-way progression. But with a superstreet, the turning movements on one side of the intersection don't affect the other side at all, so the signals for traffic going in one direction on the primary roadway are completely independent of those for the other direction. In effect, each side of the primary road functions like an independent one-way street. This provides the ability to coordinate the signals much more easily and reliably without regards to the number of signals or their spacing, and the signals can react better to the traffic conditions on their side of the road. Essentially, it provides the optimal environment for signal coordination.


Traffic flow through the intersections
While some of the movements through a superstreet intersection are the same as a conventional intersection, some are quite different a bit unintuitive. Below are diagrams depicting the various routes through a superstreet intersection.

Straight-through traffic on the primary road and traffic turning right onto the cross street works just like a conventional intersection:

 

Traffic turning left from the primary road to the cross street also works just like a conventional intersection:

 

And traffic turning right onto the primary road from the cross street works just like a conventional intersection:

 

However, traffic wanting to turn left from the cross street onto the primary road instead turns right, then uses the downstream turnaround to head the other direction:

 

Similarly, traffic wanting to continue straight on the cross street across the primary road instead has to turn right, use the downstream turnaround, then turn right again to get back onto the cross street:

 

Right on red prohibition
Although not required to make a superstreet function, superstreets in San Antonio typically employ a right-on-red prohibition from the cross street. The reason why is two-fold and has to do with the fact that, at a superstreet intersection, many of the vehicles turning right will then subsequently be making a U-turn. Doing this requires them to cross the through traffic lanes. Since a vehicle that makes a right turn on red will be traveling substantially slower than the through traffic and doesn't have a lot of space to get up to speed before merging over, those drivers can create a significant safety hazard as they cross the through traffic lanes. Even if there isn't a collision, vehicles in the through lanes must slow down when encountering someone cutting across to the turnaround; in heavy traffic conditions, this is often the genesis of congestion.

Also, restricting when vehicles can cross creates a "platoon" of vehicles when the light turns green. When signals are coordinated, they are timed to more efficiently move platoons of vehicles, so vehicles crossing over individually while the light is red often won't get that benefit (i.e. still have to wait for the signal at the turnaround anyway.) Yes, this does inconvenience drivers who just want to turn right, but since it's difficult to provide separate regulations for each movement in this situation, the one that provides the greatest overall benefit is usually employed. 

On US 281, an exception to the no turn on red was made for the far right lane at Stone Oak because there was an added lane on southbound 281 at that location, and the traffic in that lane is typically not headed for the turnaround. An additional exception was made for the far right lane at Evans. On Bandera Rd., exceptions were made for Circle A Trail.


Superstreet concerns and complaints

  • It's too confusing for drivers and will causes more accidents: This is always one of the first knee-jerk assertions made when an unconventional intersection is introduced. With any change-- even more conventional changes such as new signals or lanes-- it naturally takes drivers a little time to adapt. With a superstreet, because all traffic on the intersecting street is forced to turn right, most confusion is quickly overcome instinctively once the driver has turned or as the driver follows other more experienced drivers through the intersection. Additionally, because all traffic is flowing in the same direction and is protected by signals, the likelihood of collisions is substantially reduced, even during the adjustment period. Superstreets inherently improve safety by reducing conflict points (the point where vehicle paths cross) by half. And statistics for superstreets show improved safety. A study for the North Carolina DOT showed that superstreets reduced traffic collisions by 46% and decreased crashes with injuries by 63%. A study of superstreet intersections in Missouri showed a 54% reduction in injury and fatal crashes. Many people predicted mayhem at the Bandera/1604 displaced left-turn intersection, but crashes decreased 44% during the first nine months after it was completed.

  • It won't be easy or safe to cross over to the turnarounds or turn from the turnaround: A question often posed by people unfamiliar with superstreets is how traffic from the cross streets can safely merge onto the primary road, then move across the traffic lanes to the turnaround, then merge back into the other direction. The answer is that there are signals that stop the through traffic on the primary road to allow that cross street traffic out at both the main intersection and also again at the turnarounds. As discussed above, even though the signals at the main intersections remain and extra signals are added at the turnarounds, the number of signal phases for all the signals is reduced substantially, thus allowing significantly more green time for the primary road through traffic and signal synchronization is much easier.
     
