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Pennybacker Bridge
(a.k.a. the "360" bridge; located in Austin, Texas)

This is a scale model of the Pennybacker (a.k.a. "360") Bridge in Austin, Texas. The real bridge is located on the west side of Austin along highway 360 - the Capital of Texas Highway, and it crosses the Colorado River. It is a road and pedestrian bridge.

Model Specs and Facts:
Start date: 31-January-2010
Date of completion: 13-March-2010
Nearly 14,000 pieces used
35-40 pounds in weight (estimated)
Total bridge length = 384 studs (aprox. 120 7/8 inches = 3.1 m)
Free span length = 347 studs (approx. 109 1/4 inches = 2.8 m)
Height (from bottom of abutments) = 37 3/8 inches = 0.95 m)
Total width = 67 studs (approx. 21 1/16 inches = 0.53 m)
Deck width = 48 studs (approx. 15 inches)
Made of 100% LEGO pieces, and no glue was used
Scale = approx. 1:64*
* (could vary between 1:62 and 1:71 depending on reference taken)

The members of the bridge model are covered entirely in dark red plate.

The design and most of the assembly was done by me. Kurt Baty (my LEGO buddy who co-designed and built the Memorial Hermann Tower model with me) helped me with this project. It was initially Kurt's idea to build the Pennybacker during TexLUG's brainstorming and planning session for the March 2010 public display at SXSW (South by Southwest - an annual, very large multimedia conference in Austin, Texas:

The Real Bridge

The Pennybacker Bridge is commonly called the "360 bridge" by locals. It seems that few Austinites know the true name of the bridge.

The construction of the bridge is parallel arched box-sections made of steel. The concrete road deck is suspended beneath the arches. The deck is supported by longitudinal and lateral steel girders underneath. A series of lateral box girders span across the sections of the arch.

There is a small park and public boat ramp on the south end of the bridge. I visited this site in early February 2010 to take a close look for myself.

The most noticeable thing is the lack of coating on the steel (i.e. it's not painted). The chemistry of the steel is such that it is allowed to corrode but will not lose significant amounts of steel over the lifetime of the bridge. In other words, the amount of steel eaten up by the rust will not lead to serious damage - it's just designed to safely rust and stay that way so that it never needs painting.

This is an important aspect of the brige because of the choice of colors for the model (more on that in the next section).

The real bridge is not symmetric along its length. The road deck has a gentle slope from one end to the other. Also, the arches are truncated on the north end due to higher ground on that end versus the south end.

The model is an idealized representation having a level deck and symmetric arches.

10 page
PDF document (0.2 MB)

inventory of dark red

my sketch vs. model

my sketch vs. photo 1

my sketch vs. photo 2

Planning the Model

The basic idea for our SXSW display was to incorporate Austin landmarks if possible. At the time (late January 2010), my 10 foot long arched truss bridge was still built, and I was planning on widening it and using it at the upcoming show. Kurt convinced me to do the new bridge (the Pennybacker), primarily because he offered to provide all the dark red plate required and basically loan me those parts.

The planning and design phase of this model was significant. In fact, I think I spent more time in this phase than actually putting the parts together.

Kurt located a publically available 3D model of the bridge on Google: HERE. I used this to generate to-scale sketches and design the model.

I started planning in late January. The first challenge was to create a design that used the selection of dark red plates that were currently available on This was difficult because the only large plate sizes (in significant quantities) were 4x12 and 6x12.

Kurt and I discussed using alternative colors. Dark bluish gray was the next choice, and it was readily available in just about any size. But Kurt felt strongly that dark red was THE choice. With appropriate modifications in my design and careful planning regarding required parts, we made it work.

I had to generate a detailed inventory of dark red plates so that Kurt could order the parts. I also had to order parts myself. I have a fairly large inventory of Technic beams and other parts, but I still had to order more.

My sketches are contained in a 10-page PDF file (0.2 MB). Note that the design presented in these sketches were changed slightly as I assembled the parts. I had to substitute different parts in a few places, and I also found a few mistakes in my sketches.

demolition of the
previous bridge

My order

350+ 1x14's

3 middle sections
prior to dk. red

end sect. w/ X-braces

test-fit of most arch sect.

assembly at the show

Kurt's order

my order

2000 half-pins

bridge sections

close up of sections

me & the test-fit

assembly at the show

Building the Model & Setting Up

Step one was to disassemble my previous bridge (10 foot long arched truss bridge) because I needed the parts. This was a significant step because there were probably about ten thousand parts in the old bridge.

I started building the arch segments of the Pennybacker first, and at the same time I worked on procuring the other parts I needed. I received Kurt's contribution of dark red plates plus a few other parts. I placed several orders on (including one for 2000 Technic half-pins, and I ended up using all but 20 of those on the bridge).

After assembling nearly all of the arch sections, I fit them together to test the construction. It was flexible but strong. I figured that once I added all the dark red plating that it would be stronger and stiffer, and that would prove to be correct as I found out later.

After the arch sections were complete, I built all the other stuff in just a few hurried building sessions. This included the longitudinal and lateral deck girders, the abutments, and several small items.

The time span between late January and the middle of March had plenty of time for this project. However, life got in the way. To keep it short, we experienced a death in the family, I had medical issues (found out I had a stomach ulcer), sick kids (both of mine- for a few weeks), a nasty 10-day head cold, stomach virus, a home improvement project, etc., etc. It seemed that all the things that could possibly go wrong and prevent me from working on the bridge happened.

I pulled a few late nights and high-speed building sessions in the week before our SXSW showing. I managed to finish building all the major components of the bridge, however I did NOT have time to assemble and test the bridge prior to the show. I also didn't get to place some of the trim and cover pieces on the bridge.

I hauled up all the bridge parts and assembled it on-site for the first time at SXSW. Fortunately, TexLUG had about 10-12 hours total setup time, and that was plenty enough to assemble the bridge. Also, Kurt helped assemble too, and that was a great help.

There were a few very minor issues, but in the end, the bridge went together as I'd planned, and it performed well.

The Show (SXSW)

My photos from the event.
Tony's photos (includes a good series showing the bridge setup).


Many thanks to Kurt for his help with the parts and assembly. Also thanks to some of the TexLUG guys for help handling the assembled arch during the setup. And, many, many thanks to my understanding wife for putting up with my stressed out state and all the build-time that I needed.

Thanks to Tim and Matt who loaned me baseplates and track so that I could complete the bridge deck.

The Future

I plan to keep this bridge assembled for at least a year. We'd like to show it in future TexLUG events, and I also have some plans for improvements.

I came up with a plan to improve the road deck. The design used at SXSW required eight 48x48 X-large baseplates as well as twelve road plates. I think I can build-up a roadway and eliminate the need for the roadplates (so that they can be used in other places on TexLUG's display).

I will also work on the packaging and transportability of the model. For SXSW, I broke down the arch in individual segments (20 pieces in total). I'm planning on shipping the arch in 4 sub-assemblies next time, but I need to make or find an appropriately sized box to contain them.

Thomas J. Avery 2010