  • It requires traveling the wrong way/out of the way: Some folks understandably are bothered that to turn left or go straight on the cross street requires going out of one's way to accomplish. This is true and will always be perceived as an inconvenience by many drivers, but because wait times are shorter and overall congestion in the area is reduced, travel time through the intersection is still usually shorter than it would be at a conventional intersection even with the added time necessary to use the turnaround. Also keep in mind that there are many other examples where traffic wanting to make a left turn is prohibited from doing so due to a median, freeway, or one-way street and must therefore turn right first, then make a downstream U-turn or series of left turns, so this situation is not unprecedented or unique to superstreets.
     
  • Pedestrian crossings: Finally, some people have wondered how pedestrians are able to cross these intersections. Below is a diagram of the typical pedestrian crosswalks and pathways in a superstreet intersection, all controlled by signals. Crossing the primary road here is a bit safer than a conventional intersection because it is actually two much shorter crossings.


How a superstreet differs from a "Michigan Left"

People who have lived in Michigan and other parts of the country may be familiar with an intersection layout known as a "Michigan Left", and some have proffered that a superstreet is the same thing just with a different name. However, while a Michigan Left is similar to a superstreet, there are some significant differences between the two:

  • In a Michigan Left, there are no left turns at all. All left turns from both the primary road and cross street are made using the turnarounds. In a superstreet, traffic can make left turns from the primary road onto the cross street but left turns from the cross street are made using the turnarounds.
  • In a Michigan Left, traffic on the cross street can go straight through. In a superstreet, all traffic on the cross street must turn right onto the primary road. Straight-through traffic on the cross street must use the turnaround to return to the intersection, then make a right turn at the intersection to continue in their original direction.

Below are simplified schematics that show the allowed maneuvers in each type of intersection:

Superstreet traffic flow Michigan Left traffic flow
   

Local superstreet results

To objectively measure whether the US 281 superstreet had the intended results, engineers did before-and-after measurements of travel times, average speeds, and traffic volumes. The study found that after the completion of the superstreet, travel times were notably reduced and average speeds increased even though overall traffic volumes increased in the corridor. The table below summarizes the findings. To ensure an "apples-to-apples" comparison, data was collected for Tuesday-Thursday periods when school was in session and when there were no abnormal incidents in the corridor (e.g. accidents, signal malfunctions, bad weather, etc.)

Metric Before Superstreet After Superstreet
Southbound travel time
(Bulverde to Loop 1604, morning rush hour)
23.3 minutes 19.2 minutes
Southbound average speed
(morning rush hour)
16 mph 19 mph
Northbound travel time
(Loop 1604 to Bulverde, evening rush hour)
19.2 minutes 12.7 minutes
Northbound average speed
(evening rush hour)
19 mph 29 mph
Traffic count (north of Evans) 60,100 vehicles/day 63,552 vehicles/day
Traffic count (south of Evans) 74,000 vehicles/day 81,526 vehicles/day

Anecdotal reports for the first few weeks from motorists in the corridor on Facebook, from media reports, and comments on various websites indicated that most of the time, the superstreet provided some relief. Recurring traffic signal malfunctions for the first month or so after completion of the project did cause some initial problems; those were later attributed to the fact that the signal controllers used for the project were a new model and the issues were resolved with assistance from the traffic signal equipment vendor.

Over on Loop 1604, a before-and-after study showed a reduction in peak period travel time of 35% southbound and 14% northbound. The primary reason for the significant discrepancy between northbound and southbound benefits was likely caused by an increase in traffic (induced or latent demand) drawn by the improved conditions of the superstreet exceeding the capacity of the ancillary improvements made at the Braun intersection. This caused traffic to back up at the Braun intersection and cut into the travel time improvements of the superstreet.


Other sites of interest

Pape-Dawson "Superstreets in Texas" presentation
https://drive.google.com/file/d/16b1w_qy_D8A2U_ZWhkG8jtkPZFqcNXlm/view
Wikipedia - Superstreet
https://en.wikipedia.org/wiki/Superstreet
Federal Highway Administration - Restricted Crossing U-Turn Intersection Informational Guide
https://safety.fhwa.dot.gov/intersection/alter_design/pdf/fhwasa14070_rcut_infoguide.pdf
An Update on Superstreet Implementation and Research
http://www.accessmanagement.info/AM08/AM0807Hummer/AM0807Hummer.pdf
NC Department of Transportation presentation on superstreets
(excellent explanation of all aspects of superstreets)

https://www.partnc.org/DocumentCenter/View/331/NCDOT-Superstreet-Presentation-PDF




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